tetano
Editor, Senior Moderator
J Virol. 2012 Jan 18. [Epub ahead of print]
Structural changes in influenza virus at low pH characterized by cryo-electron tomography.
Fontana J, Cardone G, Heymann JB, Winkler DC, Steven AC.
Source
Laboratory of Structural Biology, National Institute of Arthritis, Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, Maryland 20892, U.S.A.
Abstract
Influenza virus enters host cells by endocytosis. The low pH of endosomes triggers conformational changes in hemagglutinin (HA) that mediate fusion of the viral and endosomal membranes. We have used cryo-electron tomography to visualize influenza A virus at pH 4.9, a condition known to induce fusogenicity. After 30 min, when all virions are in the post-fusion state, dramatic changes in morphology are apparent: elongated particles are no longer observed; larger particles representing fused virions appear; the HA spikes become conspicuously disorganized; a layer of M1 matrix protein is no longer resolved on most virions; and the ribonucleoprotein complexes (RNPs) coagulate on the interior surface of the virion. To probe for intermediate states, preparations were imaged after 5 min at pH 4.9. These virions could be classified according to their glycoprotein arrays (organized or disorganized) and whether or not they have a resolved M1 layer. Employing subtomogram averaging, we found, in addition to the neutral-pH state of HA, two intermediate conformations that appear respectively to reflect an outwards movement of the fusion peptide and rearrangement of the HA1 subunits. These changes are reversible. The tomograms also document pH-induced changes affecting the M1 layer that appear to render the envelope more pliable and hence conducive to fusion. However, it appears desirable for productive infection that fusion should proceed before the RNPs become coagulated with matrix protein, as eventually happens at low pH.
PMID:
22258245
[PubMed - as supplied by publisher]
http://www.ncbi.nlm.nih.gov/pubmed/22258245
Structural changes in influenza virus at low pH characterized by cryo-electron tomography.
Fontana J, Cardone G, Heymann JB, Winkler DC, Steven AC.
Source
Laboratory of Structural Biology, National Institute of Arthritis, Musculoskeletal and Skin Diseases, National Institutes of Health, Bethesda, Maryland 20892, U.S.A.
Abstract
Influenza virus enters host cells by endocytosis. The low pH of endosomes triggers conformational changes in hemagglutinin (HA) that mediate fusion of the viral and endosomal membranes. We have used cryo-electron tomography to visualize influenza A virus at pH 4.9, a condition known to induce fusogenicity. After 30 min, when all virions are in the post-fusion state, dramatic changes in morphology are apparent: elongated particles are no longer observed; larger particles representing fused virions appear; the HA spikes become conspicuously disorganized; a layer of M1 matrix protein is no longer resolved on most virions; and the ribonucleoprotein complexes (RNPs) coagulate on the interior surface of the virion. To probe for intermediate states, preparations were imaged after 5 min at pH 4.9. These virions could be classified according to their glycoprotein arrays (organized or disorganized) and whether or not they have a resolved M1 layer. Employing subtomogram averaging, we found, in addition to the neutral-pH state of HA, two intermediate conformations that appear respectively to reflect an outwards movement of the fusion peptide and rearrangement of the HA1 subunits. These changes are reversible. The tomograms also document pH-induced changes affecting the M1 layer that appear to render the envelope more pliable and hence conducive to fusion. However, it appears desirable for productive infection that fusion should proceed before the RNPs become coagulated with matrix protein, as eventually happens at low pH.
PMID:
22258245
[PubMed - as supplied by publisher]
http://www.ncbi.nlm.nih.gov/pubmed/22258245