ABSTRACT
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Membrane fusion is an essential process in intracellular transport, cellular secretion, and fertilization. All enveloped animal viruses must accomplish membrane fusion with target cells as a precursor to infection. Understanding the general characteristics of protein-mediated membrane fusion is the first step toward developing general strategies to control this ubiquitous biological event. At present, most of the membrane glycoproteins that mediate membrane fusion and entry of the known pathogenic enveloped animal viruses have been identified. Here, we focus primarily on the membrane fusion glycoprotein hemagglutinin (HA) of influenza virus. Its ectodomain, which requires low pH to initiate fusion, was the first membrane fusion protein whose crystal structure was solved (Wilson et al., 1981), and it remains the prototypical fusion protein (Skehel and Wiley, 1998; Sutton et al., 1998; Baker et al., 1999; Bentz, 2000b; Bentz and Mittal, 2003).
