Effect of inhibitors of glycosylation on proteolytic activation of avian influenza virus hemagglutinins: discrimination between tryptic cleavage and elimination of the connecting peptide.

The glycosylation inhibitors tunicamycin (TM), 2-deoxyglucose (2-dg), bromoconduritol (BC; 3,5/4,6-6-bromo 3,4,5-trihydroxycyclohex-1-ene), and N-methyl-deoxynojirimycin (MdN) have been used to study the role of glycosylation in the two proteolytic reactions involved in the biological activation of H7 influenza virus hemagglutinins (HAs): trypsinlike cleavage and subsequent elimination of the connecting peptide. The results obtained revealed that trypsin-like cleavage of the HAs of pathogenic strains does not require glycosylation, since these HAs were efficiently cleaved in the presence of TM and 2-dg. The elimination of the connecting peptide between HA1 and HA2, however, appears to require the transfer of oligosaccharides onto the HA polypeptide, since this activity was blocked by TM and by 2-dg. Elimination was not blocked by BC or MdN, which inhibit glucose trimming and subsequent conversion of the high-mannose type to the complex type of carbohydrate.