title: Probing the stereochemistry of the active site of gamma-glutamyl transpeptidase using sulfur derivatives of l-glutamic acid.
abstract: Gamma-glutamyl transpeptidase (GGT) catalyses the transfer of a gamma-glutamyl moiety from a donor substrate to different acceptors, such as amino acids and water. GGT is known to display relatively low stereospecificity with respect to the alpha-stereocentre of its donor substrates. In this study we have studied its stereospecificity with respect to the stereocentre at the delta-position of different analogues of L-glutamic acid. Notably, L-methionine sulfoxide is well-recognised whereas L-methionine sulfone and L-methionine sulfoximine are not. Furthermore, when the synthetic gamma-diastereoisomers of L-methionine sulfoxide were separated and tested, it was discovered that GGT shows remarkable stereospecificity at the gamma-position, binding the S(C)S(S) diastereoisomer with a K(i) of 3.5 mM, whereas the S(C)R(S) diastereoisomer is not recognised. Finally, using a sulfoxide as a new pharmacophore for GGT, we have synthesized and tested an analogue of glutathione to obtain a very promising competitive inhibitor with a K(i) of (53 +/- 3) microM.
authors.affiliation: C. P. 6128, Succ. Centre-ville, Montréal, Québec H3C 3J7, Canada. keillorj@chimie.umontreal.ca
authors.forename: Christian
authors.initials: C
authors.lastname: Lherbet
authors.forename: Jeffrey W
authors.initials: JW
authors.lastname: Keillor
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D018698:Glutamic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D005978:Glutathione / Q000031:analogs & derivatives; D007700:Kinetics; D051381:Rats; D013237:Stereoisomerism; D013454:Sulfoxides / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D005723:gamma-Glutamyltransferase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D013454:Sulfoxides; D018698:Glutamic Acid; D005723:gamma-Glutamyltransferase; D005978:Glutathione