Читать книгу Principles of Virology - Jane Flint, S. Jane Flint - Страница 237

The envelope proteins of alphaviruses (E1) and flaviviruses (E) exemplify class II viral fusion proteins. In contrast to type I fusion proteins, E1 and E proteins do not form coiled coils. The proteins share a common fold with a central β-sandwich domain I flanked by domains II and III that tile the surface of the virus particles as dimers (Fig. 5.18A). A helical membrane-proximal domain links this structure to a transmembrane domain that spans the membrane twice. At low pH, the fusion proteins undergo conformational changes that extend domain II toward the endosome membrane, allowing insertion of the fusion loop in the target membrane (Fig. 5.18). During this transition, the dimers dissociate and reassemble into trimers. Refolding of domain III and the membrane-proximal region helix around the central β-sandwich brings the viral membrane close to the target membrane, adopting a hairpin structure as do class I fusion proteins (Fig. 5.13). This same structure is adopted by a eukaryotic protein and supports its function as a fusion protein during sexual reproduction (Box. 5.4).