Mechanism for the inhibition of transglutaminase 2 by cystamine.
Cystamine is neuroprotective in a number of models of neurodegeneration. The therapeutic benefit of cystamine has been attributed, in part, to its inhibition of transglutaminase activity. Cystamine [beta-mercaptoethanolamine (MEA) disulfide] is reduced within cells to MEA which is largely responsible for the in vivo effects of its disulfide precursor. In the current study, the amine group of MEA was shown to act as a transglutaminase (TG) substrate resulting in the formation of N(beta)-(gamma-l-glutamyl)-MEA bonds. The formation of such bonds would compete with the generation of other TG-catalyzed reactions that may contribute to neurodegeneration such as polyamination, protein cross-linking, deamination and the covalent attachment of ceramide to proteins. The demonstration that cystamine-derived MEA can form N(beta)-(gamma-l-glutamyl)-MEA bonds offers a unique tool for identifying the TG substrates that occur in diseased brains in vivo. Structure-function studies also indicated that the mercapto group of MEA significantly influences the substrate behavior of this compound. These structure-function studies also identified the following hierarchy of physico-chemical characteristics: hydrophobicity > S as the group VIII atom > distance separating the N and group VIII atom, as the major determinants contributing to the substrate behavior for low-molecular weight amine substrates of TG 2.
Jeitner
Thomas M
TM
Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, USA. tjeitner@mcw.edu <tjeitner@mcw.edu>
Delikatny
E James
EJ
Ahlqvist
Jenny
J
Capper
Hugh
H
Cooper
Arthur J L
AJ
D000818:Animals; D001667:Binding, Competitive; D003538:Cystamine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006168:Guinea Pigs; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D013379:Substrate Specificity / Q000187:drug effects; D011503:Transglutaminases / Q000037:antagonists & inhibitors* / Q000378:metabolism
D004791:Enzyme Inhibitors; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins; D003538:Cystamine