Structure-function relationship of the influenza fusion peptide

Abstract

Influenza is an enveloped virus which enters the host cell through en-docytosis-mediated mechanism. To enable the release genetic material, a process of fusion between viral and host cell membranes occurs, which is mediated by influenza hemagglutinin (HA) protein. The N-terminal fragment of hemagglutinin HA2 subunit, directly interacting with the membrane, is named a fusion peptide (HAfp), since it is able to promote fusion also as a synthetic fragment. Its C-terminal part contains three residues (W21-Y22-G23), which are highly conserved among various serotypes of Influenza A. It has been shown that the peptide length has an influence on its structure: HAfp1-20 forms a boomerangin contrast to a tight helical hairpin formed by HAfp1-23. To gain more insight into the role of the conserved residues, we studied the effect of peptide length on fusion properties, its structural dynamics, and par-titioning to the phospholipid bilayer. By means of molecular dynamics simulations and spectroscopic measurements, we showed that the presence of three C-terminal residues in HAfp1-23 promotes the for-mation of hairpin structure. In contrast to less structured HAfp1-20,it orients perpendicularly to the membrane plane and induces more disorder in the surrounding lipids. Using a novel fusion visualization assay based on FLIM microscopy on giant unilamellar vesicles (GUV), we observed that HAfp1-23 promotes fusion to a higher extent than HAfp1-20. Moreover, we report cholesterolenriched domain formation exclusively by the longer fusion peptide. This redistribution of membrane components in fluid phases is likely to play a role during membrane fusion.