Membrane fusion of enveloped viruses with cellular membranes is mediated by viral glycoproteins, which are activated by proteolytic cleavage and/or interaction with cellular receptors. Fusion entails extensive conformational changes of the fusion protein that initially anchors to cellular membranes thus bridging two bilayers. Further refolding into a hairpin-like structure pulls viral and cellular membranes into close proximity to permit lipid bilayer fusion. Refolding provides the energy for fusion, which follows several defined lipidic intermediate states occurring concomitantly with refolding. Although different classes of fusion proteins use different structural motifs, the principle of repositioning both membrane anchors, the transmembrane and the fusion peptide region, at the same end of an elongated hairpin structure generated by receptor binding is maintained in all known viral fusion protein structures, suggesting that they follow similar principles to achieve lipid bilayer fusion.
Membrane Fusion