Pesticides and warfare nerve agents are frequently organophosphates (OPs) or related compounds. Their acute toxicity highlighted more than ever the need to explore applicable strategies for the sensing, decontamination and/or detoxification of these compounds. Herein, we report the use of two different thermostable enzyme families capable to detect and inactivate OPs. In particular, mutants of carboxylesterase-2 from Alicyclobacillus acidocaldarius and of phosphotriesterase-like lactonases from Sulfolobus solfataricus and Sulfolobus acidocaldarius, have been selected and assembled in an optimized format for the development of an electrochemical biosensor and a decontamination formulation, respectively. The features of the developed tools have been tested in an ad-hoc fabricated chamber, to mimic an alarming situation of exposure to a nerve agent. Choosing ethyl-paraoxon as nerve agent simulant, a limit of detection (LOD) of 0.4 nM, after 5 s of exposure time was obtained. Furthermore, an optimized enzymatic formulation was used for a fast and efficient environmental detoxification (>99%) of the nebulized nerve agent simulants in the air and on surfaces. Crucial, large-scale experiments have been possible thanks to production of grams amounts of pure (>90%) enzymes.
In vitro evolution of enzymes represents a powerful device to evolve new or to improve weak enzymatic functions. In the present work a semi-rational engineering approach has been used to design an efficient and thermostable organophosphate hydrolase, starting from a lactonase scaffold (SsoPox from Sulfolobus solfataricus). In particular, by in vitro evolution of the SsoPox ancillary promiscuous activity, the triple mutant C258L/I261F/W263A has been obtained which, retaining its inherent stability, showed an enhancement of its hydrolytic activity on paraoxon up to 300-fold, achieving absolute values of catalytic efficiency up to 10(5) M(-1) s(-1) . The kinetics and structural determinants of this enhanced activity were thoroughly investigated and, in order to evaluate its potential biotechnological applications, the mutant was tested in formulations of different solvents (methanol or ethanol) or detergents (SDS or a commercial soap) for the cleaning of pesticide-contaminated surfaces. Biotechnol. Bioeng. 2016;113: 724-734. (c) 2015 Wiley Periodicals, Inc.
Title: Enlarging the substrate portfolio of the thermophilic esterase EST2 from Alicyclobacillus acidocaldarius Pennacchio A, Mandrich L, Manco G, Trincone A Ref: Extremophiles, 19:1001, 2015 : PubMed
The enzymatic regioselective hydrolysis of (a) acetylated mono- to tetrasaccharides of different nature, (b) of acetylated aryl glycosides and (c) of different acetylated nucleosides was studied enlarging the portfolio of substrates that can be employed by the thermophilic esterase EST2 from Alicyclobacillus acidocaldarius. The reactions were optimised to the extent that the amount of enzyme needed was lowered of two orders of magnitude with respect to the previously reported reactions, namely from 4000 to 40 U of enzyme per reaction. New additional solvents were screened and dramatic changes in regioselectivity were observed depending on the amount and type of solvent used. For example, in the presence of 10 % DMF, only two alpha-D-glucose products 6-OH and 4,6-OH (in a 76:24 ratio) were detected, whereas with 25 % DMF, at least four products of similar amount were observed. This versatility adds specific value to the biocatalyst making possible the design of biocatalytic reactions with different hydrophobic ester substrates. As an additional remarkable example, EST2 catalysed with a good yield and high regioselectivity the hydrolysis of p-nitrophenyl beta-D-xylopyranoside triacetate producing only the monoacetylated derivative with acetyl group in 3-O-position, in 2 min. The results with nucleosides as substrates are particularly interesting. The peracetates of 3',5'-di-O-acetylthymidine are converted almost quantitatively (95 %) to the monoacetylated derivative possessing free secondary OH; this regioselectivity is complementary to hydrolysis/alcoholysis reactions catalysed by CAL-B lipase or to other microbial hydrolytic biocatalysts, generally giving products with free primary OH groups. A docking analysis was undertaken with all analysed substrates suggesting a structural interpretation of the results. In most of cases, the best pose of the selected substrate was in line with the observed regioselectivity.
Title: A Further Biochemical Characterization of DrPLL the Thermophilic Lactonase from Deinococcus radiodurans Mandrich L, Di Gennaro S, Palma A, Manco G Ref: Protein Pept Lett, 20:36, 2013 : PubMed
Recently, the cloning of the ORF Dr0930 from Deinococcus radiodurans displaying, as primary activity, a lactonase activity and a promiscuous phosphotriesterase activity was reported. The crystal structure of the resulting recombinant enzyme has been solved, and many mutants have been generated in order to increase the phosphotriesterase activity, with the aim to reach the level of activity of the related pPTE from Pseudomonas diminuta. In this paper we report an additional biochemical characterization of DrPLL and show that this enzyme has an optimal temperature for catalysis of 85 C and possesses promiscuous carboxylesterase, phophodiesterase and thioesterase activities which were not previously described. A metal analysis was performed on the purified protein by inductively coupled plasma mass spectrometry (ICP-MS ELAN DRC-e), which confirmed the presence of Ni2+ as a main metal in the recombinant protein. Surprisingly, the specificity constants (s=kcat/KM) for the pNP-decanoate and pNP-dodecanoate esters were only one order of magnitude lower than that for the lactone substrate thio-buthyl-gamma-butyric-lactone (TBBL), and the KM value for TBBL was more than ten-fold higher than those for the esters. We named this enzyme DrPLL, based on its structural and biochemical features it belongs to the Phosphotriesterase Like Lactonase group, a small protein family belonging to the amidohydrolase superfamily.
Title: Comprehensive analysis of surface charged residues involved in thermal stability in Alicyclobacillus acidocaldarius esterase 2 Pezzullo M, Del Vecchio P, Mandrich L, Nucci R, Rossi M, Manco G Ref: Protein Engineering Des Sel, 26:47, 2013 : PubMed
Here we report a comprehensive analysis through alanine-scanning mutagenesis of the contribution of surface ion pairs to the thermal stability of Alicyclobacillus acidocaldarius esterase 2 (EST2). We produced 16 single mutants, 4 double mutants corresponding to selected ion pairs R31/E118, E43/K102, R58/D130, D145/R148, 2 double mutants (R63A/R98A and E50A/D94A) involving residues of a large ion network on the protein surface and the double-mutant R98A/R148A meant to disrupt the R98 interactions within the said network and, contextually, the interaction between R148 and D145. The double-mutant E43A/E273K was obtained by chance. All selected residues were replaced with alanine except E91, which was mutated to a glycine and K102, which was changed to a glutamine. All 24 proteins were over-expressed in Escherichia coli, purified and characterized with respect to the main features. Structural stability data were compared with an in silico prediction of DeltaDeltaG values. Our study of the individual factors involved in thermostability and their structural interpretation reveals that the great stability of this thermophilic protein can be explained by the contribution of a few residues at the protein surface.
The number of enzymes endowed with the capacity to catalyse other reactions than the main, physiological one, a feature that has been called promiscuity, is increasing at a fast pace. Promiscuity is a highly pervasive phenomenon that is present at each level of life complexity. For enzymes, promiscuity encompasses interesting aspects related to their physiological role, evolution and biotechnological applications. Herein, at first we will describe some general aspects of enzyme promiscuity and then we will report some examples from the alpha/beta hydrolase superfamily of proteins, with particular emphasis to the hormone-sensitive lipase family.
Cold-adapted esterases and lipases have been found to be dominant activities throughout the cold marine environment, indicating their importance in bacterial degradation of the organic matter. lip2 Gene from Psychrobacter sp. TA144, a micro-organism isolated from the Antarctic sea water, was cloned and over-expressed in Escherichia coli. The recombinant protein (PsyHSL) accumulated in the insoluble fraction from which it was recovered in active form, purified to homogeneity and deeply characterised. Temperature dependence of PsyHSL activity was typical of psychrophilic enzymes, with an optimal temperature of 35 degrees C at pH 8.0. The enzyme resulted to be active on pNP-esters of fatty acids with acyl chain length from C(2) to C(12) and the preferred substrate was pNP-pentanoate showing a k(cat) = 26.2 +/- 0.1 s(-1), K(M) = 0.122 +/- 0.006 mM and a k(cat)/K(M) = 215 +/- 11 mM(-1) s(-1). The enzyme was strongly inhibited by Hg(2+), Zn(2+), Cu(2+), Fe(3+), Mn(2+) ions and it resulted to be activated in presence of methanol and acetonitrile, with calculated C(50) values of 1.98 M and 0.92 M, respectively. The region surrounding PsyHSL catalytic site showed an unexpected homology with the human HSL. Further, both enzymes are characterised by the presence of an extra N-terminal domain, which role in the human protein has been related to regulative function. To clarify the function of PsyHSL N-terminal domain, a 97 amino acids deleted version of the enzyme was produced in E. coli in soluble form, purified and characterised. This mutant was inactive towards all tested substrates, indicating the involvement of this region in the catalytic process.
Title: Hyperthermophilic phosphotriesterases/lactonases for the environment and human health Mandrich L, Merone L, Manco G Ref: Environ Technol, 31:1115, 2010 : PubMed
In the last decades the idea to use enzymes for environmental bioremediation has been more and more proposed and, in the light of this, new solutions have been suggested and detailed studies on some classes of enzymes have been performed. In particular, our attention in the last few years has been focused on the enzymes belonging to the amidohydrolase superfamily. Several members of this superfamily are endowed with promiscuous activities. The term 'catalytic promiscuity' describes the capability of an enzyme to catalyse different chemical reactions, called secondary activities, at the active site responsible for the main activity. Recently, a new family of microbial lactonases with promiscuous phosphotriesterase activity, dubbed PTE-Like Lactonase (PLL), has been ascribed to the amidohydrolase superfamily. Among members of this family are enzymes found in the archaea Sulfolobus solfataricus and Sulfolobus acidocaldarius, which show high thermophilicity and thermal resistance. Enzymes showing phosphotriesterase activity are attractive from a biotechnological point of view because they are capable of hydrolysing the organophosphate phosphotriesters (OPs), a class of synthetic compounds employed worldwide both as insecticides and chemical warfare agents. Furthermore, from a basic point of view, studies of catalytic promiscuity offer clues to understand natural evolution of enzymes and to translate this into in vitro adaptation of enzymes to specific human needs. Thermostable enzymes able to hydrolyse OPs are considered good candidates for the set-up of efficient detoxification tools.
The thermostable Phosphotriesterase-Like Lactonase from Sulfolobus solfataricus (SsoPox) hydrolyzes lactones and, at a lower rate, neurotoxic organophosphorus compounds. The persistent demand of detoxification tools in the field of agricultural wastes and restoring of conditions after terrorist acts prompted us to exploit SsoPox as a "starter" to evolve its ancillary nerve agents hydrolytic capability. A directed evolution strategy yielded, among several variants, the single mutant W263F with k(cat) and specificity constant against paraoxon 16- and 6-fold enhanced, respectively, compared to the wild type. Furthermore, a phenomenon of enzyme activation by SDS has been observed, which allowed to increase those values 150- and 28-fold, respectively. The activity of SsoPox against the deadly nerve gas Cyclosarin has been reported for the first time and proved to be substantially unaffected for variant W263F. Finally, outperforming efficiency of W263F was demonstrated, under severe stressing conditions, with respect to the best known phosphotriesterase PTE from Brevundimonas diminuta.
Title: Evolution in the amidohydrolase superfamily: substrate-assisted gain of function in the E183K mutant of a phosphotriesterase-like metal-carboxylesterase Mandrich L, Manco G Ref: Biochemistry, 48:5602, 2009 : PubMed
The recent specialization for utilization of pesticides reported for Pseudomonas diminuta phosphotriesterase (pPTE) strongly suggests that this activity evolved from an enzyme endowed with promiscuous phosphotriesterase activity. Such a putative "generalist" enzyme was recently proposed to be a member of the new phoshotriesterase-like lactonase family (PLL). The promiscuous carboxylesterase and phosphodiesterase activities detected in pPTE and PLLs in turn paved the way for the prediction of the existence in nature of PTE-like enzymes with predominant carboxylesterase or phosphodiesterase activities. An "in silico" analysis of the related Mesorhizobium loti ORF MLL7664 and the biochemical characterization demonstrated its prominent carboxylesterase and low phosphotriesterase specificity. On the basis of sequence similarity with the phosphotriesterase homology protein from Escherichia coli and the carboxylesterase activity, we called it phosphotriesterase-like carboxylesterase (MloPLC). The carboxylesterase activity is strictly dependent on divalent cations, and as such MloPLC is the first phosphotriesterase-like metal-carboxylesterase characterized to date. In related enzymes of the amidohydrolase superfamily either glutamate or carboxylated lysine substitutes for MloPLC glutamate 183 and the residue appear invariantly involved in maintaining the structural integrity of the binuclear metal center. Accordingly, we changed Glu-183 to lysine or glutamine. All the tested activities were completely abolished in the E183Q mutant, while only a residual phosphotriesterase activity could be detected in the E183K mutant. Surprisingly, in the latter mutant a parallel 650-fold specificity increase in bis-p-nitrophenyl-phosphate (BpNP-P) was observed, turning MloPLC from a carboxylesterase into a phosphodiesterase. Chemical, structural, and kinetic data strongly suggested that K183 is not carboxylated and that the gain of the new function is assisted by the substrate.
Title: Structural and kinetic overview of the carboxylesterase EST2 from alicyclobacillus acidocaldarius: a comparison with the other members of the HSL family Mandrich L, Merone L, Manco G Ref: Protein Pept Lett, 16:1189, 2009 : PubMed
Thermophilic and hyperthermophilic carboxylesterases (EC 3.1.1.1) are excellent model systems for studying structure function relationships as well as in vitro and in vivo evolution and possible biotechnological applications. In this paper we review the main aspect of one of most studied microbial representative of the hormone sensitive lipase family (HSL), namely carboxylesterase 2 (EST2) from Alicyclobacillus acidocaldarius.
Organophosphates are the largest class of known insecticides, several of which are potent nerve agents. Consequently, organophosphate-degrading enzymes are of great scientific interest as bioscavengers and biodecontaminants. Recently, a hyperthermophilic phosphotriesterase (known as SsoPox), from the Archaeon Sulfolobus solfataricus, has been isolated and found to possess a very high lactonase activity. Here, we report the three-dimensional structures of SsoPox in the apo form (2.6 A resolution) and in complex with a quorum-sensing lactone mimic at 2.0 A resolution. The structure also reveals an unexpected active site topology, and a unique hydrophobic channel that perfectly accommodates the lactone substrate. Structural and mutagenesis evidence allows us to propose a mechanism for lactone hydrolysis and to refine the catalytic mechanism established for phosphotriesterases. In addition, SsoPox structures permit the correlation of experimental lactonase and phosphotriesterase activities and this strongly suggests lactonase activity as the cognate function of SsoPox. This example demonstrates that promiscuous activities probably constitute a large and efficient reservoir for the creation of novel catalytic activities.
Kinetic studies of irreversible inhibition in recent years have received growing attention owing to their relevance to problems of basic scientific interest as well as to their practical importance. Our studies have been devoted to the characterization of the effects that well-known acetylcholinesterase irreversible inhibitors exert on a carboxylesterase (EST2) from the thermophilic eubacterium Alicyclobacillus acidocaldarius. In particular, sulfonyl inhibitors and the organophosphorous insecticide diethyl-p-nitrophenyl phosphate (paraoxon) have been studied. The incubation of EST2 with sulfonyl inhibitors resulted in a time-dependent inactivation according to a pseudo-first-order kinetics. On the other hand, the EST2 inactivation process elicited by paraoxon, being the inhibition reaction completed immediately after the inhibitor addition, cannot be described as a pseudo-first-order kinetics but is better considered as a high affinity inhibition. The values of apparent rate constants for paraoxon inactivation were determined by monitoring the enzyme/substrate reaction in the presence of the inhibitor, and were compared with those of the sulfonyl inhibitors. The protective effect afforded by a competitive inhibitor on the EST2 irreversible inhibition, and the reactivation of a complex enzyme/irreversible-inhibitor by hydroxylamine and 2-PAM, were also investigated. The data have been discussed in the light of the recently described dual substrate binding mode of EST2, considering that the irreversible inhibitors employed were able to discriminate between the two different binding sites.
Recent mutagenic and molecular modelling studies suggested a role for glycine 84 in the putative oxyanion loop of the carboxylesterase EST2 from Alicyclobacillus acidocaldarius. A 114 times decrease of the esterase catalytic activity of the G84S mutant was observed, without changes in the thermal stability. The recently solved three-dimensional (3D) structure of EST2 in complex with a HEPES molecule permitted to demonstrate that G84 (together with G83 and A156) is involved in the stabilization of the oxyanion through a hydrogen bond from its main chain NH group. The structural data in this case did not allowed us to rationalize the effect of the mutation, since this hydrogen bond was predicted to be unaltered in the mutant. Since the mutation could shed light on the role of the oxyanion loop in the HSL family, experiments to elucidate at the mechanistic level the reasons of the observed drop in k (cat) were devised. In this work, the kinetic and structural features of the G84S mutant were investigated in more detail. The optimal temperature and pH for the activity of the mutated enzyme were found significantly changed (T = 65 degrees C and pH = 5.75). The catalytic constants K (M) and V(max) were found considerably altered in the mutant, with ninefold increased K (M) and 14-fold decreased V(max), at pH 5.75. At pH 7.1, the decrease in k (cat) was much more dramatic. The measurement of kinetic constants for some steps of the reaction mechanism and the resolution of the mutant 3D structure provided evidences that the observed effects were partly due to the steric hindrance of the S84-OH group towards the ester substrate and partly to its interference with the nucleophilic attack of a water molecule on the second tetrahedral intermediate.
Title: SSoNDelta and SSoNDeltalong: two thermostable esterases from the same ORF in the archaeon Sulfolobus solfataricus? Mandrich L, Pezzullo M, Rossi M, Manco G Ref: Archaea, 2:109, 2007 : PubMed
Previously, we reported from the Sulfolobus solfataricus open reading frame (ORF) SSO2517 the cloning, overexpression and characterization of an esterase belonging to the hormone-sensitive lipase (HSL) family and apparently having a deletion at the N-terminus, which we named SSoNDelta. Searching the recently reported Sulfolobus acidocaldarius genome by sequence alignment, using SSO2517 as a query, allowed identity of a putative esterase (ORF SAC1105) sharing high sequence similarity (82%) with SSO2517. This esterase displays an N-terminus and total length similar to other known esterases of the HSL family. Analysis of the upstream DNA sequence of SS02517 revealed the possibility of expressing a longer version of the protein with an extended N-terminus; however, no clear translation signal consistent with a longer protein version was detected. This new version of SSO2517 was cloned, over-expressed, purified and characterized. The resulting protein, named SSoNDeltalong, was 15-fold more active with the substrate p-nitrophenyl hexanoate than SSoNDelta. Furthermore, SSoNDeltalong and SSoNDelta displayed different substrate specificities for triacylglycerols. These results and the phylogenetic relationship between S. solfataricus and S. acidocaldarius suggest a common origin of SSO2517 and SAC1105 from an ancestral gene, followed by divergent evolution. Alternatively, a yet-to-be discovered mechanism of translation that directs the expression of SSoNDeltalong under specific metabolic conditions could be hypothesized.
Title: A new phosphotriesterase from Sulfolobus acidocaldarius and its comparison with the homologue from Sulfolobus solfataricus Porzio E, Merone L, Mandrich L, Rossi M, Manco G Ref: Biochimie, 89:625, 2007 : PubMed
The phosphotriesterase PTE, identified in the soil bacterium Pseudomonas diminuta, is thought to have evolved in the last several decades to degrade the pesticide paraoxon with proficiency approaching the limit of substrate diffusion (k(cat)/K(M) of 4 x 10(7)M(-1)s(-1)). It belongs to the amidohydrolase superfamily, but its evolutionary origin remains obscure. The enzyme has important potentiality in the field of the organophosphate decontamination. Recently we reported on the characterization of an archaeal member of the amidohydrolase superfamily, namely Sulfolobus solfataricus, showing low but significant and extremely thermostable paraoxonase activity (k(cat)/K(M) of 4 x 10(3)M(-1)s(-1)). Looking for other thermostable phosphotriesterases we assayed, among others, crude extracts of Sulfolobus acidocaldarius and detected activity. Since the genome of S. acidocaldarius has been recently reported, we identified there an open reading frame highly related to the S. solfataricus enzyme. The gene was cloned, the protein overexpressed in Escherichia coli, purified, and proven to have paraoxonase activity. A comparative analysis detected some significant differences between the two archaeal enzymes.
Hormone-sensitive lipase (HSL) contributes importantly to the mobilization of fatty acids from the triacylglycerols stored in adipocytes, which provide the main source of energy in mammals. On the basis of amino acid sequence alignments and three-dimensional structures, this enzyme was previously found to be a suitable template for defining a family of serine carboxylester hydrolases. In this study, the HSL family members are characterized rather on the basis of their inhibition by 5-methoxy-3-(4-phenoxyphenyl)-3H-[1,3,4]oxadiazol-2-one (compound 7600). This compound inhibits mammalian HSL as well as other HSL family members, such as EST2 from the thermophilic eubacterium Alicyclobacillus acidocaldarius and AFEST from the hyperthermophilic archaeon Archaeoglobus fulgidus. Various carboxylester hydrolases that are not members of the HSL family were found not to be inhibited by compound 7600 under the same experimental conditions. These include nonlipolytic hydrolases such as Torpedo californica acetylcholinesterase and pig liver esterase, as well as lipolytic hydrolases such as human pancreatic lipase, dog gastric lipase, Thermomyces lanuginosus lipase, and Bacillus subtilis LipA. When vinyl esters were used as substrates, the residual activity of HSL, AFEST, and EST2 decreased with an increase in compound 7600 concentration in the incubation mixture. The inhibitor concentration at which the enzyme activity decreased to 50% after incubation for 5 min was 70, 20, and 15 nM with HSL, AFEST, and EST2, respectively. Treating EST2 and AFEST with the inhibitor resulted in an increase in the molecular mass, as established by performing matrix-assisted laser desorption ionization time-of-flight mass spectrometry analysis. This increase in the molecular mass, which corresponds approximately to the molecular mass of the inhibitor, indicates that a covalent enzyme-inhibitor complex has been formed. Surface-enhanced laser desorption ionization time-of-flight mass spectrometry analysis of a trypsin digest of AFEST treated with the inhibitor or not treated showed the occurrence of an increase in the molecular masses of the "GESAGG"-containing peptide, which is compatible with the formation of a covalent complex with the inhibitor.
The aim of this work was to investigate the behavior of thermophilic esterase EST2 from Alicyclobacillus acidocaldarius in milk and cheese models. The pure enzyme was used to compare the EST2 hydrolytic activity to the activity of endogenous esterase EstA from Lactococcus lactis. The results indicate that EST2 exhibits 30-fold-higher esterase activity than EstA. As EstA has thioesterase activity, EST2 was assayed for this activity under the optimal conditions determined for EstA (namely, 30 degrees C and pH 7.5). Although it is a thermophilic enzyme, EST2 exhibited eightfold-higher thioesterase activity than EstA with S-methyl thiobutanoate. The abilities of EST2 and EstA to synthesize short-chain fatty acid esters were compared. Two methods were developed to do this. In the first method a spectrophotometric assay was used to monitor the synthesis of esters by the pure enzymes using p-nitrophenol as the alcohol substrate. The synthetic activities were also evaluated under conditions that mimicked those present in milk and/or cheese. The second method involved evaluation of the synthetic abilities of the enzymes when they were directly added to a model cheese matrix. Substantial ester synthesis by EST2 was observed under both conditions. Finally, esterase and thioesterase activities were evaluated in milk using the purified EST2 enzyme and in the model cheese matrix using a strain of L. lactis NZ9000 harboring the EST2 gene and thus overproducing EST2. Both the esterase and thioesterase activities measured in milk and in the cheese matrix were much greater than the activities of the controls.
Title: Substrate specificity and kinetic properties of enzymes belonging to the hormone-sensitive lipase family: comparison with non-lipolytic and lipolytic carboxylesterases Chahinian H, Ben Ali Y, Abousalham A, Petry S, Mandrich L, Manco G, Canaan S, Sarda L Ref: Biochimica & Biophysica Acta, 1738:29, 2005 : PubMed
We have studied the kinetics of hydrolysis of triacylglycerols, vinyl esters and p-nitrophenyl butyrate by four carboxylesterases of the HSL family, namely recombinant human hormone-sensitive lipase (HSL), EST2 from Alicyclobacillus acidocaldarius, AFEST from Archeoglobus fulgidus, and protein RV1399C from Mycobacterium tuberculosis. The kinetic properties of enzymes of the HSL family have been compared to those of a series of lipolytic and non-lipolytic carboxylesterases including human pancreatic lipase, guinea pig pancreatic lipase related protein 2, lipases from Mucor miehei and Thermomyces lanuginosus, cutinase from Fusarium solani, LipA from Bacillus subtilis, porcine liver esterase and Esterase A from Aspergilus niger. Results indicate that human HSL, together with other lipolytic carboxylesterases, are active on short chain esters and hydrolyze water insoluble trioctanoin, vinyl laurate and olive oil, whereas the action of EST2, AFEST, protein RV1399C and non-lipolytic carboxylesterases is restricted to solutions of short chain substrates. Lipolytic and non-lipolytic carboxylesterases can be differentiated by their respective value of K(0.5) (apparent K(m)) for the hydrolysis of short chain esters. Among lipolytic enzymes, those possessing a lid domain display higher activity on tributyrin, trioctanoin and olive oil suggesting, then, that the lid structure contributes to enzyme binding to triacylglycerols. Progress reaction curves of the hydrolysis of p-nitrophenyl butyrate by lipolytic carboxylesterases with lid domain show a latency phase which is not observed with human HSL, non-lipolytic carboxylesterases, and lipolytic enzymes devoid of a lid structure as cutinase.
A superposition between the structures of Alicyclobacillus acidocaldarius esterase 2 (EST2) and Burkholderia cepacia lipase, the latter complexed with a phosphonate inhibitor, allowed us to hypothesize for the EST2 N terminus a role in restricting the access to the active site and therefore in modulating substrate specificity. In order to test this hypothesis we generated by site-directed mutagenesis some truncated versions of EST2 and its double mutant M211S/R215L (S/L) at the N terminus. In parallel, an analysis of the Sulfolobus solfataricus P2 genome allowed us to identify a gene coding for a putative esterase of the HSL family having a natural deletion of the corresponding region. The product of this gene and the above-mentioned EST2 mutants were expressed in Escherichia coli, purified and characterised. These studies support the notion that the N terminus affects substrate specificity other than several other enzyme parameters. Although the deletions afforded a tenfold and 550-fold decrease in catalytic efficiency towards the best substrate pNP-hexanoate at 50 degrees C for EST2 and S/L, respectively, the analysis of the specific activities with different triacylglycerols with respect to pNP-hexanoate showed that their ratios were higher for deleted versus non-deleted enzymes, on all tested substrates. In particular, the above ratios for glyceryl tridecanoate were 30-fold and 14-fold higher in S/L and EST2 deleted forms, respectively, compared with their full-length versions. This behaviour was confirmed by the analysis of the S.solfataricus esterase, which showed similar specific activities on pNP-hexanoate and triacylglycerols; in addition, higher activities on the latter substrates were observed in comparison with EST2, S/L and their deleted forms. Finally, a dramatic effect on thermophilicity and thermostability in the EST2 deleted forms was observed. This is the first report highlighting the importance of the "cap" domain in the HSL family, since the N terminus partly contributes to the building up of this structure.
The reaction mechanism of the esterase 2 (EST2) from Alicyclobacillus acidocaldarius was studied at the kinetic and structural level to shed light on the mechanism of activity and substrate specificity increase previously observed in its double mutant M211S/R215L. In particular, the values of kinetic constants (k1, k(-1), k2, and k3) along with activation energies (E1, E(-1), E2, and E3) were measured for wild type and mutant enzyme. The previously suggested substrate-induced switch in the reaction mechanism from kcat=k3 with a short acyl chain substrate (p-nitrophenyl hexanoate) to kcat=k2 with a long acyl chain substrate (p-nitrophenyl dodecanoate) was validated. The inhibition afforded by an irreversible inhibitor (1-hexadecanesulfonyl chloride), structurally related to p-nitrophenyl dodecanoate, was studied by kinetic analysis. Moreover the three-dimensional structure of the double mutant bound to this inhibitor was determined, providing essential information on the enzyme mechanism. In fact, structural analysis explained the observed substrate-induced switch because of an inversion in the binding mode of the long acyl chain derivatives with respect to the acyl- and alcohol-binding sites.
Esterase 2 (EST2) from the thermophilic eubacterium Alicyclobacillus acidocaldarius is a thermostable serine hydrolase belonging to the H group of the esterase/lipase family. This enzyme hydrolyzes monoacylesters of different acyl-chain length and various compounds with industrial interest. EST2 displays an optimal temperature at 70 degrees C and maximal activity with pNP-esters having acyl-chain bearing from six to eight carbon atoms. EST2 mutants with different substrate specificity were also designed, generated by site-directed mutagenesis, and biochemically characterized. To better define at structural level the enzyme reaction mechanism, a crystallographic analysis of one of these mutants, namely M211S/R215L, was undertaken. Here we report its three-dimensional structure at 2.10A resolution. Structural analysis of the enzyme revealed an unexpected dimer formation as a consequence of a domain-swapping event involving its N-terminal region. This phenomenon was absent in the case of the enzyme bound to an irreversible inhibitor having optimal substrate structural features. A detailed comparison of the enzyme structures before and following binding to this molecule showed a movement of the N-terminal helices resulting from a trans-cis isomerization of the F37-P38 peptide bond. These findings suggest that this carboxylesterase presents two distinct structural arrangements reminiscent of the open and closed forms already reported for lipases. Potential biological implications associated with the observed quaternary reorganization are here discussed in light of the biochemical properties of other lipolytic members of the H group.
The recently solved three-dimensional (3D) structures of two thermostable members of the carboxylesterase/lipase HSL family, namely the Alicyclobacillus (formerly Bacillus) acidocaldarius and Archaeoglobus fulgidus carboxylesterases (EST2 and AFEST, respectively) were compared with that of the mesophilic homologous counterpart Brefeldine A esterase from Bacillus subtilis. Since the 3D homology models of other members of the HSL family were also available, we performed a structural alignment with all these sequences. The resulting alignment was used to assess the amino acid "traffic rule" in the HSL family. Quite surprisingly, the data were in very good agreement with those recently reported from two independent groups and based on the comparison of a huge number of homologous sequences from the genus Bacillus, Methanococcus and Deinococcus/Thermus. Taken as a whole, the data point to the statistical meaning of defined amino acid conversions going from psychrophilic to hyperthermophilic sequences. We identified and mapped several such changes onto the EST2 structure and observed that such mutations were localized mostly in loops regions or alpha-helices and were mostly excluded from the active site. A site-directed mutagenesis of two of the identified residues confirmed they were involved in thermal stability.
The conformational stability of the hyperthermophilic esterase AFEST from Archeoglobus fulgidus against the denaturing action of 2,2,2-trifluoroethanol (TFE) has been investigated by means of circular dichroism (CD) measurements. At room temperature far-UV and near-UV CD spectra point out the occurrence of a co-operative transition from the native structure to a denatured state characterized by a high content of alpha-helix. The TFE concentration at half-completion of the transition proves to be 3.5 M (25% v v(-1)), by recording the molar ellipticity at both 222 and 276 nm. Thermal transition curves of AFEST in the absence and in the presence of TFE indicate a significant stability decrease on increasing the TFE concentration. The denaturation temperature is 99 degrees C for native AFEST, but becomes 85 degrees C at 1.4 M TFE (10% v v(-1)), and 56 degrees C at 2.8 M TFE (20% v v(-1)). It is also shown that, even though AFEST is very resistant to temperature, its resistance towards the denaturing action of TFE is similar to that of mesophilic proteins, including an esterase from Escherichia coli, AES. The proposal of a general mechanism for the TFE action on globular proteins leads to a reliable rationale of experimental data.
The acetyl-esterase Aes from Escherichia coli, which belongs to the HSL group of the esterase/lipase superfamily, has been crystallized by the hanging-drop vapour-diffusion method using polyethylene glycol 8000 as a precipitant and magnesium chloride as an additive. Crystals belong to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 110.0, b = 190.6, c = 218.6 A. A complete data set has been collected to 2.5 A resolution at the Elettra synchrotron source, Trieste using a single frozen crystal. Packing density considerations agree with 10-16 monomers in the asymmetric unit, with a corresponding solvent content of 61-38%.
Title: The Aes protein and the monomeric alpha-galactosidase from Escherichia coli form a non-covalent complex. Implications for the regulation of carbohydrate metabolism Mandrich L, Caputo E, Martin BM, Rossi M, Manco G Ref: Journal of Biological Chemistry, 277:48241, 2002 : PubMed
Aes, a 36-kDa acetylesterase from Escherichia coli, belongs to the hormone-sensitive lipase family, and it is involved in the regulation of MalT, the transcriptional activator of the maltose regulon. The activity of MalT is depressed through a direct protein-protein interaction with Aes. Although the effect is clear-cut, the meaning of this interaction and the conditions that trigger it still remain elusive. To perform a comparative thermodynamic study between the mesophilic Aes protein and two homologous thermostable enzymes, Aes was overexpressed in E. coli and purified. At the last step of the purification procedure the enzyme was eluted from a Mono Q HR 5/5 column as a major form migrating, anomalously, at 56 kDa on a calibrated Superdex 75 column. A minor peak that contains the Aes protein and a polypeptide of 50 kDa was also detected. By a combined analysis of size-exclusion chromatography and surface-enhanced laser desorption ionization-time of flight mass spectrometry, it was possible to demonstrate the presence in this peak of a stable 87-kDa complex, containing the Aes protein itself and the 50-kDa polypeptide in a 1:1 ratio. The homodimeric molecular species of Aes and of the 50-kDa polypeptide were also detected. The esterase activity associated with the 87-kDa complex, when assayed with p-nitrophenyl butanoate as substrate, proved 6-fold higher than the activity of the major Aes form of 56 kDa. Amino-terminal sequencing highlighted that the 50-kDa partner of Aes in the complex was the alpha-galactosidase from E. coli. The E. coli cells harboring plasmid pT7-SCII-aes and, therefore, expressing Aes were hampered in their growth on a minimal medium containing raffinose as a sole carbon source. Because alpha-galactosidase is involved in the metabolism of raffinose, the above findings suggest a potential role of Aes in the regulation of carbohydrate metabolism in E. coli.
The crystal structure of AFEST, a novel hyper-thermophilic carboxylesterase from the archaeon Archaeoglobus fulgidus, complexed with a sulphonyl derivative, has been determined and refined to 2.2 A resolution. This enzyme, which has recently been classified as a member of the hormone- sensitive-lipase (H) group of the esterase/lipase superfamily, presents a canonical alpha/beta hydrolase core, shielded on the C-terminal side by a cap region composed of five alpha-helices. It contains the catalytic triad Ser160, His285 and Asp255, whereby the nucleophile is covalently modified and the oxyanion hole formed by Gly88, Gly89 and Ala161. A structural comparison of AFEST with its mesophilic and thermophilic homologues, Brefeldin A esterase from Bacillus subtilis (BFAE) and EST2 from Alicyclobacillus acidocaldarius, reveals an increase in the number of intramolecular ion pairs and secondary structure content, as well as a significant reduction in loop extensions and ratio of hydrophobic to charged surface area. The variety of structural differences suggests possible strategies for thermostabilization of lipases and esterases with potential industrial applications.
Title: Residues at the active site of the esterase 2 from Alicyclobacillus acidocaldarius involved in substrate specificity and catalytic activity at high temperature Manco G, Mandrich L, Rossi M Ref: Journal of Biological Chemistry, 276:37482, 2001 : PubMed
The recently solved three-dimensional structure of the thermophilic esterase 2 from Alicyclobacillus acidocaldarius allowed us to have a snapshot of an enzyme-sulfonate complex, which mimics the second stage of the catalytic reaction, namely the covalent acyl-enzyme intermediate. The aim of this work was to design, by structure-aided analysis and to generate by site-directed and saturation mutagenesis, EST2 variants with changed substrate specificity in the direction of preference for monoacylesters whose acyl-chain length is greater than eight carbon atoms. Positions 211 and 215 of the polypeptide chain were chosen to introduce mutations. Among five variants with single and double amino acid substitutions, three were obtained, M211S, R215L, and M211S/R215L, that changed the catalytic efficiency profile in the desired direction. Kinetic characterization of mutants and wild type showed that this change was achieved by an increase in k(cat) and a decrease in K(m) values with respect to the parental enzyme. The M211S/R215L specificity constant for p-nitrophenyl decanoate substrate was 6-fold higher than the wild type. However, variants M211T, M211S, and M211V showed strikingly increased activity as well as maximal activity with monoacylesters with four carbon atoms in the acyl chain, compared with the wild type. In the case of mutant M211T, the k(cat) for p-nitrophenyl butanoate was 2.4-fold higher. Overall, depending on the variant and on the substrate, we observed improved catalytic activity at 70 degrees C with respect to the wild type, which was a somewhat unexpected result for an enzyme with already high k(cat) values at high temperature. In addition, variants with altered specificity toward the acyl-chain length were obtained. The results were interpreted in the context of the EST2 three-dimensional structure and a proposed catalytic mechanism in which k(cat), e.g. the limiting step of the reaction, was dependent on the acyl chain length of the ester substrate.
