OLIGOMERIZATION OF HAMSTER UDP-GLCNAC-DOLICHOL-P GLCNAC-1-P TRANSFERASE, AN ENZYME WITH MULTIPLE TRANSMEMBRANE SPANS

Hamster UDP-GlcNAc:dolichol-P GlcNAc-1-P transferase (GPT), which init iates N-linked glycosylation by catalyzing the synthesis of GlcNAc-P-P -dolichol, has multiple transmembrane spans and a catalytic site that probably exists on the cytosolic face of the endoplasmic reticulum mem brane (Dan, N., Middleton, R. M., and Lehrman, M. A. (1996) J. Biol. C hem. 271, 30717-30725), In this report, we demonstrate that GPT forms functional oligomers, probably dimers, Oligomers were detected by chem ical cross-linking of GPT and by a dominant-negative effect caused by co-expression of enzymatically inactive (but properly folded) GPT muta nts, The GPT mutants had no effect on two other dolichol-P-dependent e ndoplasmic reticulum enzymes, Mixing experiments indicated that mature GPT was competent for oligomerization. Oligomerization appeared to be favored in detergent extracts compared with intact microsomes. Deterg ent treatments were found to prevent, rather than promote, nonspecific aggregation of GPT, These results demonstrate that GPT subunits can p hysically interact and influence each other, The implications of oligo merization for enzyme function are discussed, From these results, we c onclude that GPT is one of a very small number of multitransmembrane s pan enzymes that can form multimers.