The Influenza Hemagglutinin Fusion Domain Is an Amphipathic Helical Hairpin That Functions by Inducing Membrane Curvature

• Published in: The Journal of biological chemistry 2015-01, Vol.290 (1), p.228-238
• Main Authors: Smrt, Sean T., Draney, Adrian W., Lorieau, Justin L.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Binding Sites; Dimyristoylphosphatidylcholine - chemistry; Escherichia coli - genetics; Escherichia coli - metabolism; Fusion Peptide; Gene Expression; Hemagglutinin Glycoproteins, Influenza Virus - chemistry; Hemagglutinin Glycoproteins, Influenza Virus - genetics; Hemagglutinin Glycoproteins, Influenza Virus - metabolism; Hydrophobic and Hydrophilic Interactions; Influenza; Influenza A virus - chemistry; Lipid Bilayers - chemistry; Membrane Fusion; Membrane Protein; Micelles; Models, Molecular; Molecular Biophysics; Molecular Sequence Data; Nuclear Magnetic Resonance (NMR); Phospholipid Ethers - chemistry; Protein Binding; Protein Structure, Secondary; Protein Structure, Tertiary; Recombinant Fusion Proteins - chemistry; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Static Electricity; Structural Biology; Thermodynamics
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M114.611657

The highly conserved N-terminal 23 residues of the hemagglutinin glycoprotein, known as the fusion peptide domain (HAfp23), is vital to the membrane fusion and infection mechanism of the influenza virus. HAfp23 has a helical hairpin structure consisting of two tightly packed amphiphilic helices that rest on the membrane surface. We demonstrate that HAfp23 is a new class of amphipathic helix that functions by leveraging the negative curvature induced by two tightly packed helices on membranes. The helical hairpin structure has an inverted wedge shape characteristic of negative curvature lipids, with a bulky hydrophobic region and a relatively small hydrophilic head region. The F3G mutation reduces this inverted wedge shape by reducing the volume of its hydrophobic base. We show that despite maintaining identical backbone structures and dynamics as the wild type HAfp23, the F3G mutant has an attenuated fusion activity that is correlated to its reduced ability to induce negative membrane curvature. The inverted wedge shape of HAfp23 is likely to play a crucial role in the initial stages of membrane fusion by stabilizing negative curvature in the fusion stalk.The influenza hemagglutinin fusion peptide is responsible for fusion of viral and endosomal membranes upon infection. Negatively induced curvature and fusion activity were significantly reduced by changing the shape of the fusion peptide. The hemagglutinin fusion peptide structure promotes negative membrane curvature. This work enables elucidates how a crucial component of influenza infection functions and can be targeted.