Froment MT

General

Full name : Froment Marie-Therese

First name : Marie-Therese

Mail : CRSSA, Biochemistry Unit DP 87 - 38702 La Tronche Cedex

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City :

Country : France

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Phone : 33-76-63-59-59

Fax : 33-76-63-69-61

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References (45)

Title : Polyclonal antibody to soman-tyrosine - Li_2013_Chem.Res.Toxicol_26_584
Author(s) : Li B , Duysen EG , Froment MT , Masson P , Nachon F , Jiang W , Schopfer LM , Thiele GM , Klassen LW , Cashman JR , Williams GR , Lockridge O
Ref : Chemical Research in Toxicology , 26 :584 , 2013
Abstract : Soman forms a stable, covalent bond with tyrosine 411 of human albumin, with tyrosines 257 and 593 in human transferrin, and with tyrosine in many other proteins. The pinacolyl group of soman is retained, suggesting that pinacolyl methylphosphonate bound to tyrosine could generate specific antibodies. Tyrosine in the pentapeptide RYGRK was covalently modified with soman simply by adding soman to the peptide. The phosphonylated-peptide was linked to keyhole limpet hemocyanin, and the conjugate was injected into rabbits. The polyclonal antiserum recognized soman-labeled human albumin, soman-mouse albumin, and soman human transferrin but not nonphosphonylated control proteins. The soman-labeled tyrosines in these proteins are surrounded by different amino acid sequences, suggesting that the polyclonal recognizes soman-tyrosine independent of the amino acid sequence. Antiserum obtained after 4 antigen injections over a period of 18 weeks was tested in a competition ELISA where it had an IC50 of 10(-11) M. The limit of detection on Western blots was 0.01 mug (15 picomoles) of soman-labeled albumin. In conclusion, a high-affinity, polyclonal antibody that specifically recognizes soman adducts on tyrosine in a variety of proteins has been produced. Such an antibody could be useful for identifying secondary targets of soman toxicity.
ESTHER : Li_2013_Chem.Res.Toxicol_26_584
PubMedSearch : Li_2013_Chem.Res.Toxicol_26_584
PubMedID: 23469927

Title : Organophosphate hydrolases as catalytic bioscavengers of organophosphorus nerve agents - Trovaslet-Leroy_2011_Toxicol.Lett_206_14
Author(s) : Trovaslet-Leroy M , Musilova L , Renault F , Brazzolotto X , Misik J , Novotny L , Froment MT , Gillon E , Loiodice M , Verdier L , Masson P , Rochu D , Jun D , Nachon F
Ref : Toxicol Lett , 206 :14 , 2011
Abstract : Bioscavengers are molecules able to neutralize neurotoxic organophosphorus compounds (OP) before they can reach their biological target. Human butyrylcholinesterase (hBChE) is a natural bioscavenger each molecule of enzyme neutralizing one molecule of OP. The amount of natural enzyme is insufficient to achieve good protection. Thus, different strategies have been envisioned. The most straightforward consists in injecting a large dose of highly purified natural hBChE to increase the amount of bioscavenger in the bloodstream. This proved to be successful for protection against lethal doses of soman and VX but remains expensive. An improved strategy is to regenerate prophylactic cholinesterases (ChE) by administration of reactivators after exposure. But broad-spectrum efficient reactivators are still lacking, especially for inhibited hBChE. Cholinesterase mutants capable of reactivating spontaneously are another option. The G117H hBChE mutant has been a prototype. We present here the Y124H/Y72D mutant of human acetylcholinesterase; its spontaneous reactivation rate after V-agent inhibition is increased up to 110 fold. Catalytic bioscavengers, enzymes capable of hydrolyzing OP, present the best alternative. Mesophilic bacterial phosphotriesterase (PTE) is a candidate with good catalytic efficiency. Its enantioselectivity has been enhanced against the most potent OP isomers by rational design. We show that PEGylation of this enzyme improves its mean residence time in the rat blood stream 24-fold and its bioavailability 120-fold. Immunogenic issues remain to be solved. Human paraoxonase 1 (hPON1) is another promising candidate. However, its main drawback is that its phosphotriesterase activity is highly dependent on its environment. Recent progress has been made using a mammalian chimera of PON1, but we provide here additional data showing that this chimera is biochemically different from hPON1. Besides, the chimera is expected to suffer from immunogenic issues. Thus, we stress that interest for hPON1 must not fade away, and in particular, the 3D structure of the hPON1 eventually in complex with OP has to be solved.
ESTHER : Trovaslet-Leroy_2011_Toxicol.Lett_206_14
PubMedSearch : Trovaslet-Leroy_2011_Toxicol.Lett_206_14
PubMedID: 21683774

Title : Reaction of cresyl saligenin phosphate, the organophosphorus agent implicated in aerotoxic syndrome, with human cholinesterases: mechanistic studies employing kinetics, mass spectrometry, and X-ray structure analysis - Carletti_2011_Chem.Res.Toxicol_24_797
Author(s) : Carletti E , Schopfer LM , Colletier JP , Froment MT , Nachon F , Weik M , Lockridge O , Masson P
Ref : Chemical Research in Toxicology , 24 :797 , 2011
Abstract : Aerotoxic syndrome is assumed to be caused by exposure to tricresyl phosphate (TCP), an antiwear additive in jet engine lubricants and hydraulic fluid. CBDP (2-(ortho-cresyl)-4H-1,2,3-benzodioxaphosphoran-2-one) is the toxic metabolite of triortho-cresylphosphate, a component of TCP. Human butyrylcholinesterase (BChE; EC 3.1.1.8) and human acetylcholinesterase (AChE; EC 3.1.1.7) are irreversibly inhibited by CBDP. The bimolecular rate constants of inhibition (k(i)), determined under pseudo-first-order conditions, displayed a biphasic time course of inhibition with k(i) of 1.6 x 10(8) M(-1) min(-1) and 2.7 x 10(7) M(-1) min(-1) for E and E' forms of BChE. The inhibition constants for AChE were 1 to 2 orders of magnitude slower than those for BChE. CBDP-phosphorylated cholinesterases are nonreactivatable due to ultra fast aging. Mass spectrometry analysis showed an initial BChE adduct with an added mass of 170 Da from cresylphosphate, followed by dealkylation to a structure with an added mass of 80 Da. Mass spectrometry in (18)O-water showed that (18)O was incorporated only during the final aging step to form phospho-serine as the final aged BChE adduct. The crystal structure of CBDP-inhibited BChE confirmed that the phosphate adduct is the ultimate aging product. CBDP is the first organophosphorus agent that leads to a fully dealkylated phospho-serine BChE adduct.
ESTHER : Carletti_2011_Chem.Res.Toxicol_24_797
PubMedSearch : Carletti_2011_Chem.Res.Toxicol_24_797
PubMedID: 21438623
Gene_locus related to this paper: human-BCHE

Title : Application of laccase-mediator system (LMS) for the degradation of organophosphorus compounds - Trovaslet-Leroy_2010_Chem.Biol.Interact_187_393
Author(s) : Trovaslet-Leroy M , Jolivalt C , Froment MT , Brasme B , Lefebvre B , Daveloose D , Nachon F , Masson P
Ref : Chemico-Biological Interactions , 187 :393 , 2010
Abstract : Degradation of organophosphorus compounds was achieved in the presence of purified fungal laccase from Trametes versicolor and a small molecular weight redox mediator (ABTS). This laccase-mediator system (LMS) catalyzed degradation of VX, PhX and VR while had no apparent effect on CVX, ecothiophate or demeton. Inhibition of ABTS oxidation was shown with VX, PhX, VR and CVX. Results with CVX suggest either no degradation subsequent to interaction with the laccase active site or the formation of a new toxic compound. PhX degradation was also monitored by mass spectroscopy, a method that allowed us to identify certain intermediates formed during OP degradation. Altogether, results underline the importance of the OP nitrogen atom at beta-position and of its substituents, even though the intimate mechanism of laccase-catalyzed degradation is not yet known.
ESTHER : Trovaslet-Leroy_2010_Chem.Biol.Interact_187_393
PubMedSearch : Trovaslet-Leroy_2010_Chem.Biol.Interact_187_393
PubMedID: 20149786

Title : Crystallographic snapshots of nonaged and aged conjugates of soman with acetylcholinesterase, and of a ternary complex of the aged conjugate with pralidoxime - Sanson_2009_J.Med.Chem_52_7593
Author(s) : Sanson B , Nachon F , Colletier JP , Froment MT , Toker L , Greenblatt HM , Sussman JL , Ashani Y , Masson P , Silman I , Weik M
Ref : Journal of Medicinal Chemistry , 52 :7593 , 2009
Abstract : Organophosphate compounds (OP) are potent inhibitors of acetylcholinesterases (AChEs) and can cause lethal poisoning in humans. Inhibition of AChEs by the OP soman involves phosphonylation of the catalytic serine, and subsequent dealkylation produces a form known as the "aged" enzyme. The nonaged form can be reactivated to a certain extent by nucleophiles, such as pralidoxime (2-PAM), whereas aged forms of OP-inhibited AChEs are totally resistant to reactivation. Here, we solved the X-ray crystal structures of AChE from Torpedo californica (TcAChE) conjugated with soman before and after aging. The absolute configuration of the soman stereoisomer adduct in the nonaged conjugate is P(S)C(R). A structural reorientation of the catalytic His440 side chain was observed during the aging process. Furthermore, the crystal structure of the ternary complex of the aged conjugate with 2-PAM revealed that the orientation of the oxime function does not permit nucleophilic attack on the phosphorus atom, thus providing a plausible explanation for its failure to reactivate the aged soman/AChE conjugate. Together, these three crystal structures provide an experimental basis for the design of new reactivators.
ESTHER : Sanson_2009_J.Med.Chem_52_7593
PubMedSearch : Sanson_2009_J.Med.Chem_52_7593
PubMedID: 19642642
Gene_locus related to this paper: torca-ACHE

Title : Direct correlation between molecular dynamics and enzymatic stability: a comparative neutron scattering study of native human butyrylcholinesterase and its aged soman conjugate - Gabel_2009_Biophys.J_96_1489
Author(s) : Gabel F , Masson P , Froment MT , Doctor BP , Saxena A , Silman I , Zaccai G , Weik M
Ref : Biophysical Journal , 96 :1489 , 2009
Abstract : An incoherent elastic neutron scattering study of the molecular dynamics of native human butyrylcholinesterase and its "aged" soman-inhibited conjugate revealed a significant change in molecular flexibility on an angstrom-nanosecond scale as a function of temperature. The results were related to the stability of each state as established previously by differential scanning calorimetry. A striking relationship was found between the denaturation behavior and the molecular flexibility of the native and inhibited enzymes as a function of temperature. This was reflected in a quantitative correlation between the atomic mean-square displacements on an angstrom-nanosecond scale determined by neutron spectroscopy and the calorimetric specific heat. By the application of a simple two-state model that describes the transition from a folded to a denatured state, the denaturation temperatures of the native and the inhibited enzyme were correctly extracted from the atomic mean-square displacements. Furthermore, the transition entropy and enthalpy extracted from the model fit of the neutron data were, within the experimental accuracy, compatible with the values determined by differential scanning calorimetry.
ESTHER : Gabel_2009_Biophys.J_96_1489
PubMedSearch : Gabel_2009_Biophys.J_96_1489
PubMedID: 19217865

Title : Binding and hydrolysis of soman by human serum albumin - Li_2008_Chem.Res.Toxicol_21_421
Author(s) : Li B , Nachon F , Froment MT , Verdier L , Debouzy JC , Brasme B , Gillon E , Schopfer LM , Lockridge O , Masson P
Ref : Chemical Research in Toxicology , 21 :421 , 2008
Abstract : Human plasma and fatty acid free human albumin were incubated with soman at pH 8.0 and 25 degrees C. Four methods were used to monitor the reaction of albumin with soman: progressive inhibition of the aryl acylamidase activity of albumin, the release of fluoride ion from soman, 31P NMR, and mass spectrometry. Inhibition (phosphonylation) was slow with a bimolecular rate constant of 15 +/- 3 M(-1) min (-1). MALDI-TOF and tandem mass spectrometry of the soman-albumin adduct showed that albumin was phosphonylated on tyrosine 411. No secondary dealkylation of the adduct (aging) occurred. Covalent docking simulations and 31P NMR experiments showed that albumin has no enantiomeric preference for the four stereoisomers of soman. Spontaneous reactivation at pH 8.0 and 25 degrees C, measured as regaining of aryl acylamidase activity and decrease of covalent adduct (pinacolyl methylphosphonylated albumin) by NMR, occurred at a rate of 0.0044 h (-1), indicating that the adduct is quite stable ( t1/2 = 6.5 days). At pH 7.4 and 22 degrees C, the covalent soman-albumin adduct, measured by MALDI-TOF mass spectrometry, was more stable ( t1/2 = 20 days). Though the concentration of albumin in plasma is very high (about 0.6 mM), its reactivity with soman (phosphonylation and phosphotriesterase activity) is too slow to play a major role in detoxification of the highly toxic organophosphorus compound soman. Increasing the bimolecular rate constant of albumin for organophosphates is a protein engineering challenge that could lead to a new class of bioscavengers to be used against poisoning by nerve agents. Soman-albumin adducts detected by mass spectrometry could be useful for the diagnosis of soman exposure.
ESTHER : Li_2008_Chem.Res.Toxicol_21_421
PubMedSearch : Li_2008_Chem.Res.Toxicol_21_421
PubMedID: 18163544

Title : An unexpected plasma cholinesterase activity rebound after challenge with a high dose of the nerve agent VX - Dorandeu_2008_Toxicology_248_151
Author(s) : Dorandeu F , Foquin A , Briot R , Delacour C , Denis J , Alonso A , Froment MT , Renault F , Lallement G , Masson P
Ref : Toxicology , 248 :151 , 2008
Abstract : Organophosphorus chemical warfare agents (nerve agents) are to be feared in military operations as well as in terrorist attacks. Among them, VX (O-ethyl-S-[2-(diisopropylamino)ethyl] methylphosphonothioate) is a low volatility liquid that represents a percutaneous as well as an inhalation hazard if aerosolized. It is a potent irreversible cholinesterase (ChE) inhibitor that causes severe signs and symptoms, including respiratory dysfunction that stems from different mechanisms. VX-induced pulmonary oedema was previously reported in dogs but mechanisms involved are not well understood, and its clinical significance remains to be assessed. An experimental model was thus developed to study VX-induced cardiovascular changes and pulmonary oedema in isoflurane-anaesthetized swine. In the course of this study, we observed a fast and unexpected rebound of plasma ChE activity following inhibition provoked by the intravenous injection of 6 and 12 microg kg(-1) of VX. In whole blood ChE activity, the rebound could stay unnoticed. Further investigations showed that the rebound of plasma esterase activity was neither related to spontaneous reactivation of ChE nor to VX-induced increase in paraoxonase/carboxylesterase activities. A bias in Ellman assay, haemoconcentration or severe liver cytolysis were also ruled out. All in all, these results suggest that the rebound was likely due to the release of butyrylcholinesterase into the blood stream from ChE producing organs. Nature of the organ(s) and mechanisms involved in enzyme release will need further investigations as it may represent a mechanism of defence, i.e. VX scavenging, that could advantageously be exploited.
ESTHER : Dorandeu_2008_Toxicology_248_151
PubMedSearch : Dorandeu_2008_Toxicology_248_151
PubMedID: 18450356

Title : Hysteresis of insect acetylcholinesterase - Badiou_2008_Chem.Biol.Interact_175_410
Author(s) : Badiou A , Froment MT , Fournier D , Masson P , Belzunces LP
Ref : Chemico-Biological Interactions , 175 :410 , 2008
Abstract : Pre-steady-state catalytic properties of insect acetylcholinesterase (AChE, EC 3.1.1.7) were studied with the neutral substrate N-methylindoxylacetate. Kinetics of soluble Apis mellifera and Drosophila melanogaster AChE forms showed lags (v(i)=0) before reaching the steady-state. Results were interpreted in terms of slow equilibrium between two conformational states E and E' of insect AChE. Hysteresis of insect AChE has been pointed out for the first time. The hysteretic behaviour was found to depend on the NMIA concentration and the nature of the enzyme. The maximum induction times (tau(max)) to reach the steady-state were 800 and 1000s with soluble AChE from A. mellifera and D.melanogaster, respectively. The orders of magnitude of the tau(max) were high and similar to human AChE and BuChE.
ESTHER : Badiou_2008_Chem.Biol.Interact_175_410
PubMedSearch : Badiou_2008_Chem.Biol.Interact_175_410
PubMedID: 18602377

Title : Kinetic analysis of effector modulation of butyrylcholinesterase-catalysed hydrolysis of acetanilides and homologous esters - Masson_2008_FEBS.J_275_2617
Author(s) : Masson P , Froment MT , Gillon E , Nachon F , Lockridge O , Schopfer LM
Ref : Febs J , 275 :2617 , 2008
Abstract : The effects of tyramine, serotonin and benzalkonium on the esterase and aryl acylamidase activities of wild-type human butyrylcholinesterase and its peripheral anionic site mutant, D70G, were investigated. The kinetic study was carried out under steady-state conditions with neutral and positively charged aryl acylamides [o-nitrophenylacetanilide, o-nitrotrifluorophenylacetanilide and m-(acetamido) N,N,N-trimethylanilinium] and homologous esters (o-nitrophenyl acetate and acetylthiocholine). Tyramine was an activator of hydrolysis for neutral substrates and an inhibitor of hydrolysis for positively charged substrates. The affinity of D70G for tyramine was lower than that of the wild-type enzyme. Tyramine activation of hydrolysis for neutral substrates by D70G was linear. Tyramine was found to be a pure competitive inhibitor of hydrolysis for positively charged substrates with both wild-type butyrylcholinesterase and D70G. Serotonin inhibited both esterase and aryl acylamidase activities for both positively charged and neutral substrates. Inhibition of wild-type butyrylcholinesterase was hyperbolic (i.e. partial) with neutral substrates and linear with positively charged substrates. Inhibition of D70G was linear with all substrates. A comparison of the effects of tyramine and serotonin on D70G versus the wild-type enzyme indicated that: (a) the peripheral anionic site is involved in the nonlinear activation and inhibition of the wild-type enzyme; and (b) in the presence of charged substrates, the ligand does not bind to the peripheral anionic site, so that ligand effects are linear, reflecting their sole interaction with the active site binding locus. Benzalkonium acted as an activator at low concentrations with neutral substrates. High concentrations of benzalkonium caused parabolic inhibition of the activity with neutral substrates for both wild-type butyrylcholinesterase and D70G, suggesting multiple binding sites. Benzalkonium caused linear, noncompetitive inhibition of the positively charged aryl acetanilide m-(acetamido) N,N,N-trimethylanilinium for D70G, and an unusual mixed-type inhibition/activation (alpha > beta > 1) for wild-type butyrylcholinesterase with this substrate. No fundamental difference was observed between the effects of ligands on the butyrylcholinesterase-catalysed hydrolysis of esters and amides. Thus, butyrylcholinesterase uses the same machinery, i.e. the catalytic triad S198/H448/E325, for the hydrolysis of both types of substrate. The differences in response to ligand binding depend on whether the substrates are neutral or positively charged, i.e. the differences depend on the function of the peripheral site in wild-type butyrylcholinesterase, or the absence of its function in the D70G mutant. The complex inhibition/activation effects of effectors, depending on the integrity of the peripheral anionic site, reflect the allosteric 'cross-talk' between the peripheral anionic site and the catalytic centre.
ESTHER : Masson_2008_FEBS.J_275_2617
PubMedSearch : Masson_2008_FEBS.J_275_2617
PubMedID: 18422653

Title : Aging of cholinesterases phosphylated by tabun proceeds through O-dealkylation - Carletti_2008_J.Am.Chem.Soc_130_16011
Author(s) : Carletti E , Li H , Li B , Ekstrom F , Nicolet Y , Loiodice M , Gillon E , Froment MT , Lockridge O , Schopfer LM , Masson P , Nachon F
Ref : Journal of the American Chemical Society , 130 :16011 , 2008
Abstract : Human butyrylcholinesterase (hBChE) hydrolyzes or scavenges a wide range of toxic esters, including heroin, cocaine, carbamate pesticides, organophosphorus pesticides, and nerve agents. Organophosphates (OPs) exert their acute toxicity through inhibition of acetylcholinesterase (AChE) by phosphorylation of the catalytic serine. Phosphylated cholinesterase (ChE) can undergo a spontaneous, time-dependent process called "aging", during which the OP-ChE conjugate is dealkylated. This leads to irreversible inhibition of the enzyme. The inhibition of ChEs by tabun and the subsequent aging reaction are of particular interest, because tabun-ChE conjugates display an extraordinary resistance toward most current oxime reactivators. We investigated the structural basis of oxime resistance for phosphoramidated ChE conjugates by determining the crystal structures of the non-aged and aged forms of hBChE inhibited by tabun, and by updating the refinement of non-aged and aged tabun-inhibited mouse AChE (mAChE). Structures for non-aged and aged tabun-hBChE were refined to 2.3 and 2.1 A, respectively. The refined structures of aged ChE conjugates clearly show that the aging reaction proceeds through O-dealkylation of the P(R) enantiomer of tabun. After dealkylation, the negatively charged oxygen forms a strong salt bridge with protonated His438N epsilon2 that prevents reactivation. Mass spectrometric analysis of the aged tabun-inhibited hBChE showed that both the dimethylamine and ethoxy side chains were missing from the phosphorus. Loss of the ethoxy is consistent with the crystallography results. Loss of the dimethylamine is consistent with acid-catalyzed deamidation during the preparation of the aged adduct for mass spectrometry. The reported 3D data will help in the design of new oximes capable of reactivating tabun-ChE conjugates.
ESTHER : Carletti_2008_J.Am.Chem.Soc_130_16011
PubMedSearch : Carletti_2008_J.Am.Chem.Soc_130_16011
PubMedID: 18975951
Gene_locus related to this paper: human-BCHE , mouse-ACHE

Title : Aryl acylamidase activity of human serum albumin with o-nitrotrifluoroacetanilide as the substrate - Masson_2007_J.Enzyme.Inhib.Med.Chem_22_463
Author(s) : Masson P , Froment MT , Darvesh S , Schopfer LM , Lockridge O
Ref : J Enzyme Inhib Med Chem , 22 :463 , 2007
Abstract : Albumin is generally regarded as an inert protein with no enzyme activity. However, albumin has esterase activity as well as aryl acylamidase activity. A new acetanilide substrate, o-nitrotrifluoroacetanilide (o-NTFNAC), which is more reactive than the classical o-nitroacetanilide, made it possible to determine the catalytic parameters for hydrolysis by fatty-acid free human serum albumin. Owing to the low enzymatic activity of albumin, kinetic studies were performed at high albumin concentration (0.075 mM). The albumin behavior with this substrate was Michaelis-Menten like. Kinetic analysis was performed according to the formalism used for catalysis at high enzyme concentration. This approach provided values for the turnover and dissociation constant of the albumin-substrate complex: k(cat) = 0.13 +/- 0.02 min(-1) and Ks = 0.67 +/- 0.04 mM. MALDI-TOF experiments showed that unlike the ester substrate p-nitrophenyl acetate, o-NTFNAC does not form a stable adduct (acetylated enzyme). Kinetic analysis and MALDI-TOF experiments demonstrated that hydrolysis of o-NTFNAC by albumin is fully rate-limited by the acylation step (k(cat) = k2). Though the aryl acylamidase activity of albumin is low (k(cat)/Ks = 195 M(-1)min(-1)), because of its high concentration in human plasma (0.6-1 mM), albumin may participate in hydrolysis of aryl acylamides through second-order kinetics. This suggests that albumin may have a role in the metabolism of endogenous and exogenous aromatic amides, including drugs and xenobiotics.
ESTHER : Masson_2007_J.Enzyme.Inhib.Med.Chem_22_463
PubMedSearch : Masson_2007_J.Enzyme.Inhib.Med.Chem_22_463
PubMedID: 17847714

Title : Kinetic analysis of butyrylcholinesterase-catalyzed hydrolysis of acetanilides - Masson_2007_Biochim.Biophys.Acta_1774_1139
Author(s) : Masson P , Froment MT , Gillon E , Nachon F , Darvesh S , Schopfer LM
Ref : Biochimica & Biophysica Acta , 1774 :1139 , 2007
Abstract : The aryl-acylamidase (AAA) activity of butyrylcholinesterase (BuChE) has been known for a long time. However, the kinetic mechanism of aryl-acylamide hydrolysis by BuChE has not been investigated. Therefore, the catalytic properties of human BuChE and its peripheral site mutant (D70G) toward neutral and charged aryl-acylamides were determined. Three neutral (o-nitroacetanilide, m-nitroacetanilide, o-nitrophenyltrifluoroacetamide) and one positively charged (3-(acetamido) N,N,N-trimethylanilinium, ATMA) acetanilides were studied. Hydrolysis of ATMA by wild-type and D70G enzymes showed a long transient phase preceding the steady state. The induction phase was characterized by a hysteretic "burst". This reflects the existence of two enzyme states in slow equilibrium with different catalytic properties. Steady-state parameters for hydrolysis of the three acetanilides were compared to catalytic parameters for hydrolysis of esters giving the same acetyl intermediate. Wild-type BuChE showed substrate activation while D70G displayed a Michaelian behavior with ATMA as with positively charged esters. Owing to the low affinity of BuChE for amide substrates, the hydrolysis kinetics of neutral amides was first order. Acylation was the rate-determining step for hydrolysis of aryl-acetylamide substrates. Slow acylation of the enzyme, relative to that by esters may, in part, be due suboptimal fit of the aryl-acylamides in the active center of BuChE. The hypothesis that AAA and esterase active sites of BuChE are non-identical was tested with mutant BuChE. It was found that mutations on the catalytic serine, S198C and S198D, led to complete loss of both activities. The silent variant (FS117) had neither esterase nor AAA activity. Mutation in the peripheral site (D70G) had the same effect on esterase and AAA activities. Echothiophate inhibited both activities identically. It was concluded that the active sites for esterase and AAA activities are identical, i.e. S198. This excludes any other residue present in the gorge for being the catalytic nucleophile pole.
ESTHER : Masson_2007_Biochim.Biophys.Acta_1774_1139
PubMedSearch : Masson_2007_Biochim.Biophys.Acta_1774_1139
PubMedID: 17690023

Title : Hydrolysis of oxo- and thio-esters by human butyrylcholinesterase - Masson_2007_Biochim.Biophys.Acta_1774_16
Author(s) : Masson P , Froment MT , Gillon E , Nachon F , Lockridge O , Schopfer LM
Ref : Biochimica & Biophysica Acta , 1774 :16 , 2007
Abstract : Catalytic parameters of human butyrylcholinesterase (BuChE) for hydrolysis of homologous pairs of oxo-esters and thio-esters were compared. Substrates were positively charged (benzoylcholine versus benzoylthiocholine) and neutral (phenylacetate versus phenylthioacetate). In addition to wild-type BuChE, enzymes containing mutations were used. Single mutants at positions: G117, a key residue in the oxyanion hole, and D70, the main component of the peripheral anionic site were tested. Double mutants containing G117H and mutations on residues of the oxyanion hole (G115, A199), or the pi-cation binding site (W82), or residue E197 that is involved in stabilization of tetrahedral intermediates were also studied. A mathematical analysis was used to compare data for BuChE-catalyzed hydrolysis of various pairs of oxo-esters and thio-esters and to determine the rate-limiting step of catalysis for each substrate. The interest and limitation of this method is discussed. Molecular docking was used to analyze how the mutations could have altered the binding of the oxo-ester or the thio-ester. Results indicate that substitution of the ethereal oxygen for sulfur in substrates may alter the adjustment of substrate in the active site and stabilization of the transition-state for acylation. This affects the k2/k3 ratio and, in turn, controls the rate-limiting step of the hydrolytic reaction. Stabilization of the transition state is modulated both by the alcohol and acyl moieties of substrate. Interaction of these groups with the ethereal hetero-atom can have a neutral, an additive or an antagonistic effect on transition state stabilization, depending on their molecular structure, size and enantiomeric configuration.
ESTHER : Masson_2007_Biochim.Biophys.Acta_1774_16
PubMedSearch : Masson_2007_Biochim.Biophys.Acta_1774_16
PubMedID: 17182295

Title : Aging pathways for organophosphate-inhibited human butyrylcholinesterase, including novel pathways for isomalathion, resolved by mass spectrometry - Li_2007_Toxicol.Sci_100_136
Author(s) : Li H , Schopfer LM , Nachon F , Froment MT , Masson P , Lockridge O
Ref : Toxicol Sci , 100 :136 , 2007
Abstract : Some organophosphorus compounds are toxic because they inhibit acetylcholinesterase (AChE) by phosphylation of the active site serine, forming a stable conjugate: Ser-O-P(O)-(Y)-(XR) (where X can be O, N, or S and Y can be methyl, OR, or SR). The inhibited enzyme can undergo an aging process, during which the X-R moiety is dealkylated by breaking either the P-X or the X-R bond depending on the specific compound, leading to a nonreactivatable enzyme. Aging mechanisms have been studied primarily using AChE. However, some recent studies have indicated that organophosphate-inhibited butyrylcholinesterase (BChE) may age through an alternative pathway. Our work utilized matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry to study the aging mechanism of human BChE inhibited by dichlorvos, echothiophate, diisopropylfluorophosphate (DFP), isomalathion, soman, sarin, cyclohexyl sarin, VX, and VR. Inhibited BChE was aged in the presence of H2O18 to allow incorporation of (18)O, if cleavage was at the P-X bond. Tryptic-peptide organophosphate conjugates were identified through peptide mass mapping. Our results showed no aging of VX- and VR-treated BChE at 25 degrees C, pH 7.0. However, BChE inhibited by dichlorvos, echothiophate, DFP, soman, sarin, and cyclohexyl sarin aged exclusively through O-C bond cleavage, i.e., the classical X-R scission pathway. In contrast, isomalathion aged through both X-R and P-X pathways; the main aged product resulted from P-S bond cleavage and a minor product resulted from O-C and/or S-C bond cleavage.
ESTHER : Li_2007_Toxicol.Sci_100_136
PubMedSearch : Li_2007_Toxicol.Sci_100_136
PubMedID: 17698511

Title : Rat butyrylcholinesterase-catalysed hydrolysis of N-alkyl homologues of benzoylcholine - Hrabovska_2006_FEBS.J_273_1185
Author(s) : Hrabovska A , Debouzy JC , Froment MT , Devinsky F , Paulikova I , Masson P
Ref : Febs J , 273 :1185 , 2006
Abstract : The purpose of this work was to study the catalytic properties of rat butyrylcholinesterase with benzoylcholine (BzCh) and N-alkyl derivatives of BzCh (BCHn) as substrates. Complex hysteretic behaviour was observed in the approach to steady-state kinetics for each ester. Hysteresis consisted of a long lag phase with damped oscillation. The presence of a long lag phase, with no oscillations, in substrate hydrolysis by rat butyrylcholinesterase was also observed with N-methylindoxyl acetate as substrate. Hysteretic behaviour was explained by the existence of two interconvertible butyrylcholinesterase forms in slow equilibrium, while just one of them is catalytically active. The damped oscillations were explained by the existence of different substrate conformational states and/or aggregates (micelles) in slow equilibrium. Different substrate conformational states were confirmed by 1H-NMR. The K(m) values for substrates decreased as the length of the alkyl chain increased. High affinity of the enzyme for the longest alkyl chain length substrates was explained by multiple hydrophobic interactions of the alkyl chain with amino acid residues lining the active site gorge. Molecular modelling studies supported this interpretation; docking energy decreased as the length of the alkyl chain increased. The long-chain substrates had reduced k(cat) values. Docking studies showed that long-chain substrates were not optimally oriented in the active site for catalysis, thus explaining the slow rate of hydrolysis. The hydrolytic rate of BCH12 and longer alkyl chain esters vs. substrate concentration showed a premature plateau far below V(max). This was due to the loss of substrate availability. The best substrates for rat butyrylcholinesterase were short alkyl homologues, BzCh - BCH4.
ESTHER : Hrabovska_2006_FEBS.J_273_1185
PubMedSearch : Hrabovska_2006_FEBS.J_273_1185
PubMedID: 16519684

Title : Mutant of Bungarus fasciatus acetylcholinesterase with low affinity and low hydrolase activity toward organophosphorus esters - Poyot_2006_Biochim.Biophys.Acta_1764_1470
Author(s) : Poyot T , Nachon F , Froment MT , Loiodice M , Wieseler S , Schopfer LM , Lockridge O , Masson P
Ref : Biochimica & Biophysica Acta , 1764 :1470 , 2006
Abstract : Enzymes hydrolysing highly toxic organophosphate esters (OPs) are promising alternatives to pharmacological countermeasures against OPs poisoning. Bungarus fasciatus acetylcholinesterase (BfAChE) was engineered to acquire organophosphate hydrolase (OPase) activity by reproducing the features of the human butyrylcholinesterase G117H mutant, the first mutant designed to hydrolyse OPs. The modification consisted of a triple mutation on the (122)GFYS(125) peptide segment, resulting in (122)HFQT(125). This substitution introduced a nucleophilic histidine above the oxyanion hole, and made space in that region. The mutant did not show inhibition by excess acetylthiocholine up to 80 mM. The k(cat)/K(m) ratio with acetylthiocholine was 4 orders of magnitude lower than that of wild-type AChE. Interestingly, due to low affinity, the G122H/Y124Q/S125T mutant was resistant to sub-millimolar concentrations of OPs. Moreover, it had hydrolysing activity with paraoxon, echothiophate, and diisopropyl phosphofluoridate (DFP). DFP was characterised as a slow-binding substrate. This mutant is the first mutant of AChE capable of hydrolysing organophosphates. However, the overall OPase efficiency was greatly decreased compared to G117H butyrylcholinesterase.
ESTHER : Poyot_2006_Biochim.Biophys.Acta_1764_1470
PubMedSearch : Poyot_2006_Biochim.Biophys.Acta_1764_1470
PubMedID: 16962835

Title : Synthesis of 2-substituted beta-cyclodextrin derivatives with a hydrolytic activity against the organophosphorylester paraoxon - Masurier_2005_Eur.J.Med.Chem_40_615
Author(s) : Masurier N , Estour F , Froment MT , Lefevre B , Debouzy JC , Brasme B , Masson P , Lafont O
Ref : Eur Journal of Medicinal Chemistry , 40 :615 , 2005
Abstract : Beta-cyclodextrin was substituted by an iodosobenzoic acid derivative to create a catalytic hydrolytic activity against neurotoxic organophosphorus agents. The catalytic moiety was introduced on a secondary hydroxy group at the position 2 of a glucose unit. Several beta-cyclodextrin derivatives were obtained. In these derivatives, the methylene linker occupied all potential positions on the aromatic ring. Kinetic assays were carried out with paraoxon as organophosphate model. Three regioisomers hydrolyzed paraoxon, although the paraoxon-leaving group, para-nitrophenol, was not released from the beta-cyclodextrin torus.
ESTHER : Masurier_2005_Eur.J.Med.Chem_40_615
PubMedSearch : Masurier_2005_Eur.J.Med.Chem_40_615
PubMedID: 15935896

Title : Hysteresis of butyrylcholinesterase in the approach to steady-state kinetics - Masson_2005_Chem.Biol.Interact_157-158_143
Author(s) : Masson P , Schopfer LM , Froment MT , Debouzy JC , Nachon F , Gillon E , Lockridge O , Hrabovska A , Goldstein BN
Ref : Chemico-Biological Interactions , 157-158 :143 , 2005
Abstract : Butyrylcholinesterase (BChE) displays hysteretic behavior with certain neutral and charged substrates in the approach to steady state. Previous studies led us to interpret this phenomenon in terms of slow transitions between two enzyme conformers E and E'. This kinetic peculiarity is observed in human, horse and rat BChE. Oscillations that superimpose on the hysteretic lag are observed when benzoylcholine and N-alkyl derivatives of benzoylcholine are used as substrate. Hysteresis of BChE can be modulated by medium parameters (pH, salts, temperature, and pressure). Though mutant enzymes show different hysteretic behavior, so far attempts to provide a molecular mechanism of BChE hysteresis from mutagenesis studies have been unproductive. However, the substrate dependence of the hysteretic induction times, using wild-type BChE and several mutants, allowed us to build a general, mechanistic model for the hysteresis. In this model, substrate can bind to E, E', or both conformers, and ES and/or E'S can be catalytically active. The exact pathway followed depends on both the nature of the substrate and the structure of the BChE mutant under study. We propose that oscillations develop when substrate exists in different, slowly interconvertible, conformational and/or aggregation forms, of which only the minor form is capable of reacting with BChE. In support of this proposal, NMR studies have provided direct evidence for slow equilibria between monomeric and micellar forms of long-chain, alkyl derivatives of benzoyl-(N-substituted) choline. There is no direct evidence that hysteresis plays a role in BChE function(s). However, the "new view" of protein dynamics proposes that proteins are normally in equilibrium between pre-existing, functional and non-functional conformers; and that binding a ligand to the functional form shifts that equilibrium towards the functional conformation. Therefore, a physiological or toxicological relevance for the hysteresis in BChE cannot be ruled out.
ESTHER : Masson_2005_Chem.Biol.Interact_157-158_143
PubMedSearch : Masson_2005_Chem.Biol.Interact_157-158_143
PubMedID: 16256969

Title : Contribution of the active-site metal cation to the catalytic activity and to the conformational stability of phosphotriesterase: temperature- and pH-dependence - Rochu_2004_Biochem.J_380_627
Author(s) : Rochu D , Viguie N , Renault F , Crouzier D , Froment MT , Masson P
Ref : Biochemical Journal , 380 :627 , 2004
Abstract : Phosphotriesterase (PTE) detoxifies nerve agents and organophosphate pesticides. The two zinc cations of the PTE active centre can be substituted by other transition metal cations without loss of activity. Furthermore, metal-substituted PTEs display differences in catalytic properties. A prerequisite for engineering highly efficient mutants of PTE is to improve their thermostability. Isoelectric focusing, capillary electrophoresis and steady-state kinetics analysis were used to determine the contribution of the active-site cations Zn2+, Co2+ or Cd2+ to both the catalytic activity and the conformational stability of the corresponding PTE isoforms. The three isoforms have different pI values (7.2, 7.5 and 7.1) and showed non-superimposable electrophoretic titration curves. The overall structural alterations, causing changes in functional properties, were found to be related to the nature of the bound cation: ionic radius and ion electronegativity correlate with Km and kcat respectively. In addition, the pH-dependent activity profiles of isoforms were different. The temperature-dependent profiles of activity showed maximum activity at T < or =35 degrees C, followed by an activation phase near 45-48 degrees C and then inactivation which was completed at 60 degrees C. Analysis of thermal denaturation of the PTEs provided evidence that the activation phase resulted from a transient intermediate. Finally, at the optimum activity between pH 8 and 9.4, the thermostability of the different PTEs increased as the pH decreased, and the metal cation modulated stability (Zn2+-, Co2+- and Cd2+-PTE showed different T (m) values of 60.5-67 degrees C, 58-64 degrees C and 53-64 degrees C respectively). Requirements for optimum activity of PTE (displayed by Co2+-PTE) and maximum stability (displayed by Zn2+-PTE) were demonstrated.
ESTHER : Rochu_2004_Biochem.J_380_627
PubMedSearch : Rochu_2004_Biochem.J_380_627
PubMedID: 15018612

Title : Rate-determining step of butyrylcholinesterase-catalyzed hydrolysis of benzoylcholine and benzoylthiocholine. Volumetric study of wild-type and D70G mutant behavior - Masson_2004_Eur.J.Biochem_271_1980
Author(s) : Masson P , Bec N , Froment MT , Nachon F , Balny C , Lockridge O , Schopfer LM
Ref : European Journal of Biochemistry , 271 :1980 , 2004
Abstract : The rate-limiting step for hydrolysis of the positively charged oxoester benzoylcholine (BzCh) by human butyrylcholinesterase (BCHE) is deacylation (k(3)), whereas it is acylation (k(2)) for hydrolysis of the homologous thioester benzoylthiocholine (BzSCh). Steady-state hydrolysis of BzCh and BzSCh by wild-type BCHE and its peripheral anionic site mutant D70G was investigated at different hydrostatic pressures, which allowed determination of volume changes associated with substrate binding, and the activation volumes for the chemical steps. A differential nonlinear pressure-dependence of the catalytic parameters for hydrolysis of both substrates by both enzymes was shown. Nonlinearity of the plots may be explained in terms of compressibility changes or rate-limiting changes. To distinguish between these two possibilities, enzyme phosphorylation by diisopropylfluorophosphate (DFP) in the presence of substrate (BzSCh) under pressure was studied. There was no pressure dependence of volume changes for DFP binding or for phosphorylation of either wild-type or D70G. Analysis of the pressure dependence for steady-state hydrolysis of substrates, and for phosphorylation by DFP provided evidence that no enzyme compressibility changes occurred during the catalyzed reactions. Thus, the nonlinear pressure dependence of substrate hydrolysis reflects changes in the rate-limiting step with pressure. Change in rate-determining step occurred at a pressure of 100 MPa for hydrolysis of BzCh by wild-type and at 75 MPa for D70G. For hydrolysis of BzSCh the change occurred at higher pressures because k(2) << k(3) at atmospheric pressure for this substrate. Elementary volume change contributions upon initial binding, productive binding, acylation and deacylation were calculated from the pressure differentiation of kinetic constants. This analysis shed light on the molecular events taking place along the hydrolysis pathways of BzCh and BzSCh by wild-type BCHE and the D70G mutant. In addition, volume change differences between wild-type and D70G provided new evidence that residue D70 in the peripheral site controls hydration of the active site gorge and the dynamics of the water molecule network during catalysis. Finally, a steady-state kinetic study of the oxyanion hole mutant (G117H) showed that substitution of the ethereal sulfur for oxygen in the substrate alters the final adjustment of substrate in the active site and stabilization of the acylation transition state.
ESTHER : Masson_2004_Eur.J.Biochem_271_1980
PubMedSearch : Masson_2004_Eur.J.Biochem_271_1980
PubMedID: 15128307

Title : Damped oscillatory hysteretic behaviour of butyrylcholinesterase with benzoylcholine as substrate - Masson_2004_Eur.J.Biochem_271_220
Author(s) : Masson P , Goldstein BN , Debouzy JC , Froment MT , Lockridge O , Schopfer LM
Ref : European Journal of Biochemistry , 271 :220 , 2004
Abstract : Steady-state kinetics for the hydrolysis of benzoylcholine (BzCh) and benzoylthiocholine (BzSCh) by wild-type human butyrylcholinesterase (BuChE) and by the peripheral anionic site mutant D70G were compared. kcat/Km for the hydrolysis of BzSCh was 17-fold and 32-fold lower than that for hydrolysis of BzCh by wild-type and D70G, respectively. The rate-limiting step for hydrolysis of BzCh was deacylation, whereas acylation was rate-limiting for hydrolysis of BzSCh. Wild-type enzyme and the D70G mutant were found to reach steady-state velocity slowly with BzCh as the substrate. At pH 6, the approach to steady-state for both enzymes consisted of a mono-exponential acceleration upon which a set of damped oscillations was superimposed. From pH 7 to 8.5, the approach to steady-state consisted of a simple exponential acceleration. The damped oscillations were analyzed by both a numerical approximation and simulation based on a theoretical model. BuChE-catalyzed hydrolysis of the thiocholine analogue of BzCh showed neither lags nor oscillations, under the same conditions. The frequency and amplitude of the damped oscillations decreased as the BzCh concentration increased. The apparent induction time for the exponential portion of the lag was calculated from the envelope of the damped oscillations or from the smooth lag. Wild-type BuChE showed a hyperbolic increase in induction time as the BzCh concentration increased (tau max = 210 s at pH 6.0). However, the induction time for D70G was constant over the whole range of BzCh concentrations (tau max = 60 s at pH 6.0). Thus, the induction time does not conform to a simple hysteretic model in which there is a slow conformational transition of the enzyme from an inactive form E to an active form E'. No pH-dependence of the induction time was found between pH 6.0 and 8.5 in sodium phosphate buffers of various concentrations (from 1 mm to 1 m). However, increasing the pH tended to abolish the oscillations (increase the damping factor). This effect was more pronounced for D70G than for wild-type. Although the lyotropic properties of phosphate change from chaotropic at pH 6.0 to kosmotropic at pH > 8.0, no effect of phosphate concentration on the oscillations was noticed at the different pH values, suggesting that the oscillations are not related to a pH-dependent Hofmeister effect of phosphate ions. Simulation and theoretical analysis of the oscillatory behaviour of the approach to the steady-state for BuChE led us to propose a model for the hysteresis of BuChE with BzCh. In this model, the substrate-free enzyme is present as an equilibrium mixture of two forms, E and E'. Substrate binds to E and E', but only Epsilon'S makes products. It is proposed that oscillations originate from a time-dependent change in the local concentration, solvation and/or conformation of substrate in the bulk solution. 1H-NMR measurements provided evidence for a slow equilibrium between two BzCh conformers. Binding of the conformationally preferred substrate conformer leads to products.
ESTHER : Masson_2004_Eur.J.Biochem_271_220
PubMedSearch : Masson_2004_Eur.J.Biochem_271_220
PubMedID: 14686935

Title : Hysteresis in butyrylcholinesterase catalysis. -
Author(s) : Masson P , Froment MT , Nachon F , Schopfer LM
Ref : Cholinergic Mechanisms, CRC Press :637 , 2004
PubMedID:

Title : Hysteretic behavior of butyrylcholinesterase: Kinetic curiosity or catalytically and physiologicaly significant? -
Author(s) : Masson P , Froment MT , Nachon F , Lockridge O , Schopfer LM
Ref : In: Cholinesterases in the Second Millennium: Biomolecular and Pathological Aspects , (Inestrosa NC, Campos EO) P. Universidad Catolica de Chile-FONDAP Biomedicina :191 , 2004
PubMedID:

Title : Poster (20) Hysteretic behavior of butyrylcholinesterase : kinetic curiosity or catalytically and physiologically significant? -
Author(s) : Masson P , Froment MT , Nachon F , Lockridge O , Schopfer LM
Ref : In: Cholinesterases in the Second Millennium: Biomolecular and Pathological Aspects , (Inestrosa NC, Campos EO) P. Universidad Catolica de Chile-FONDAP Biomedicina :331 , 2004
PubMedID:

Title : High activity of human butyrylcholinesterase at low pH in the presence of excess butyrylthiocholine - Masson_2003_Eur.J.Biochem_270_315
Author(s) : Masson P , Nachon F , Bartels CF , Froment MT , Ribes F , Matthews C , Lockridge O
Ref : European Journal of Biochemistry , 270 :315 , 2003
Abstract : Butyrylcholinesterase is a serine esterase, closely related to acetylcholinesterase. Both enzymes employ a catalytic triad mechanism for catalysis, similar to that used by serine proteases such as alpha-chymotrypsin. Enzymes of this type are generally considered to be inactive at pH values below 5, because the histidine member of the catalytic triad becomes protonated. We have found that butyrylcholinesterase retains activity at pH
ESTHER : Masson_2003_Eur.J.Biochem_270_315
PubMedSearch : Masson_2003_Eur.J.Biochem_270_315
PubMedID: 12605682

Title : Substrate activation in acetylcholinesterase induced by low pH or mutation in the pi-cation subsite - Masson_2002_Biochim.Biophys.Acta_1594_313
Author(s) : Masson P , Schopfer LM , Bartels CF , Froment MT , Ribes F , Nachon F , Lockridge O
Ref : Biochimica & Biophysica Acta , 1594 :313 , 2002
Abstract : Substrate inhibition is considered a defining property of acetylcholinesterase (AChE), whereas substrate activation is characteristic of butyrylcholinesterase (BuChE). To understand the mechanism of substrate inhibition, the pH dependence of acetylthiocholine hydrolysis by AChE was studied between pH 5 and 8. Wild-type human AChE and its mutants Y337G and Y337W, as well as wild-type Bungarus fasciatus AChE and its mutants Y333G, Y333A and Y333W were studied. The pH profile results were unexpected. Instead of substrate inhibition, wild-type AChE and all mutants showed substrate activation at low pH. At high pH, there was substrate inhibition for wild-type AChE and for the mutant with tryptophan in the pi-cation subsite, but substrate activation for mutants containing small residues, glycine or alanine. This is particularly apparent in the B. fasciatus AChE. Thus a single amino acid substitution in the pi-cation site, from the aromatic tyrosine of B. fasciatus AChE to the alanine of BuChE, caused AChE to behave like BuChE. Excess substrate binds to the peripheral anionic site (PAS) of AChE. The finding that AChE is activated by excess substrate supports the idea that binding of a second substrate molecule to the PAS induces a conformational change that reorganizes the active site.
ESTHER : Masson_2002_Biochim.Biophys.Acta_1594_313
PubMedSearch : Masson_2002_Biochim.Biophys.Acta_1594_313
PubMedID: 11904227

Title : Butyrylcholinesterase-catalyzed hydrolysis of N-methylindoxyl acetate: analysis of volume changes upon reaction and hysteretic behavior - Masson_2002_Biochim.Biophys.Acta_1597_229
Author(s) : Masson P , Froment MT , Fort S , Ribes F , Bec N , Balny C , Schopfer LM
Ref : Biochimica & Biophysica Acta , 1597 :229 , 2002
Abstract : Hydrolysis of the neutral substrate N-methylindoxyl acetate (NMIA) by wild-type human butyrylcholinesterase (BuChE) and peripheral site mutants (D70G, Y332A, D70G/Y332A) was found to follow the Michaelis-Menten kinetics. K(m) was 0.14 mM for wild-type, and 0.07-0.16 mM for D70G, Y332A and D70G/Y332A, indicating that the peripheral site is not involved in NMIA binding. The values of k(cat) were of the same order for all enzymes: 12,000-18,000 min(-1). Volume changes upon substrate binding (-DeltaV(K(m))) and the activation volumes (DeltaV++(k(cat)) associated with hydrolysis of NMIA were calculated from the pressure dependence of the catalytic constants. Values of -DeltaV(K(m)) indicate that NMIA binds to an aromatic residue, presumed to be W82, the active site binding locus. Binding is accompanied by a release of water molecules from the gorge. Residue 70 controls the number of water molecules that are released upon substrate binding. The values of DeltaV++(k(cat)), which are positive for wild-type and faintly positive for D70G, clearly indicate that the catalytic steps are accompanied by re-entry of water into the gorge. Results support the premise that residue D70 is involved in the conformational stabilization of the active site gorge and in control of its hydration. A slow transient, preceding the steady state, was seen on a time scale of several minutes. The induction time rapidly increased with NMIA concentration to reach a limit at substrate saturation. Much shorter induction times (<1 min) were seen for hydrolysis of benzoylcholine (BzCh) by wild-type BuChE and for hydrolysis of butyrylthiocholine (BuSCh) by the active site mutants E197Q and E197Q/G117H. This slow transient was interpreted in terms of hysteresis without kinetic cooperativity. The hysteretic behavior of BuChE results from a slow conformational equilibrium between two enzyme states E and E'. NMIA binds only to the primed form E'. Kosmotropic salts and hydrostatic pressure were found to shift the equilibrium toward E'. The E-->E' transition is accompanied by a negative activation volume (DeltaV++(0)= -45+/-10 ml/mol), and the E' form is more compact than E. Hydration water in the gorge of E' appears to be more structured than in the unprimed form.
ESTHER : Masson_2002_Biochim.Biophys.Acta_1597_229
PubMedSearch : Masson_2002_Biochim.Biophys.Acta_1597_229
PubMedID: 12044901

Title : Concentration-dependent reversible activation-inhibition of human butyrylcholinesterase by tetraethylammonium ion - Stojan_2002_Eur.J.Biochem_269_1154
Author(s) : Stojan J , Golicnik M , Froment MT , Estour F , Masson P
Ref : European Journal of Biochemistry , 269 :1154 , 2002
Abstract : Tetraalkylammonium (TAA) salts are well known reversible inhibitors of cholinesterases. However, at concentrations around 10 mm, they have been found to activate the hydrolysis of positively charged substrates, catalyzed by wild-type human butyrylcholinesterase (EC 3.1.1.8) [Erdoes, E.G., Foldes, F.F., Zsigmond, E.K., Baart, N. & Zwartz, J.A. (1958) Science 128, 92]. The present study was undertaken to determine whether the peripheral anionic site (PAS) of human BCHE (Y332, D70) and/or the catalytic substrate binding site (CS) (W82, A328) are involved in this phenomenon. For this purpose, the kinetics of butyrylthiocholine (BTC) hydrolysis by wild-type human BCHE, by selected mutants and by horse BCHE was carried out at 25 degreeC and pH 7.0 in the presence of tetraethylammonium (TEA). It appears that human enzymes with more intact structure of the PAS show more prominent activation phenomenon. The following explanation has been put forward: TEA competes with the substrate at the peripheral site thus inhibiting the substrate hydrolysis at the CS. As the inhibition by TEA is less effective than the substrate inhibition itself, it mimics activation. At the concentrations around 40 mm, well within the range of TEA competition at both substrate binding sites, it lowers the activity of all tested enzymes.
ESTHER : Stojan_2002_Eur.J.Biochem_269_1154
PubMedSearch : Stojan_2002_Eur.J.Biochem_269_1154
PubMedID: 11856351

Title : Effects of mutations of active site residues and amino acids interacting with the Omega loop on substrate activation of butyrylcholinesterase - Masson_2001_Biochim.Biophys.Acta_1544_166
Author(s) : Masson P , Xie W , Froment MT , Lockridge O
Ref : Biochimica & Biophysica Acta , 1544 :166 , 2001
Abstract : The peripheral anionic site (PAS) of human butyrylcholinesterase is involved in the mechanism of substrate activation by positively charged substrates and ligands. Two substrate binding loci, D70 in the PAS and W82 in the active site, are connected by the Omega loop. To determine whether the Omega loop plays a role in the signal transduction between the PAS and the active site, residues involved in stabilization of the loop, N83, K339 and W430, were mutated. Mutations N83A and N83Q caused loss of substrate activation, suggesting that N83 which interacts with the D70 backbone may be an element of the transducing system. The K339M and W430A mutant enzymes retained substrate activation. Residues W82, E197, and A328 in the active site gorge have been reported to be involved in substrate activation. At butyrylthiocholine concentrations greater then 2 mM, W82A showed apparent substrate activation. Mutations E197Q and E197G strongly reduced substrate activation, while mutation E197D caused a moderate effect, suggesting that the carboxylate of residue E197 is involved in substrate activation. Mutations A328F and A328Y showed no substrate activation, whereas A328G retained substrate activation. Substrate activation can result from an allosteric effect due to binding of the second substrate molecule on the PAS. Mutation W430A was of special interest because this residue hydrogen bonds to W82 and Y332. W430A had strongly reduced affinity for tetramethylammonium. The bimolecular rate constant for reaction with diisopropyl fluorophosphate was reduced 10000-fold, indicating severe alteration in the binding area in W430A. The kcat values for butyrylthiocholine, o-nitrophenyl butyrate, and succinyldithiocholine were lower. This suggested that the mutation had caused misfolding of the active site gorge without altering the Omega loop conformation/dynamics. W430 as well as W231 and W82 appear to form the wall of the active site gorge. Mutation of any of these tryptophans disrupts the architecture of the active site.
ESTHER : Masson_2001_Biochim.Biophys.Acta_1544_166
PubMedSearch : Masson_2001_Biochim.Biophys.Acta_1544_166
PubMedID: 11341926
Gene_locus related to this paper: human-BCHE

Title : Polyol-induced activation by excess substrate of the D70G butyrylcholinesterase mutant - Levitsky_1999_Biochim.Biophys.Acta_1429_422
Author(s) : Levitsky V , Xie W , Froment MT , Lockridge O , Masson P
Ref : Biochimica & Biophysica Acta , 1429 :422 , 1999
Abstract : Wild-type human butyrylcholinesterase (BCHE) has a non-Michaelian behaviour showing substrate activation with butyrylthiocholine (BTC) as the substrate. The D70G mutant has a catalytic constant identical to that of the wild-type enzyme, but a 10-fold lower affinity for BTC compared to wild-type enzyme, and it does not exhibit activation by excess BTC under conventional conditions. In the present work it was found that addition of polyols or sugars changed the kinetic behaviour of the D70G mutant with BTC. In the presence of 40% sucrose, the D70G mutant enzyme displayed marked activation by excess substrate. Because D70 is hydrogen bonded to Y332, mutants of Y332 were studied. Mutant Y332F had a behaviour similar to that of wild-type BCHE, whereas mutants Y332A, Y332A/D70G and D70G had negligible substrate activation. The behavior of wild-type, Y332F, Y332A and Y332A/D70G did not change in the presence of high concentrations of sugar. Substrate activation has been explained by binding of a second substrate molecule in the peripheral site at D70. The D70G mutant should be incapable of substrate activation, if D70 were the only residue involved in substrate activation. The ability of the D70G mutant to display substrate activation by medium engineering suggests that other residues are involved in initial substrate binding and activation by excess substrate. Osmolyte-induced change in conformation and/or hydration status of Y332 and other solvent-exposed residues may account for the non-Michaelian behaviour of the D70G mutant.
ESTHER : Levitsky_1999_Biochim.Biophys.Acta_1429_422
PubMedSearch : Levitsky_1999_Biochim.Biophys.Acta_1429_422
PubMedID: 9989227

Title : Interaction between the peripheral site residues of human butyrylcholinesterase, D70 and Y332, in binding and hydrolysis of substrates - Masson_1999_Biochim.Biophys.Acta_1433_281
Author(s) : Masson P , Xie W , Froment MT , Levitsky V , Fortier PL , Albaret C , Lockridge O
Ref : Biochimica & Biophysica Acta , 1433 :281 , 1999
Abstract : Human butyrylcholinesterase displays substrate activation with positively charged butyrylthiocholine (BTC) as the substrate. Peripheral anionic site (PAS) residues D70 and Y332 appear to be involved in the initial binding of charged substrates and in activation control. To determine the contribution of PAS residues to binding and hydrolysis of quaternary substrates and activation control, the single mutants D70G/Y and Y332F/A/D and the double mutants Y332A/D70G and Y332D/D70Y were studied. Steady-state hydrolysis of the charged substrates, BTC and succinyldithiocholine, and the neutral ester o-nitrophenyl butyrate was measured. In addition, inhibition of wild-type and mutant enzymes by tetramethylammonium was investigated, at low concentrations of BTC. Single and double mutants of D70 and Y332 showed little or no substrate activation, suggesting that both residues were important for activation control. The effects of double mutations on D70 and Y332 were complex. Double-mutant cycle analysis provided evidence for interaction between these residues. The category of interaction (either synergistic, additive, partially additive or antagonistic) was found to depend on the nature of the substrate and on measured binding or kinetic parameters. This complexity reflects both the cross-talk between residues involved in the sequential formation of productive Michaelian complexes and the effect of peripheral site residues on catalysis. It is concluded that double mutations on the PAS induce a conformational change in the active site gorge of butyrylcholinesterase that can alter both substrate binding and enzyme acylation.
ESTHER : Masson_1999_Biochim.Biophys.Acta_1433_281
PubMedSearch : Masson_1999_Biochim.Biophys.Acta_1433_281
PubMedID: 10446378

Title : Stability of the Quaternary Structure of Butyrylcholinesterase Subjected to Ultrasound or Hydrostatic Pressure -
Author(s) : Froment MT , Clery C , Weingand-Ziade A , Masson P
Ref : In: Structure and Function of Cholinesterases and Related Proteins - Proceedings of Sixth International Meeting on Cholinesterases , (Doctor, B.P., Taylor, P., Quinn, D.M., Rotundo, R.L., Gentry, M.K. Eds) Plenum Publishing Corp. :436 , 1998
PubMedID:

Title : Absence of a protective effect of the oxime 2-PAM toward paraoxon-poisoned honey bees: acetylcholinesterase reactivation not at fault - Polyzou_1998_Toxicol.Appl.Pharmacol_152_184
Author(s) : Polyzou A , Froment MT , Masson P , Belzunces LP
Ref : Toxicol Appl Pharmacol , 152 :184 , 1998
Abstract : We investigated the failure of 2-PAM to protect honey bees against poisoning with paraoxon. The protective effect of the oxime 2-PAM against inhibition of acetylcholinesterase (AChE) by paraoxon was estimated in vitro and in vivo and was correlated with the mortality of paraoxon-treated bees. In vitro, 2-PAM protected 90% of AChE activity in the presence of paraoxon and reactivated more than 90% of inhibited AChE. Minor soluble and major membrane-bound forms of bee AChE presented about similar extents of reactivation, but the first order rate constant of reactivation (kobs) of the soluble form is threefold higher than that of the membrane-bound form. However, this difference did not significantly influence the reactivation kinetics of total AChE; the constant kobs of the membrane-bound form reflected that of total AChE. The linear kinetic profile of total AChE reactivation supported the conclusion that there was a single population of reactivatable species. The bimolecular rate constant of reactivation (kr), the dephosphorylation rate constant (k2), and the dissociation constant (Kd) were 646 M-1.min-1, 0.84 min-1 and 1. 30 mM, respectively. In vivo, administration of 2-PAM, after paraoxon exposure, induced a complete protection of AChE activity, but did not elicit any significant effect on mortality in paraoxon-treated bees. The inefficiency of 2-PAM to antagonize paraoxon-induced mortality was not changed by the administration of 2-PAM in pretreatment-therapy and in therapy treatments. These results indicated that the mortality of paraoxon-poisoned honey bees was not due to a lack of AChE reactivation.
ESTHER : Polyzou_1998_Toxicol.Appl.Pharmacol_152_184
PubMedSearch : Polyzou_1998_Toxicol.Appl.Pharmacol_152_184
PubMedID: 9772214

Title : Shielding of Acetylcholinesterase does not Result in the Protection of Honey Bee against Poisoning by Organophosphates -
Author(s) : Polyzou A , Froment MT , Masson P , Belzunces LP
Ref : In: Structure and Function of Cholinesterases and Related Proteins - Proceedings of Sixth International Meeting on Cholinesterases , (Doctor, B.P., Taylor, P., Quinn, D.M., Rotundo, R.L., Gentry, M.K. Eds) Plenum Publishing Corp. :552 , 1998
PubMedID:

Title : Resistance of butyrylcholinesterase to inactivation by ultrasound: effects of ultrasound on catalytic activity and subunit association - Froment_1998_Biochim.Biophys.Acta_1387_53
Author(s) : Froment MT , Lockridge O , Masson P
Ref : Biochimica & Biophysica Acta , 1387 :53 , 1998
Abstract : The effects of 20 kHz ultrasound on catalytic activity and structure of the tetramer of wild-type human butyrylcholinesterase (BChE) from plasma and recombinant D70G mutant enzyme were studied at constant temperature. Effects on catalytic properties of both enzymes were investigated by kinetic analysis under ultrasound irradiation using a neutral substrate (o-nitrophenylbutyrate), a positively charged substrate (butyrylthiocholine), and a negatively charged substrate (aspirin). Effects on structure of highly purified wild-type BChE were followed by gel electrophoresis and activity measurements at Vmax after ultrasound treatment. Unlike hydrostatic pressure, mild ultrasound had moderate effects on catalytic parameters of BChE-catalyzed hydrolysis of substrates. For both wild-type and D70G, Km increased slightly with butyrylthiocholine and o-nitrophenylbutyrate under ultrasound irradiation, suggesting that these effects of ultrasound were not due to the periodic variation of pressure but rather to shear forces that took off substrate from the peripheral site and altered diffusion to the active site. By contrast, affinity of the D70G mutant for aspirin slightly increased with ultrasound power, suggesting that ultrasound-induced microstreaming unmasked peripheral residues involved in recognition and initial binding of the negatively charged substrate. Results support the contention that Km is a composite affinity constant, including dissociation constant of the first encounter enzyme-substrate complex on the peripheral site. Small changes in catalytic activity may have resulted from ultrasound-induced subtle conformational changes altering the active site reactivity. Short ultrasound irradiation induced a faint transient enzyme activation, but prolonged irradiation caused partial dissociation of the tetrameric enzyme and irreversible inactivation. Partial dissociation was related to enzyme microheterogeneity, i.e., nicked (C-terminal segment depleted) tetramers were less stable than native tetramers. The resistance of the native tetramer to ultrasound-induced dissociation was ascribed to the existence of an aromatic amino acid array on the apolar side of the C-terminal helical segment of subunits, the four subunits being held together in a four-helix bundle containing the aromatic zipper motifs. Aromatic/aromatic interactions between the four helical segments are thought to be enhanced by ultrasound-generated pressure.
ESTHER : Froment_1998_Biochim.Biophys.Acta_1387_53
PubMedSearch : Froment_1998_Biochim.Biophys.Acta_1387_53
PubMedID: 9748500

Title : Butyrylcholinesterase-catalysed hydrolysis of aspirin, a negatively charged ester, and aspirin-related neutral esters - Masson_1998_Biochim.Biophys.Acta_1387_41
Author(s) : Masson P , Froment MT , Fortier PL , Visicchio JE , Bartels CF , Lockridge O
Ref : Biochimica & Biophysica Acta , 1387 :41 , 1998
Abstract : Although aspirin (acetylsalicylic acid) is negatively charged, it is hydrolysed by butyrylcholinesterase (BCHE). Catalytic parameters were determined in 100 mM Tris buffer, pH 7.4, in the presence and absence of metal cations. The presence of Ca2+ or Mg2+ (<100 mM) in buffer did not change the Km, but accelerated the rate of hydrolysis of aspirin by wild-type or D70G mutant BCHE by 5-fold. Turnover numbers were of the order of 5000-12000 min-1 for the wild-type enzyme and the D70G and D70K enzymes in 100 mM Tris, pH 7.4, containing 50 mM CaCl2 at 25 degreesC; Km values were 6 mM for wild-type, 16 mM for D70G and 38 mM for D70K. People with 'atypical' BCHE have the D70G mutation. The apparent inhibition seen at high aspirin concentration was not due to inhibition by excess substrate but to spontaneous hydrolysis of aspirin, causing inhibition by salicylate. The wild-type and D70G enzymes were competitively inhibited by salicylic acid; the D70K enzyme showed a complex parabolic inhibition, suggesting multiple binding. The effect of salicylate was substrate-dependent, the D70K mutant being activated by salicylate with butyrylthiocholine as substrate. Km value for wild-type enzyme was lower than for D70 mutants, suggesting that residue 70 located at the rim of the active site gorge was not the major site for the initial encounter aspirin-BCHE complex. On the other hand, the virtual absence of affinity of the W82A mutant for aspirin indicated that W82 was the major residue involved in formation of the Michaelis complex. Molecular modelling of aspirin binding to BCHE indicated perpendicular interactions between the aromatic rings of W82 and aspirin. Kinetic study of BCHE-catalysed hydrolysis of different acetyl esters showed that the rate limiting step was acetylation. The bimolecular rate constants for hydrolysis of aspirin by wild-type, D70G and D70K enzymes were found to be close to 1x106 M-1 min-1. These results support the contention that the electrostatic steering due to the negative electrostatic field of the enzyme plays a role in substrate binding, but plays no role in the catalytic steps, i.e. in the enzyme acetylation.
ESTHER : Masson_1998_Biochim.Biophys.Acta_1387_41
PubMedSearch : Masson_1998_Biochim.Biophys.Acta_1387_41
PubMedID: 9748494

Title : A single amino acid substitution, Gly117His, confers phosphotriesterase (organophosphorus acid anhydride hydrolase) activity on human butyrylcholinesterase - Lockridge_1997_Biochemistry_36_786
Author(s) : Lockridge O , Blong RM , Masson P , Froment MT , Millard CB , Broomfield CA
Ref : Biochemistry , 36 :786 , 1997
Abstract : The G117H mutant of human butyrylcholinesterase (EC 3.1.1.8) was expressed in Chinese hamster ovary cells. Substitution of Gly 117 with His to make the G117H mutant endowed butyrylcholinesterase with the ability to catalyze the hydrolysis of organophosphate esters. G117H was still able to hydrolyze butyrylthiocholine, benzoylcholine, and o-nitrophenyl butyrate, but in addition it had acquired the ability to hydrolyze the antiglaucoma drug echothiophate and the pesticide paraoxon. Wild-type butyrylcholinesterase was irreversibly inhibited by echothiophate and paraoxon, but G117H regained 100% activity within 2-3 min following reaction with these compounds. On a polyacrylamide gel, the same bands that stained for activity with butyrylthiocholine also stained for activity with echothiophate. G117H is the only enzyme known that hydrolyzes echothiophate. Diethoxyphosphorylated G117H aged with a half-time of 5.5 h, a rate 600 times slower than the rate of hydrolysis. Echothiophate and paraoxon were hydrolyzed with the same kcat of 0.75 min-1. This calculates to a rate acceleration of 100,000-fold for hydrolysis of echothiophate and paraoxon by the G117H mutant compared to the nonenzymatic rate.
ESTHER : Lockridge_1997_Biochemistry_36_786
PubMedSearch : Lockridge_1997_Biochemistry_36_786
PubMedID: 9020776

Title : Importance of aspartate-70 in organophosphate inhibition, oxime re-activation and aging of human butyrylcholinesterase - Masson_1997_Biochem.J_325_53
Author(s) : Masson P , Froment MT , Bartels CF , Lockridge O
Ref : Biochemical Journal , 325 :53 , 1997
Abstract : Asp-70 is the defining amino acid in the peripheral anionic site of human butyrylcholinesterase (BCHE), whereas acetylcholinesterase has several additional amino acids, the most important one being Trp-277 (Trp-279 in Torpedo AChE). We studied mutants D70G, D70K and A277W to evaluate the role of Asp-70 and Trp-277 in reactions with organophosphates. We found that Asp-70 was important for binding positively charged echothiophate, but not neutral paraoxon and iso-OMPA. Asp-70 was also important for binding of positively charged pralidoxime (2-PAM) and for activation of re-activation by excess 2-PAM. Excess 2-PAM had an effect similar to substrate activation, suggesting the binding of 2 mol of 2-PAM to wild-type but not to the D70G mutant. A surprising result was that Asp-70 was important for irreversible aging, the D70G mutant having a 3- and 8-fold lower rate of aging for paraoxon-inhibited and di-isopropyl fluorophosphate-inhibited BCHE. Mutants of Asp-70 had the same rate constants for phosphorylation and re-activation by 2-PAM as wild-type. The A277W mutant behaved like wild-type in all assays. Our results predict that people with the atypical (D70G) variant of BCHE will be more sensitive to the toxic effects of echothiophate, but will be equally sensitive to paraoxon and di-isopropyl fluorophosphate. People with the D70G mutation will be resistant to re-activation of their inhibited BCHE by 2-PAM, but this will be offset by the lower rate of irreversible aging of inhibited BCHE, allowing some regeneration by spontaneous hydrolysis.
ESTHER : Masson_1997_Biochem.J_325_53
PubMedSearch : Masson_1997_Biochem.J_325_53
PubMedID: 9224629

Title : Role of aspartate 70 and tryptophan 82 in binding of succinyldithiocholine to human butyrylcholinesterase - Masson_1997_Biochemistry_36_2266
Author(s) : Masson P , Legrand P , Bartels CF , Froment MT , Schopfer LM , Lockridge O
Ref : Biochemistry , 36 :2266 , 1997
Abstract : The atypical variant of human butyrylcholinesterase has Gly in place of Asp 70. Patients with this D70G mutation respond abnormally to the muscle relaxant succinyldicholine, experiencing hours of apnea rather than the intended 3 min. Asp 70 is at the rim of the active site gorge 12 A from the active site Ser 198. An unanswered question in the literature is why the atypical variant has a 10-fold increase in Km for compounds with a single positive charge but a 100-fold increase in Km for compounds with two positive charges. We mutated residues Asp 70, Trp 82, Trp 231, Glu 197, and Tyr 332 and expressed mutant enzymes in mammalian cells. Steady-state kinetic parameters for hydrolysis of butyrylthiocholine, benzoylcholine, succinyldithiocholine, and o-nitrophenyl butyrate were determined. The wild type and the D70G mutant had identical k(cat) values for all substrates. Molecular modeling and molecular dynamics suggested that succinyldicholine could bind in two consecutive orientations in the active site gorge; formation of one complex caused a conformational change in the omega loop involving Asp 70 and Trp 82. We propose the formation of three enzyme-substrate intermediates preceding the acyl-enzyme intermediate; kinetic data support this contention. Substrates with a single positive charge interact with Asp 70 just once, whereas substrates with two positive charges, for example succinyldithiocholine, interact with Asp 70 in two complexes, thus explaining the 10- and 100-fold increases in Km in the D70G mutant.
ESTHER : Masson_1997_Biochemistry_36_2266
PubMedSearch : Masson_1997_Biochemistry_36_2266
PubMedID: 9047329

Title : Aging of di-isopropyl-phosphorylated human butyrylcholinesterase - Masson_1997_Biochem.J_327_601
Author(s) : Masson P , Fortier PL , Albaret C , Froment MT , Bartels CF , Lockridge O
Ref : Biochemical Journal , 327 ( Pt 2) :601 , 1997
Abstract : Organophosphate-inhibited cholinesterases can be reactivated by nucleophilic compounds. Sometimes phosphylated (phosphorylated or phosphonylated) cholinesterases become progressively refractory to reactivation; this can result from different reactions. The most frequent process, termed 'aging', involves the dealkylation of an alkoxy group on the phosphyl moiety through a carbocation mechanism. In attempting to determine the amino acid residues involved in the aging of butyrylcholinesterase (BuChE), the human BuChE gene was mutated at several positions corresponding to residues located at the rim of the active site gorge and in the vicinity of the active site. Mutant enzymes were expressed in Chinese hamster ovary cells. Wild-type BuChE and mutants were inhibited by di-isopropylfluorophosphate at pH 8.0 and 25 degrees C. Di-isopropyl-phosphorylated enzymes were incubated with the nucleophilic oxime 2-pyridine aldoxime methiodide and their reactivatability was determined. Reactivatability was expressed by the first-order rate constant of aging and/or the half-life of aging (t12). The t12 was found to be of the order of 60 min for wild-type BuChE. Mutations on Glu-197 increased t12 60-fold. Mutation W82A increased t12 13-fold. Mutation D70G increased t12 8-fold. Mutations in the vicinity of the active site serine residue had either moderate or no effect on aging; t12 was doubled for F329C and F329A, increased only 4-fold for the double mutant A328G+F329S, and no change was observed for the A328G mutant, indicating that the isopropoxy chain to be dealkylated does not directly interact with Ala-328 and Phe-329. These results were interpreted by molecular modelling of di-isopropylphosphorylated wild-type and mutant enzymes. Molecular dynamics simulations indicated that the isopropyl chain that is lost interacted with Trp-82, suggesting that Trp-82 has a role in stabilizing the carbonium ion that is released in the dealkylation step. This study emphasized the important role of the Glu-197 carboxylate in stabilizing the developing carbocation, and the allosteric control of the dealkylation reaction by Asp-70. Indeed, although Asp-70 does not interact with the phosphoryl moiety, mutation D70G affects the rate of aging. This indirect control was interpreted in terms of change in the conformational state of Trp-82 owing to internal motions of the Omega loop (Cys-65-Cys-92) in the mutant enzyme.
ESTHER : Masson_1997_Biochem.J_327_601
PubMedSearch : Masson_1997_Biochem.J_327_601
PubMedID: 9359435

Title : Asp7O in the peripheral anionic site of human butyrylcholinesterase - Masson_1996_Eur.J.Biochem_235_36
Author(s) : Masson P , Froment MT , Bartels CF , Lockridge O
Ref : European Journal of Biochemistry , 235 :36 , 1996
Abstract : The goal of this work was to determine what amino acids at the mouth of the active-site gorge are important for the function of human butyrylcholinesterase. Mutants D70G, Q119Y, G283D, A277W, A277H and A277W/G283D were expressed in human embryonal kidney cells and the secreted enzymes were assayed by steady-state kinetics. The result was that only one amino acid, D70 was found to be important for function. When D70 was mutated to G, the same mutation as in the naturally occurring atypical butyrylcholinesterase, the affinity for positively charged substrates and positively charged inhibitors decreased 5-30-fold. The D70G mutant had another striking abnormality in that it was virtually devoid of the phenomenon of substrate activation by excess butyrylthiocholine. Thus, though kcat was the same for wild-type and D70G mutant, being 24000 min(-1) at low butyrylthiocholine concentrations (0.01-0.1 mM), it failed to increase for the D70G mutant at 40 mM butyrylthiocholine, whereas it increased threefold for wild type. The D70G mutant was more sensitive to changes in salt concentration, its catalytic rate decreasing more than that of the wild type. The D70G mutant appeared to have a greater surface negative charge than wild type suggesting that the D70G mutant had a conformation different from that of the wild type. That D70 affects the function of butyrylcholinesterase, together with its location at the mouth of the active-site gorge, supports the hypothesis that D70 is a component of the peripheral anionic site of butyrylcholinesterase. Mutants containing aromatic amino acids at the mouth of the gorge had increased binding affinity for propidium and fasciculin, but unaltered function, suggesting that aromatic amino acids are not important to the function of the peripheral anionic site of butyrylcholinesterase.
ESTHER : Masson_1996_Eur.J.Biochem_235_36
PubMedSearch : Masson_1996_Eur.J.Biochem_235_36
PubMedID: 8631355

Title : Peripheral Anionic Site of Wild-Type and Mutant Human Butyrylcholinesterase -
Author(s) : Masson P , Froment MT , Bartels CF , Lockridge O
Ref : In Enzyme of the Cholinesterase Family - Proceedings of Fifth International Meeting on Cholinesterases , (Quinn, D.M., Balasubramanian, A.S., Doctor, B.P., Taylor, P., Eds) Plenum Publishing Corp. :230 , 1995
PubMedID:

Title : Mutation His322Asn in human acetylcholinesterase does not alter electrophoretic and catalytic properties of the erythrocyte enzyme - Masson_1994_Blood_83_3003
Author(s) : Masson P , Froment MT , Sorenson RC , Bartels CF , Lockridge O
Ref : Blood , 83 :3003 , 1994
Abstract : The YT blood group antigen is located on human red blood cell (RBC) acetylcholinesterase. Wild-type acetylcholinesterase, YT1, has histidine at codon 322, whereas the genetic variant of acetylcholinesterase, YT2, has asparagine. This mutation is located within exon 2 of the ACHE gene, an exon that is present in all alternatively spliced forms of acetylcholinesterase. Therefore, acetylcholinesterase in brain and muscle has the same mutation as RBC acetylcholinesterase. We compared the electrophoretic and kinetic properties of RBC acetylcholinesterases having His 322 or Asn 322. We found no differences in the isoelectric point, mobility on non-denaturing gel electrophoresis, affinity for acetylthiocholine, activity per milligram of RBC ghost protein, substrate inhibition constants, binding to the peripheral site ligand (propidium), and binding to active site ligands (tetrahydroaminoacridine and edrophonium). Thus, although the point mutation elicits antibody production in nonmatching blood transfusion recipients, it has no effect on the enzymatic properties of acetylcholinesterase.
ESTHER : Masson_1994_Blood_83_3003
PubMedSearch : Masson_1994_Blood_83_3003
PubMedID: 8180397

Title : Poster: Molecular characterization of the C5 human plasma cholinesterase variant -
Author(s) : Masson P , Froment MT , Audras JC , Renault F
Ref : In: Cholinesterases: Structure, Function, Mechanism, Genetics, and Cell Biology , (Massoulie J, Barnard EA, Chatonnet A, Bacou F, Doctor BP, Quinn DM) American Chemical Society, Washington, DC :60 , 1991
PubMedID: