title: Shallow boomerang-shaped influenza hemagglutinin G13A mutant structure promotes leaky membrane fusion.
abstract: 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.
authors.affiliation: Center for Membrane Biology, Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia 22903-0886, USA.
authors.forename: Alex L
authors.initials: AL
authors.lastname: Lai
authors.forename: Lukas K
authors.initials: LK
authors.lastname: Tamm
mesh_terms: 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
chemical_list: D019267:Hemagglutinin Glycoproteins, Influenza Virus
references.citation: J Biomol NMR. 1996 Sep;8(2):136-46
references.pmid: 8914272
references.citation: Biochim Biophys Acta. 2007 Dec;1768(12):3052-60
references.pmid: 17963720
references.citation: J Mol Biol. 1997 Oct 17;273(1):283-98
references.pmid: 9367762
references.citation: Nat Struct Biol. 2001 Aug;8(8):715-20
references.pmid: 11473264
references.citation: J Biol Chem. 2006 Mar 3;281(9):5760-70
references.pmid: 16407195
references.citation: Crit Rev Biochem Mol Biol. 2008 May-Jun;43(3):189-219
references.pmid: 18568847
references.citation: Retrovirology. 2008 Dec 10;5:111
references.pmid: 19077194
references.citation: Q Rev Biophys. 1997 Nov;30(4):365-429
references.pmid: 9634652
references.citation: J Cell Biol. 2000 Oct 16;151(2):425-37
references.pmid: 11038188
references.citation: Biophys J. 2007 Aug 1;93(3):876-85
references.pmid: 17513369
references.citation: Biochim Biophys Acta. 1997 Nov 13;1330(1):17-28
references.pmid: 9375809
references.citation: J Biol Chem. 2007 Aug 17;282(33):23946-56
references.pmid: 17567572
references.citation: J Biomol NMR. 1999 Mar;13(3):289-302
references.pmid: 10212987
references.citation: Biochemistry. 1996 Apr 16;35(15):4956-65
references.pmid: 8664288
references.citation: Biophys J. 2003 Sep;85(3):1725-33
references.pmid: 12944287
references.citation: Biochim Biophys Acta. 2003 Jul 11;1614(1):14-23
references.pmid: 12873762
references.citation: J Biol Chem. 2000 Mar 3;275(9):6160-6
references.pmid: 10692407
references.citation: Biochemistry. 2003 Jun 17;42(23):7245-51
references.pmid: 12795621
references.citation: J Biomol NMR. 1995 Nov;6(3):277-93
references.pmid: 8520220
references.citation: Proc Natl Acad Sci U S A. 2000 Nov 21;97(24):13097-102
references.pmid: 11069282
references.citation: Cell. 1993 May 21;73(4):823-32
references.pmid: 8500173
references.citation: J Mol Biol. 2000 Dec 15;304(5):953-65
references.pmid: 11124039
references.citation: J Virol. 2005 Sep;79(18):12065-76
references.pmid: 16140782
references.citation: J Mol Biol. 1984 Dec 15;180(3):741-51
references.pmid: 6084720
references.citation: Mol Biol Cell. 1999 Aug;10(8):2759-69
references.pmid: 10436026
references.citation: Nat Struct Mol Biol. 2008 Jul;15(7):690-8
references.pmid: 18596815
references.citation: Biophys J. 1996 May;70(5):2275-86
references.pmid: 9172751
references.citation: J Biomol NMR. 1996 Dec;8(4):477-86
references.pmid: 9008363