Influenza A and B hemagglutinin protein (HA)

Influenza A and B hemagglutinin protein is a trimeric surface glycoprotein expressed on the viral envelope of influenza A and B viruses. It is essential for viral infectivity and pathogenesis. Each monomer of HA consists of two subunits, HA1 and HA2, generated by proteolytic cleavage of a precursor (HA0). HA1 forms the globular "head" containing the receptor-binding site, while HA2 forms the "stem" or stalk necessary for membrane fusion. HA binds sialic acid-containing receptors on host cells, mediating viral attachment and subsequent membrane fusion after endocytosis, triggered by acidic pH in the endosome[1][3][4][5]. Hemagglutinin is the principal target of neutralizing antibodies and the basis of immune protection and influenza vaccine design. It is also the main antigenic protein involved in antigenic drift (minor mutations) and shift (major recombination events)[3][5]. Multiple subtypes of HA (e.g., H1–H16 in Influenza A) define viral strains and are key markers for epidemiological surveillance.

Other names

HemagglutininInfluenza hemagglutininHA proteinInfluenza A hemagglutininInfluenza B hemagglutinin

Neutralizing antibodies: bind to either the receptor-binding site (head domain) or the stem domain, preventing viral entry or fusion[3][4][5]. Inhibitors: block conformational changes required for membrane fusion or receptor binding (under investigation).