Viral glycoprotein heterogeneity-enhancement of functional diversity.

Variations in the amino acid sequence of RNA virus envelope glycoproteins can cause changes in their antigenicity and can alter the host-cell tropism of the virus and the degree of virulence which it exhibits. Such changes may alter the course and outcome of viral diseases, either directly because of changes in the biological properties of the glycoproteins or indirectly through effects on immune surveillance and vaccine efficacy. The nature and extent of glycosylation of the surface glycoproteins of RNA viruses have also been implicated in such phenotypic alterations. It follows therefore that the 'plasticity' of the viral genome and the host-encoded glycosylation machinery combine to create populations of highly diverse viruses. This diversity is considered to be responsible for survival of these viruses in a variety of biological niches and for their ability to overcome the inhibitory effects of neutralizing antibodies and antiviral agents. In this article we discuss the implications of the inter-relationship between these two mechanisms for the generation of diversity.