Influenza A virus hemagglutinin H3 subunit (HA (H3))

Influenza A virus hemagglutinin H3 subunit is a major surface glycoprotein spike present on the viral envelope of H3 subtype influenza A viruses. It is a homotrimeric protein, each monomer comprising two subunits—HA1 and HA2—generated by proteolytic cleavage. The HA1 subunit contains the receptor-binding site, which specifically recognizes sialic acid residues on host cell surface glycoconjugates, enabling viral attachment. The HA2 subunit anchors the protein in the viral membrane and contains the fusion peptide, which mediates the pH-dependent fusion of the viral and host endosomal membranes during cell entry[1][2][3][4][5]. Hemagglutinin is the principal antigenic determinant of influenza A, dictating both infectivity and immune response. Its variable regions are frequently targeted by neutralizing antibodies (such as in vaccine responses), but antigenic drift and shift in HA can generate new viral strains capable of evading pre-existing immunity. It plays a central role in infection and is considered a major therapeutic and vaccine target[1][2][3][5].

Other names

HAHemagglutinin (H3)Influenza hemagglutinin H3H3 HA

Inhibiting viral entry (neutralizing antibodies prevent receptor binding or fusion), Vaccine-induced immune response targets HA to neutralize virus, Other