1.G.5 The Viral Pore-forming Membrane Fusion Protein-5 (VMFP5) Family
The Vesicular Stomatitis Virus (VSV) G protein and the HSV-1gB fusion protein are of Class III. They do not require proteolytic processing for function and consist of both α- and β-structure. The native trimers remain trimers upon membrane insertion to promote pore formation and fusion (White et al. 2008). The fusogenic transition entails an extensive structural reorganization of G (Roche et al., 2007). In the prefusion form, G has the shape of a tripod with the fusion loops exposed, which point toward the viral membrane with the antigenic sites located at the distal end of the molecule. A large number of G glycoproteins, perhaps organized as in the crystals, act cooperatively to induce membrane merging. Fusion occurs in the endosome in response to the acidic pH. The transmembrane domain in the G protein may induce positive intrinsic curvature and thereby induce formation of fusion pores (Sengupta et al. 2014).