Shallow boomerang-shaped influenza hemagglutinin G13A mutant structure promotes leaky membrane fusion.
Our previous studies showed that an angled boomerang-shaped structure of the influenza hemagglutinin (HA) fusion domain is critical for virus entry into host cells by membrane fusion. Because the acute angle of ∼105° of the wild-type fusion domain promotes efficient non-leaky membrane fusion, we asked whether different angles would still support fusion and thus facilitate virus entry. Here, we show that the G13A fusion domain mutant produces a new leaky fusion phenotype. The mutant fusion domain structure was solved by NMR spectroscopy in a lipid environment at fusion pH. The mutant adopted a boomerang structure similar to that of wild type but with a shallower kink angle of ∼150°. G13A perturbed the structure of model membranes to a lesser degree than wild type but to a greater degree than non-fusogenic fusion domain mutants. The strength of G13A binding to lipid bilayers was also intermediate between that of wild type and non-fusogenic mutants. These membrane interactions provide a clear link between structure and function of influenza fusion domains: an acute angle is required to promote clean non-leaky fusion suitable for virus entry presumably by interaction of the fusion domain with the transmembrane domain deep in the lipid bilayer. A shallower angle perturbs the bilayer of the target membrane so that it becomes leaky and unable to form a clean fusion pore. Mutants with no fixed boomerang angle interacted with bilayers weakly and did not promote any fusion or membrane perturbation.
Lai
Alex L
AL
Center for Membrane Biology, Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia 22903-0886, USA.
Tamm
Lukas K
LK
D000818:Animals; D002460:Cell Line; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D007251:Influenza, Human / Q000503:physiopathology* / Q000821:virology; D008561:Membrane Fusion; D008968:Molecular Conformation; D020125:Mutation, Missense; D009975:Orthomyxoviridae / Q000235:genetics / Q000502:physiology*; D017434:Protein Structure, Tertiary; D053586:Virus Internalization
D019267:Hemagglutinin Glycoproteins, Influenza Virus
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