Hemagglutinin protein, H3 subtype (HA (H3))

The Hemagglutinin protein, H3 subtype (HA H3) is a homotrimeric glycoprotein on the surface of influenza A viruses, specifically the H3N2 strain like A/Aichi/2/1968, functioning as both a receptor-binding and membrane fusion protein essential for viral entry into host cells. It binds sialic acid receptors on respiratory epithelial cells via its HA1 subdomain, facilitating viral attachment, and undergoes pH-dependent conformational changes in endosomes to expose a fusion peptide in the HA2 subdomain, driving fusion of viral and host membranes to release viral RNA. Structurally, HA H3 features a membrane-distal receptor-binding site, vestigial esterase subdomain, fusion subdomain with alpha-helical coiled-coil, and membrane anchor, organized into HA1 and HA2 after proteolytic cleavage of precursor HA0. As part of 16 HA subtypes grouped phylogenetically, H3 belongs to Group 2 clade, with subtype-specific receptor preferences like alpha-2,6-linked sialic acids in human-adapted strains. In disease, HA H3 drives influenza infections, prompting annual strain-specific vaccines and antibody responses targeting its variable head or conserved stalk for broader protection, though no direct small-molecule drugs target it clinically.

Other names

HAinfluenza A hemagglutinin H3H3 hemagglutinin