Flashner Y

General

Full name : Flashner Yehuda

First name : Yehuda

Mail : Dept. of Biochemistry, Israel Inst. for BioI. Res., P.O.B. 19, 70450 Ness-Ziona

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Country : Israel

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Phone : (972) 8 381526

Fax : (972) 8 401094

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References (11)

Title : Signal-Mediated Cellular Retention and Subunit Assembly of Human Acetylcholinesterase -
Author(s) : Kronman C , Flashner Y , Shafferman A , Velan B
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. :293 , 1995
PubMedID:

Title : Post-Translation Processing of Acetylcholinesterase -
Author(s) : Velan B , Kronman C , Ordentlich A , Flashner Y , Ber R
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. :269 , 1995
PubMedID:

Title : Reversal of signal-mediated cellular retention by subunit assembly of human acetylcholinesterase - Velan_1994_J.Biol.Chem_269_22719
Author(s) : Velan B , Kronman C , Flashner Y , Shafferman A
Ref : Journal of Biological Chemistry , 269 :22719 , 1994
Abstract : The interrelationship between signal-mediated endoplasmic reticulum retention and control of subunit assembly in secreted complex proteins was examined in recombinant 293 cells expressing human acetylcholinesterase (HuAChE). This was achieved by analyzing the mutual effects of co-residing retention and dimerization signals on enzyme secretion by transfected cells. The function of putative signals within the COOH-terminal tetrapeptide CSDL of HuAChE was examined by site-directed mutagenesis. The CSDL tetrapeptide carries the free cysteine (Cys-580) involved in subunit assembly, yet it fails to function as a KDEL-type retention signal. This was demonstrated by mutations that increase similarity to the canonical retention signal (substitution of CSDL by KSDL) or those that deviate from it (substitution to CSAL). Cells expressing both types of mutants exhibited cell-associated HuAChE levels identical to that of wild type enzyme. Appendage of an engineered KDEL retention signal to a dimerization-impaired HuA-ChE subunit (the C580A mutant) resulted in intracellular retention of large amounts of fully active enzyme not prone to proteolytic degradation. On the other hand, attachment of KDEL to a native, dimerization-competent HuAChE polypeptide did not lead to intracellular retention and allowed efficient secretion of enzyme to the cell growth medium. Yet, appendage of KDEL to the native HuAChE led to some retardation in the transport of enzyme molecules through the Golgi apparatus, as manifested by increase in cellular population of endo H-resistant dimers, when compared with wild type enzyme. Taken together, these results indicate (alpha) that sub-unit dimerization mediated by the COOH-terminal cysteine of HuAChE can reverse the signal-mediated retention by masking recognition of KDEL by its cognate receptor and (b) that the native sequences of the acetylcholinesterase subunit polypeptide do not appear to function as a coupled retention/dimerization signal in the control of secretion of assembled enzyme molecules.
ESTHER : Velan_1994_J.Biol.Chem_269_22719
PubMedSearch : Velan_1994_J.Biol.Chem_269_22719
PubMedID: 8077224

Title : Dissection of the human acetylcholinesterase active center determinants of substrate specificity. Identification of residues constituting the anionic site, the hydrophobic site, and the acyl pocket - Ordentlich_1993_J.Biol.Chem_268_17083
Author(s) : Ordentlich A , Barak D , Kronman C , Flashner Y , Leitner M , Segall Y , Ariel N , Cohen S , Velan B , Shafferman A
Ref : Journal of Biological Chemistry , 268 :17083 , 1993
Abstract : Substrate specificity determinants of human acetylcholinesterase (HuAChE) were identified by combination of molecular modeling and kinetic studies with enzymes mutated in residues Trp-86, Trp-286, Phe-295, Phe-297, Tyr-337, and Phe-338. The substitution of Trp-86 by alanine resulted in a 660-fold decrease in affinity for acetythiocholine but had no effect on affinity for the isosteric uncharged substrate (3,3-dimethylbutylthioacetate). The results demonstrate that residue Trp-86 is the anionic site which binds, through cation-pi interactions, the quaternary ammonium of choline, and that of active center inhibitors such as edrophonium. The results also suggest that in the non-covalent complex, charged and uncharged substrates with a common acyl moiety (acetyl) bind to different molecular environments. The hydrophobic site for the alcoholic portion of the covalent adduct (tetrahedral intermediate) includes residues Trp-86, Tyr-337, and Phe-338, which operate through nonpolar and/or stacking interactions, depending on the substrate. Substrates containing choline but differing in the acyl moiety (acetyl, propyl, and butyryl) revealed that residues Phe-295 and Phe-297 determine substrate specificity of the acyl pocket for the covalent adducts. Phe-295 also determines substrate specificity in the non-covalent enzyme substrate complex and thus, the HuAChE F295A mutant exhibits over 130-fold increase in the apparent bimolecular rate constant for butyrylthiocholine compared with wild type enzyme. Reactivity toward specific butyrylcholinesterase inhibitors is similarly dependent on the nature of residues at positions 295 and 297. Amino acid Trp-286 at the rim of the active site "gorge" and Trp-86, in the active center, are essential elements in the mechanism of inhibition by propidium, a peripheral anionic site ligand. Molecular modeling and kinetic data suggest that a cross-talk between Trp-286 and Trp-86 can result in reorientation of Trp-86 which may then interfere with stabilization of substrate enzyme complexes. It is proposed that the conformational flexibility of aromatic residues generates a plasticity in the active center that contributes to the high efficiency of AChE and its ability to respond to external stimuli.
ESTHER : Ordentlich_1993_J.Biol.Chem_268_17083
PubMedSearch : Ordentlich_1993_J.Biol.Chem_268_17083
PubMedID: 8349597
Gene_locus related to this paper: human-ACHE , human-BCHE

Title : N-glycosylation of human acetylcholinesterase: effects on activity, stability and biosynthesis - Velan_1993_Biochem.J_296_649
Author(s) : Velan B , Kronman C , Ordentlich A , Flashner Y , Leitner M , Cohen S , Shafferman A
Ref : Biochemical Journal , 296 :649 , 1993
Abstract : The role of N-glycosylation in the function of human acetylcholinesterase (HuAChE) was examined by site-directed mutagenesis (Asn to Gln substitution) of the three potential N-glycosylation sites Asn-265, Asn-350 and Asn-464. Analysis of HuAChE mutants, defective in a single or multiple N-glycosylation sites, by expression in transiently or stably transfected human embryonal 293 kidney cells suggests the following. (a) All three AChE glycosylation signals are utilized, but not all the secreted molecules are fully glycosylated. (b) Glycosylation at all sites is important for effective biosynthesis and secretion; extracellular AChE levels in mutants defective in one, two or all three sites amounted to 20-30%, 2-4% and about 0.5% of wild-type level respectively. (c) Some glycosylation mutants display impaired stability, as reflected by increased susceptibility to heat inactivation; substitution of Asn-464 has the most pronounced effect on thermostability. (d) Abrogation of N-glycosylation has no detectable effect on the enzyme activity of HuAChE; all glycosylation mutants, including the triple mutant, hydrolyse acetylthiocholine efficiently, displaying Km, kcat. and kcat./Km values similar to those of the wild-type enzyme. (e) In most mutants, inhibition profiles with edrophonium and bisquaternary ammonium ligands are identical with those of wild-type enzyme; the Asn-350 mutants, however, exhibit a slight decrease in their affinity towards these ligands. (f) Elimination of oligosaccharide side chains has no detectable effect on the surface-related 'peripheral-site' functions; like the wild-type enzyme, all mutants were inhibited by propidium and by increased concentrations of acetylthiocholine.
ESTHER : Velan_1993_Biochem.J_296_649
PubMedSearch : Velan_1993_Biochem.J_296_649
PubMedID: 8280063

Title : Recombinant human acetylcholinesterase - Enzyme engineering -
Author(s) : Shafferman A , Velan B , Barak D , Kronman C , Ordentlich A , Flashner Y , Leitner M , Segal Y , Grosfeld H , Stein D , Ariel N
Ref : Medical Defense Bioscience Review , 3 :1097 , 1993
PubMedID:

Title : Mutagenesis of human acetylcholinesterase. Identification of residues involved in catalytic activity and in polypeptide folding - Shafferman_1992_J.Biol.Chem_267_17640
Author(s) : Shafferman A , Kronman C , Flashner Y , Leitner M , Grosfeld H , Ordentlich A , Gozes Y , Cohen S , Ariel N , Barak D , Harel M , Silman I , Sussman JL , Velan B
Ref : Journal of Biological Chemistry , 267 :17640 , 1992
Abstract : Evidence for the involvement of Ser-203, His-447, and Glu-334 in the catalytic triad of human acetylcholinesterase was provided by substitution of these amino acids by alanine residues. Of 20 amino acid positions mutated so far in human acetylcholinesterase (AChE), these three were unique in abolishing detectable enzymatic activity (less than 0.0003 of wild type), yet allowing proper production, folding, and secretion. This is the first biochemical evidence for the involvement of a glutamate in a hydrolase triad (Schrag, J.D., Li, Y., Wu, M., and Cygler, M. (1991) Nature 351, 761-764), supporting the x-ray crystal structure data of the Torpedo californica acetylcholinesterase (Sussman, J.L., Harel, M., Frolow, F., Oefner, C., Goldman, A., Toker, L. and Silman, I. (1991) Science 253, 872-879). Attempts to convert the AChE triad into a Cys-His-Glu or Ser-His-Asp configuration by site-directed mutagenesis did not yield effective AChE activity. Another type of substitution, that of Asp-74 by Gly or Asn, generated an active enzyme with increased resistance to succinylcholine and dibucaine; thus mimicking in an AChE molecule the phenotype of the atypical butyrylcholinesterase natural variant (D70G mutation). Mutations of other carboxylic residues Glu-84, Asp-95, Asp-333, and Asp-349, all conserved among cholinesterases, did not result in detectable alteration in the recombinant AChE, although polypeptide productivity of the D95N mutant was considerably lower. In contrast, complete absence of secreted human AChE polypeptide was observed when Asp-175 or Asp-404 were substituted by Asn. These two aspartates are conserved in the entire cholinesterase/thyroglobulin family and appear to play a role in generating and/or maintaining the folded state of the polypeptide. The x-ray structure of the Torpedo acetylcholinesterase supports this assumption by revealing the participation of these residues in salt bridges between neighboring secondary structure elements.
ESTHER : Shafferman_1992_J.Biol.Chem_267_17640
PubMedSearch : Shafferman_1992_J.Biol.Chem_267_17640
PubMedID: 1517212

Title : Substrate inhibition of acetylcholinesterase: residues affecting signal transduction from the surface to the catalytic center - Shafferman_1992_EMBO.J_11_3561
Author(s) : Shafferman A , Velan B , Ordentlich A , Kronman C , Grosfeld H , Leitner M , Flashner Y , Cohen S , Barak D , Ariel N
Ref : EMBO Journal , 11 :3561 , 1992
Abstract : Amino acids located within and around the 'active site gorge' of human acetylcholinesterase (AChE) were substituted. Replacement of W86 yielded inactive enzyme molecules, consistent with its proposed involvement in binding of the choline moiety in the active center. A decrease in affinity to propidium and a concomitant loss of substrate inhibition was observed in D74G, D74N, D74K and W286A mutants, supporting the idea that the site for substrate inhibition and the peripheral anionic site overlap. Mutations of amino acids neighboring the active center (E202, Y337 and F338) resulted in a decrease in the catalytic and the apparent bimolecular rate constants. A decrease in affinity to edrophonium was observed in D74, E202, Y337 and to a lesser extent in F338 and Y341 mutants. E202, Y337 and Y341 mutants were not inhibited efficiently by high substrate concentrations. We propose that binding of acetylcholine, on the surface of AChE, may trigger sequence of conformational changes extending from the peripheral anionic site through W286 to D74, at the entrance of the 'gorge', and down to the catalytic center (through Y341 to F338 and Y337). These changes, especially in Y337, could block the entrance/exit of the catalytic center and reduce the catalytic efficiency of AChE.
ESTHER : Shafferman_1992_EMBO.J_11_3561
PubMedSearch : Shafferman_1992_EMBO.J_11_3561
PubMedID: 1396557

Title : Production and secretion of high levels of recombinant human acetylcholinesterase in cultured cell lines: microheterogeneity of the catalytic subunit - Kronman_1992_Gene_121_295
Author(s) : Kronman C , Velan B , Gozes Y , Leitner M , Flashner Y , Lazar A , Marcus D , Sery T , Papier Y , Grosfeld H , Cohen S , Shafferman A
Ref : Gene , 121 :295 , 1992
Abstract : To allow for structural analysis of the human acetylcholinesterase (hAChE) subunit, a series of eukaryotic vectors was designed for efficient expression. Several eukaryotic multicistronic expression vectors were tested in various mammalian cell lines. All expression vectors contained the selectable neo gene under control of a weak promoter, while the hAChE cDNA was under control of the cytomegalovirus (CMV) immediate-early or Rous sarcoma virus long terminal repeat (RSV LTR) or simian virus 40 (SV40) early promoters. Optimal production and secretion of recombinant hAChE (rehAChE) was achieved in the embryonal kidney 293 cell line transfected either with the RSV-hAChE or with CMV-hAChE expression vectors. Clones expressing and secreting as much as 5-25 pg of enzyme per cell per 24 h were obtained without resorting to coamplification techniques or continuous maintenance of cells under selective pressure. The purified (specific activity of 6000 units per mg protein) homodimer and tetramer enzyme molecules displayed typical AChE biochemical properties: a Km value of 120 microM for acetylthiocholine; a kcat value of 3.9 x 10(5)/min, and selective by AChE-specific inhibitors. Catalytic subunit dimers (130 kDa) exhibit differential N-glycosylation patterns, and upon reduction resolve into 67- and 70-kDa monomeric subunits. These two forms appear as a single discrete 62-kDa band following deglycosylation by N-glycanase. The N-terminal amino acid sequence analysis of the purified mature enzyme suggests the existence of two alternative cleavage sites for the removal of the signal peptide, in which the 'mature' position 1 is either Ala31 or Gly33. Both of these positions conform with the consensus signal peptide recognition sequences and demonstrate bidirected processing of signal peptides on a native molecule.
ESTHER : Kronman_1992_Gene_121_295
PubMedSearch : Kronman_1992_Gene_121_295
PubMedID: 1446827

Title : The effect of elimination of intersubunit disulfide bonds on the activity, assembly, and secretion of recombinant human acetylcholinesterase. Expression of acetylcholinesterase Cys-580----Ala mutant - Velan_1991_J.Biol.Chem_266_23977
Author(s) : Velan B , Grosfeld H , Kronman C , Leitner M , Gozes Y , Lazar A , Flashner Y , Marcus D , Cohen S , Shafferman A
Ref : Journal of Biological Chemistry , 266 :23977 , 1991
Abstract : Site-directed mutagenesis was used to study the cysteine residue involved in the assembly of human acetylcholinesterase (HuAChE) catalytic subunits. Substitution of the cysteine at position 580 by alanine resulted in impairment of interchain disulfide bridge formation; the mutagenized enzyme (C580A) was secreted from recombinant cells in the monomeric form and failed to assemble into dimers. The mutant monomeric HuAChE did not differ from the native oligomeric enzyme neither in rate of catalysis nor in affinity to acetylthiocholine. Mutant monomers were also shown to retain the acetylcholinesterase characteristic sensitivity to high substrate concentrations. The mutation did not seem to affect the efficiencies of either synthesis or secretion of recombinant HuAChE polypeptides, as was demonstrated in cell lines derived from human embryonic kidney (293 cells) as well as from a human neuroblastoma (SK-N-SH). Furthermore, the mutation did not lead to an increase in accumulation of intracellular HuAChE polypeptides, suggesting that export of acetylcholinesterase from cells may not be coupled to subunit assembly.
ESTHER : Velan_1991_J.Biol.Chem_266_23977
PubMedSearch : Velan_1991_J.Biol.Chem_266_23977
PubMedID: 1748670

Title : Recombinant human acetylcholinesterase is secreted from transiently transfected 293 cells as a soluble globular enzyme - Velan_1991_Cell.Mol.Neurobiol_11_143
Author(s) : Velan B , Kronman C , Grosfeld H , Leitner M , Gozes Y , Flashner Y , Sery T , Cohen S , Ben-Aziz R , Seidman S , Shafferman A , Soreq H
Ref : Cellular Molecular Neurobiology , 11 :143 , 1991
Abstract : 1. Coding sequences for the human acetylcholinesterase (HuAChE; EC 3.1.1.7) hydrophilic subunit were subcloned in an expression plasmid vector under the control of cytomegalovirus IE gene enhancer-promoter. The human embryonic kidney cell line 293, transiently transfected with this vector, expressed catalytically active acetylcholinesterase. 2. The recombinant gene product exhibits biochemical traits similar to native "true" acetylcholinesterase as manifested by characteristic substrate inhibition, a Km of 117 microM toward acetylthiocholine, and a high sensitivity to the specific acetylcholinesterase inhibitor BW284C51. 3. The transiently transfected 293 cells (100 mm dish) produce in 24 hr active enzyme capable of hydrolyzing 1500 nmol acetylthiocholine per min. Eighty percent of the enzymatic activity appears in the cell growth medium as soluble acetylcholinesterase; most of the cell associated activity is confined to the cytosolic fraction requiring neither detergent nor high salt for its solubilization. 4. The active secreted recombinant enzyme appears in the monomeric, dimeric, and tetrameric globular hydrophilic molecular forms. 5. In conclusion, the catalytic subunit expressed from the hydrophilic AChE cDNA species has the inherent potential to be secreted in the soluble globular form and to generate polymorphism through self-association.
ESTHER : Velan_1991_Cell.Mol.Neurobiol_11_143
PubMedSearch : Velan_1991_Cell.Mol.Neurobiol_11_143
PubMedID: 1849451