TISSUE TRANSGLUTAMINASE-CATALYZED FORMATION OF HIGH-MOLECULAR-WEIGHT AGGREGATES IN-VITRO IS FAVORED WITH LONG POLYGLUTAMINE DOMAINS - A POSSIBLE MECHANISM CONTRIBUTING TO CAG-TRIPLET DISEASES

To investigate possible biochemical mechanisms underlying the ''toxic gain of function'' associated with polyglutamine expansions, the abili ty of guinea pig liver tissue transglutaminase to catalyze covalent at tachments of various polyamines to polyglutamine peptides was examined . Of the polyamines tested, spermine is the most active substrate, fol lowed by spermidine and putrescine. Formation of covalent cross links between polyglutamine peptides and polyamines yields high-M-r aggregat es-a process that is favored with longer polyglutamines. In the presen ce of tissue transglutaminase, purified glyceraldehyde-3-phosphate deh ydrogenase (a key glycolytic enzyme that binds tightly to the polyglut amine domains of both huntingtin and dentatorubral-pallidoluysian atro phy proteins) is covalently attached to polyglutamine peptides in vitr o, resulting in the formation of high-M-r aggregates. In addition, end ogenous glyceraldehyde-3-phosphate dehydrogenase of a Balb-c 3T3 fibro blast cell line overexpressing human tissue transglutaminase forms cro ss-links with a Q(60) polypeptide added to the cell homogenate. Possib ly, expansion of polyglutamine domains (thus far known to occur in the gene products associated with at least seven neurodegenerative diseas es) leads to increased/aberrant tissue transglutaminase-catalyzed cros s-linking reactions with both polyamines and susceptible proteins, suc h as glyceraldehyde-3-phosphate dehydrogenase. Formation of cross-link ed heteropolymers may lead to deposition of high-M-r protein aggregate s, thereby contributing to cell death. (C) 1998 Academic Press.