Charged N-terminus of Influenza Fusion Peptide Facilitates Membrane Fusion

Cleavage of hemagglutinin precursor (HA0) by cellular proteases results in the formation of two subunits, HA1 and HA2. The N-terminal fragment of HA2, named a fusion peptide (HAfp), possess a charged, amine N-terminus. It has been shown that the N-terminus of HAfp stabilizes the structure of a helical hairpin observed for a 23-amino acid long peptide (HAfp1-23), whose larger activity than HAfp1-20 has been demonstrated recently. In this paper, we analyze the effect of N-terminal charge on peptide-mediated fusion efficiency and conformation changes at the membrane interface by comparison with the corresponding N-acetylated peptides of 20- and 23-amino acid lengths. We found that higher fusogenic activities of peptides with unmodified amino termini correlates with their ability to form helical hairpin structures oriented perpendicularly to the membrane plane. Molecular dynamics simulations showed that acetylated peptides adopt open and surface-bound conformation more often, which induced less disorder of the phospholipid chains, as compared to species with unmodified amino termini.