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X-31 Hemagglutinin Precursor HA0 at pH 7.5 after reneutralizationX-31 Hemagglutinin Precursor HA0 at pH 7.5 after reneutralization
Structural highlights
FunctionWAC_BPT4 Chaperone responsible for attachment of long tail fibers to virus particle. Forms the fibrous structure on the neck of the virion called whiskers. During phage assembly, 6 fibritin molecules attach to each virion neck through their N-terminal domains, to form a collar with six fibers ('whiskers').HEMA_I68A0 Binds to sialic acid-containing receptors on the cell surface, bringing about the attachment of the virus particle to the cell. This attachment induces virion internalization of about two third of the virus particles through clathrin-dependent endocytosis and about one third through a clathrin- and caveolin-independent pathway. Plays a major role in the determination of host range restriction and virulence. Class I viral fusion protein. Responsible for penetration of the virus into the cell cytoplasm by mediating the fusion of the membrane of the endocytosed virus particle with the endosomal membrane. Low pH in endosomes induces an irreversible conformational change in HA2, releasing the fusion hydrophobic peptide. Several trimers are required to form a competent fusion pore. Publication Abstract from PubMedThe subunits of the influenza hemagglutinin (HA) trimer are synthesized as single-chain precursors (HA0s) that are proteolytically cleaved into the disulfide-linked polypeptides HA1 and HA2. Cleavage is required for activation of membrane fusion at low pH, which occurs at the beginning of infection following transfer of cell-surface-bound viruses into endosomes. Activation results in extensive changes in the conformation of cleaved HA. To establish the overall contribution of cleavage to the mechanism of HA-mediated membrane fusion, we used cryogenic electron microscopy (cryo-EM) to directly image HA0 at neutral and low pH. We found extensive pH-induced structural changes, some of which were similar to those described for intermediates in the refolding of cleaved HA at low pH. They involve a partial extension of the long central coiled coil formed by melting of the preexisting secondary structure, threading it between the membrane-distal domains, and subsequent refolding as extended helices. The fusion peptide, covalently linked at its N terminus, adopts an amphipathic helical conformation over part of its length and is repositioned and packed against a complementary surface groove of conserved residues. Furthermore, and in contrast to cleaved HA, the changes in HA0 structure at low pH are reversible on reincubation at neutral pH. We discuss the implications of covalently restricted HA0 refolding for the cleaved HA conformational changes that mediate membrane fusion and for the action of antiviral drug candidates and cross-reactive anti-HA antibodies that can block influenza infectivity. Reversible structural changes in the influenza hemagglutinin precursor at membrane fusion pH.,Garcia-Moro E, Zhang J, Calder LJ, Brown NR, Gamblin SJ, Skehel JJ, Rosenthal PB Proc Natl Acad Sci U S A. 2022 Aug 16;119(33):e2208011119. doi: , 10.1073/pnas.2208011119. Epub 2022 Aug 8. PMID:35939703[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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