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Cryo-electron microscopy studies of the influenza haemagglutinin glycoprotein at the low pH of host endosomes reveals structural intermediates, offering a dynamic view of how the protein mediates membrane fusion.
Infection by enveloped viruses involves fusion of their lipid envelopes with cellular membranes to release the viral genome into cells. For HIV, Ebola, influenza and numerous other viruses, envelope glycoproteins bind the infecting virion to cell-surface receptors and mediate membrane fusion. In the case of influenza, the receptor-binding glycoprotein is the haemagglutinin (HA), and following receptor-mediated uptake of the bound virus by endocytosis(1), it is the HA that mediates fusion of the virus envelope with the membrane of the endosome(2). Each subunit of the trimeric HA consists of two disulfide-linked polypeptides, HA1 and HA2. The larger, virus-membrane-distal, HA1 mediates receptor binding
