Transmembrane domains of H1 and H3 hemagglutinin contribute to membrane fusion in a different manner

Hemagglutinin (HA), a fusion protein of influenza virus, has been extensively researched as a model fusion viral protein. However, most of the efforts focus on the fusion peptide (FP) and the ectodomain, while relatively little is known about the "membrane anchor", a transmembrane domain (TMD). While the structural insights on H1 subtype full-length HA underlay the influence of TMD on the ectodomain orientations, the structures representing the other phylogenetic group are still unavailable. Inspired by the sequential varieties of TMDs in both groups, we performed a series of experiments on full-length HA proteins with H1and H3-swapped TMD domains in virus-like particles (VLP). In parallel, we studied the behaviour an and interplay of FP and TMD-corresponding fragments with the use of artificial membrane systems and molecular dynamics simulations. We detect clearly a distinct interplay between FP and TMDs in the two phylogenetic groups. We observe that TMD-dependent fusion activity originates from TMD-lipid interactions, but not direct FP:TMD complexing.