Glycosylation influencing on fusion activity of HA and HEF structures of influenza viruses

Abstract

Since the most ancient times, influenza viruses have caused lethal respiratory diseases. Their replication process occurs at the epithelial cells of the respiratory tract, where the surface-anchored glycoproteins hemagglutinin (HA) and hemagglutinin-esterase-fusion protein (HEF) of influenza A and C viruses respectively are responsible for the fusion process. The adsorption, sialidase and esterase activities developed by these same structures are inborn, while the fusion process is dependent of previous glycosylation and protein cleavage. Indeed, the glycosylation is strictly related to antigenicity and stability of fusion proteins. This work was designed to analyse the influence of the de-glycosylation for the development of fusion activity, using influenza A and C viruses as study models. The de-glycosylation provoked significative reduction in the fusogenic activity, inducing a reduction equal to 51.0%, 87.5%, 95.5% and 79.3% for A/Memphis/102/72, A/FM/1/47, C/Taylor/1233/47 and C/Paris/1/67 respectively. However, this activity was improved at certain pH values, 10.1% (pH 5.8), 59.4% (pH 5.8), 32.5% (pH 5.8) and 80.7% (pH 5.4) for the 95.7% at pH 5.2 for A/Memphis/102/72, A/FM/1/47, C/Taylor/1233/47 and C/Paris/1/67 of influenza viruses respectively. The fusogenic activity of certain samples was also improved at some pH values. These results permit to conclude that the level of glycosylation is closely related to the protein stability and the de-glycosylation process causes a significative influence on the fusion biological activity.