Journal
CHEMISTRY & BIOLOGY
Volume 11, Issue 12, Pages 1677-1687Publisher
CELL PRESS
DOI: 10.1016/j.chembiol.2004.11.010
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Peptide:N-glycanase (PNGase) is ostensibly the sole enzyme responsible for deglycosylation of unfolded N-linked glycoproteins dislocated from the ER to the cytosol. Here we show the pan-caspase inhibitor, Z-VAD-fmk, to be an active site-directed irreversible inhibitor of yeast and mammalian PNGase at concentrations below those used to inhibit caspases in vivo. Through chemical synthesis we determined that the P-1 residue, electrophile position, and leaving group are important structural parameters for PNGase inhibition. We show that Z-VAD-fmk inhibits PNGase in living cells and that degradation of class I MHC heavy chains and TCRalpha, in an identical cellular setting, is markedly different. Remarkably, proteasome-mediated turnover of class I MHC heavy chains proceeds even when PNGase is completely inhibited, suggesting that the function of PNGase may be to facilitate more efficient proteasomal proteolysis of N-linked glycoproteins through glycan removal.
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