Simulations and Experiments Show a Mechanistic Role for Influenza Fusion Peptides in Membrane Bending and Fusion Stoichiometry

Abstract

Membrane fusion by influenza virus is exquisitely sensitive to the N-terminal residues of the membrane-inserted fusion peptide. Just how single-residue substitutions at the N-terminus of this peptide can cause large changes in fusion phenotype and viral infectivity has remained a puzzle in the field. Here, we use a combination of atomic-resolution simulations of viral membrane fusion and fluorescence microscopy to probe the role of the fusion peptide N-terminus in controlling fusion behavior. Surprisingly, we find that the formation of highly curved fusion intermediates is highly sensitive to the N-terminus in simulations, and the fusion behavior of both mutant virus and hemagglutinin-expressing cells also suggests a difference in protein stoichiometry required for fusion between wild-type and mutant fusion peptides. Together, these data suggest mechanistic roles for the fusion peptide N-terminus that can be directly connected to fusion behavior and infectious outcomes, helping explain how these seemingly subtle changes to a membrane-inserted peptide can alter the behavior of the entire viral fusion machinery.