Order and disorder control the functional rearrangement of influenza hemagglutinin.
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ABSTRACT:
SUBMITTER: Lin X
PROVIDER: S-EPMC4143043 | biostudies-literature | 2014 Aug
REPOSITORIES: biostudies-literature
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Project description:Membrane fusion is the critical step for infectious cell penetration by enveloped viruses. We have previously used single-virion measurements of fusion kinetics to study the molecular mechanism of influenza-virus envelope fusion. Published data on fusion inhibition by antibodies to the 'stem' of influenza virus hemagglutinin (HA) now allow us to incorporate into simulations the provision that some HAs are inactive. We find that more than half of the HAs are unproductive even for virions with no bound antibodies, but that the overall mechanism is extremely robust. Determining the fraction of competent HAs allows us to determine their rates of target-membrane engagement. Comparison of simulations with data from H3N2 and H1N1 viruses reveals three independent functional variables of HA-mediated membrane fusion closely linked to neutralization susceptibility. Evidence for compensatory changes in the evolved mechanism sets the stage for studies aiming to define the molecular constraints on HA evolvability.
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Project description:A spin-labeling study of interactions of a fusion peptide from the hemagglutinin of the influenza virus, wt20, and a fusion-inactive mutant DeltaG1 with dimyristoylphosphatidylcholine (DMPC) and 1-palmitoyl-2-oleoyl-phosphatdylcholine bilayers was performed. We found that upon binding of wt20, the ordering of headgroups and the ordering of acyl chains near the headgroup increased significantly, in a manner consistent with a cooperative phenomenon. However, changes in the order at the end of the acyl chains were negligible. The ordering effect of wt20 on the headgroup was much stronger at pH 5 than at pH 7. No effect of DeltaG1 binding on the order of bilayers was evident. We also found that 1-palmitoyl-2-hydroxyl phosphatidylcholine, a membrane-fusion inhibitor, decreased the ordering of DMPC headgroups, whereas arachidonic acid, a membrane-fusion promoter, increased the ordering of DMPC headgroups. These results suggest that increases in headgroup ordering may be important for membrane fusion. We propose that upon binding of wt20, which is known to affect only the outer leaflet of the bilayer, this outer leaflet becomes more ordered, and thus more solid-like. Then the coupling between the hardened outer leaflet and the softer inner leaflet generates bending stresses in the bilayer, which tend to increase the negative curvature of the bilayer. We suggest that the increased ordering in the headgroup region enhances dipolar interactions and lowers electrostatic energy, which may provide an energy source for membrane fusion. Possible roles of bending stresses in promoting membrane fusion are discussed.
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Project description:In June 2013, the first human infection by avian influenza A(H6N1) virus was reported in Taiwan. This incident raised the concern for possible human epidemics and pandemics from H6 viruses. In this study, we performed structural and functional investigation on the hemagglutinin (HA) proteins of the human-infecting A/Taiwan/2/2013(H6N1) (TW H6) virus and an avian A/chicken/Guangdong/S1311/2010(H6N6) (GD H6) virus that transmitted efficiently in guinea pigs. Our results revealed that in the presence of HA1 Q226, the triad of HA1 S137, E190 and G228 in GD H6 HA allows the binding to both avian- and human-like receptors with a slight preference for avian receptors. Its conservation among the majority of H6 HAs provides an explanation for the broader host range of this subtype. Furthermore, the triad of N137, V190 and S228 in TW H6 HA may alleviate the requirement for a hydrophobic residue at HA1 226 of H2 and H3 HAs when binding to human-like receptors. Consequently, TW H6 HA has a slight preference for human receptors, thus may represent an intermediate towards a complete human adaptation. Importantly, the triad observed in TW H6 HA is detected in 74% H6 viruses isolated from Taiwan in the past 14 years, suggesting an elevated threat of H6 viruses from this region to human health. The novel roles of the triad at HA1 137, 190 and 228 of H6 HA in binding to receptors revealed here may also be used by other HA subtypes to achieve human adaptation, which needs to be further tested in laboratory and closely monitored in field surveillance.
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Project description:Influenza virus hemagglutinin (HA), a homotrimeric integral membrane glycoprotein essential for viral infection, is engaged in two biological functions: recognition of target cells' receptor proteins and fusion of viral and endosomal membranes, both requiring substantial conformational flexibility from the part of the glycoprotein. The different modes of collective motions underlying the functional mobility/adaptability of the protein are determined in the present study using an extension of the Gaussian network model (GNM) to treat concerted anisotropic motions. We determine the molecular mechanisms that may underlie HA function, along with the structural regions or residues whose mutations are expected to impede function. Good agreement between theoretically predicted fluctuations of individual residues and corresponding x-ray crystallographic temperature factors is found, which lends support to the GNM elucidation of the conformational dynamics of HA by focusing upon a subset of dominant modes. The lowest frequency mode indicates a global torsion of the HA trimer about its longitudinal axis, accompanied by a substantial mobility at the viral membrane connection. This mode is proposed to constitute the dominant molecular mechanism for the translocation and aggregation of HAs, and for the opening and dilation of the fusion pore. The second and third collective modes indicate a global bending, allowing for a large lateral surface exposure, which is likely to facilitate the close association of the viral and endosomal membranes before pore opening. The analysis of kinetically hot residues, in contrast, reveals a localization of energy centered around the HA2 residue Asp112, which apparently triggers the solvent exposure of the fusion peptide.
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