Structural characterization of viral fusion proteins.

Infection by enveloped viruses is initiated by the fusion of viral and cellular membranes. In many cases, the viral membrane proteins that mediate fusion must undergo conformational changes to become active. Influenza hemagglutinin, for example, is activated by a dramatic conformational rearrangement, triggered by the low pH of the intracellular compartment in which fusion occurs. Structural characterization of this rearrangement has led to a reconsideration of how hemagglutinin mediates membrane fusion.