Significance of viral glycoproteins for infectivity and pathogenicity.

Disease resulting from virus infection is a complex event depending on the close interaction of viral and cellular factors. Through the application of biochemical and genetic methods, it is now possible to gain an insight into the molecular basis of these interactions. Thus, it has been shown that the glycoproteins of enveloped viruses play a central role in the initiation of infection. They are responsible not only for the adsorption of virions to cellular receptors, but are also for the entry of the genome into the cell by the fusion of viral envelopes with cellular membranes. Evidence is growing that the fusogenic glycoproteins are frequently activated by cellular proteases. The structure of the proteins at the cleavage site and the availability of a suitable protease are critical for tissue tropism, spread of the virus in the infected organism and, thus, for pathogenicity. This will be demonstrated here by the example of the haemagglutinin of influenza viruses.