Structural Characterizations of Fusion Peptide Analogs of Influenza Virus Hemagglutinin

ABSTRACT Influenza virus hemagglutinin undergoes a conformational change in which a loop-to-helix “spring-loaded” conformational change forms a coiled coil that positions the fusion peptide for interaction with the target bilayer. Previous work has shown that two proline mutations designed to disrupt this change disrupt fusion but did not determine the basis for the fusion defect. In this work, we made six additional mutants with single proline substitutions in the region that undergoes the spring-loaded conformational change and two additional mutants with double proline substitutions in this region. All double mutants were fusion inactive. We analyzed one double mutant, F63P/F70P, as an example. We observed that F63P/F70P undergoes key low-pH-induced conformational changes and binds tightly to target membranes. However, limited proteolysis and electron microscopy observations showed that the mutant forms a coiled coil that is only ∼50% the length of the wild type, suggesting that it is splayed in its N-terminal half. This work further supports the hypothesis that the spring-loaded conformational change is necessary for fusion. Our data also indicate that the spring-loaded conformational change has another role beyond presenting the fusion peptide to the target membrane.

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Bilayer Conformation of Fusion Peptide of Influenza Virus Hemagglutinin: A Molecular Dynamics Simulation Study

Biophysical Journal ◽

10.1529/biophysj.103.024562 ◽

2004 ◽

Vol 87 (1) ◽

pp. 14-22 ◽

Cited By ~ 36

Author(s):

Qiang Huang ◽

Cheng-Lung Chen ◽

Andreas Herrmann

Keyword(s):

Molecular Dynamics ◽

Influenza Virus ◽

Molecular Dynamics Simulation ◽

Simulation Study ◽

Fusion Peptide ◽

Dynamics Simulation ◽

Influenza Virus Hemagglutinin

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H+-induced Membrane Insertion of Influenza Virus Hemagglutinin Involves the HA2 Amino-terminal Fusion Peptide but Not the Coiled Coil Region

Journal of Biological Chemistry ◽

10.1074/jbc.271.23.13417 ◽

1996 ◽

Vol 271 (23) ◽

pp. 13417-13421 ◽

Cited By ~ 149

Author(s):

Peter Durrer ◽

Carmela Galli ◽

Stefan Hoenke ◽

Chantal Corti ◽

Reinhard Glück ◽

...

Keyword(s):

Influenza Virus ◽

Coiled Coil ◽

Fusion Peptide ◽

Membrane Insertion ◽

Induced Membrane ◽

Amino Terminal ◽

Influenza Virus Hemagglutinin ◽

Coiled Coil Region

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Intermonomer Interactions in Hemagglutinin Subunits HA1 and HA2 Affecting Hemagglutinin Stability and Influenza Virus Infectivity

Journal of Virology ◽

10.1128/jvi.00939-15 ◽

2015 ◽

Vol 89 (20) ◽

pp. 10602-10611 ◽

Cited By ~ 14

Author(s):

Wei Wang ◽

Christopher J. DeFeo ◽

Esmeralda Alvarado-Facundo ◽

Russell Vassell ◽

Carol D. Weiss

Keyword(s):

Influenza Virus ◽

Influenza A Virus ◽

Influenza A ◽

Seasonal Influenza ◽

Virus Entry ◽

H1n1 Influenza ◽

Fusion Peptide ◽

Virus Infectivity ◽

Influenza Virus Hemagglutinin ◽

2009 H1n1

ABSTRACTInfluenza virus hemagglutinin (HA) mediates virus entry by binding to cell surface receptors and fusing the viral and endosomal membranes following uptake by endocytosis. The acidic environment of endosomes triggers a large-scale conformational change in the transmembrane subunit of HA (HA2) involving a loop (B loop)-to-helix transition, which releases the fusion peptide at the HA2 N terminus from an interior pocket within the HA trimer. Subsequent insertion of the fusion peptide into the endosomal membrane initiates fusion. The acid stability of HA is influenced by residues in the fusion peptide, fusion peptide pocket, coiled-coil regions of HA2, and interactions between the surface (HA1) and HA2 subunits, but details are not fully understood and vary among strains. Current evidence suggests that the HA from the circulating pandemic 2009 H1N1 influenza A virus [A(H1N1)pdm09] is less stable than the HAs from other seasonal influenza virus strains. Here we show that residue 205 in HA1 and residue 399 in the B loop of HA2 (residue 72, HA2 numbering) in different monomers of the trimeric A(H1N1)pdm09 HA are involved in functionally important intermolecular interactions and that a conserved histidine in this pair helps regulate HA stability. An arginine-lysine pair at this location destabilizes HA at acidic pH and mediates fusion at a higher pH, while a glutamate-lysine pair enhances HA stability and requires a lower pH to induce fusion. Our findings identify key residues in HA1 and HA2 that interact to help regulate H1N1 HA stability and virus infectivity.IMPORTANCEInfluenza virus hemagglutinin (HA) is the principal antigen in inactivated influenza vaccines and the target of protective antibodies. However, the influenza A virus HA is highly variable, necessitating frequent vaccine changes to match circulating strains. Sequence changes in HA affect not only antigenicity but also HA stability, which has important implications for vaccine production, as well as viral adaptation to hosts. HA from the pandemic 2009 H1N1 influenza A virus is less stable than other recent seasonal influenza virus HAs, but the molecular interactions that contribute to HA stability are not fully understood. Here we identify molecular interactions between specific residues in the surface and transmembrane subunits of HA that help regulate the HA conformational changes needed for HA stability and virus entry. These findings contribute to our understanding of the molecular mechanisms controlling HA function and antigen stability.

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Membrane Structures of the Hemifusion-Inducing Fusion Peptide Mutant G1S and theFusion-Blocking Mutant G1V of Influenza Virus HemagglutininSuggest a Mechanism for Pore Opening in MembraneFusion

Journal of Virology ◽

10.1128/jvi.79.18.12065-12076.2005 ◽

2005 ◽

Vol 79 (18) ◽

pp. 12065-12076 ◽

Cited By ~ 51

Author(s):

Yinling Li ◽

Xing Han ◽

Alex L. Lai ◽

John H. Bushweller ◽

David S. Cafiso ◽

...

Keyword(s):

Influenza Virus ◽

Membrane Fusion ◽

Lipid Bilayer ◽

Membrane Surface ◽

Helical Structure ◽

Fusion Peptide ◽

Membrane Structures ◽

Influenza Virus Hemagglutinin ◽

Target Membrane ◽

Pore Opening

ABSTRACT Influenza virus hemagglutinin (HA)-mediated membrane fusion is initiated by a conformational change that releases a V-shaped hydrophobic fusion domain, the fusion peptide, into the lipid bilayer of the target membrane. The most N-terminal residue of this domain, a glycine, is highly conserved and is particularly critical for HA function; G1S and G1V mutant HAs cause hemifusion and abolish fusion, respectively. We have determined the atomic resolution structures of the G1S and G1V mutant fusion domains in membrane environments. G1S forms a V with a disrupted “glycine edge” on its N-terminal arm and G1V adopts a slightly tilted linear helical structure in membranes. Abolishment of the kink in G1V results in reduced hydrophobic penetration of the lipid bilayer and an increased propensity to formβ -structures at the membrane surface. These results underline the functional importance of the kink in the fusion peptide and suggest a structural role for the N-terminal glycine ridge in viral membrane fusion.

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