Definition: In this task, you're given a paragraph from the research paper and your task is to generate a suitable title for the research paper based on the given paper. Under 100 words is a good title length.
Input: Infection by viruses having lipid-bilayer envelopes proceeds through fusion of the viral membrane with a membrane of the target cell. Viral 'fusion proteins' facilitate this process. They vary greatly in structure, but all seem to have a common mechanism of action, in which a ligand-triggered, large-scale conformational change in the fusion protein is coupled to apposition and merger of the two bilayers. We describe three examples-the influenza virus hemagglutinin, the flavivirus E protein and the vesicular stomatitis virus G protein-in some detail, to illustrate the ways in which different structures have evolved to implement this common mechanism. Fusion inhibitors can be effective antiviral agents. 'Enveloped' viruses-those with lipid bilayers as integral parts of their structure-enter the cells they infect by fusion of viral and host-cell membranes. One or more viral membrane proteins facilitate the various fusion steps. Several such fusion proteins have now been studied in great detail, with crystal structures determined for both the form of the protein present on the viral surface before interaction with the cell ('pre-fusion' conformation) and the form of the protein after fusion is complete ('post-fusion' conformation). The proteins show a variety of molecular architectures, but what we can infer from the various structures and from experiments both in solution and with cells suggests that all of them catalyze fusion in essentially the same way. We can even draw a rough analogy to serine proteases, which can have very different polypeptide chain folds but identical active-site mechanisms.

Viral membrane fusion