N-Glycosylation during translation is essential for human arylacetamide deacetylase enzyme activity

Abstract

Human arylacetamide deacetylase (AADAC) can hydrolyze clinical drugs such as flutamide, phenacetin, and rifamycins. AADAC is a glycoprotein, but the role of glycosylation remains unclear. In the present study, we investigated the effect of glycosylation on AADAC enzyme activity. Immunoblot analysis of mutant AADACs that contained an asparagine (N, Asn) to glutamine (Q, Gln) substitution at either residue 78 or 282 (N78Q or N282Q) showed a different migration compared with the wild-type protein. A mutant AADAC that contained N to Q substitutions at both residue 78 and 282 (N78Q/N282Q) showed a similar migration to AADAC in human liver microsomes (HLM) treated with endoglycosidase H (Endo H), which produces deglycosylated proteins. This result indicated that AADAC was glycosylated at both N78 and N282. Mutant types of AADAC with the N282Q and the N78Q/N282Q substitutions showed dramatically lower phenacetin hydrolase activity than did the wild-type protein. The treatment of wild-type AADAC-expressing HuH-7 cells with tunicamycin, which produces unglycosylated protein, decreased AADAC enzyme activity. However, the treatment of the HLM with Endo H caused no decrease of AADAC activity. Thus, the oligosaccharide chain, per se, was not important for AADAC activity in the mature form. The mutant types of AADAC containing the N282Q and the N78Q/N282Q substitutions were not detected by immunoblotting analysis after non-reducing SDS-PAGE, suggesting that the glycosylation of AADAC at N282 was important for proper protein folding. Overall, this study found that the translational, but not post-translational, N-glycosylation of AADAC plays a crucial role in regulating AADAC enzyme activity.