Hemagglutinin protein of avian influenza virus subtype H5 (or H7, or other pandemic strains) (HA)

The **hemagglutinin protein** of avian influenza virus subtype H5 or H7 (or pandemic strains) is a homotrimeric glycoprotein on the viral surface, essential for viral attachment, entry, and membrane fusion[4][5]. Each monomer comprises HA1 (receptor binding domain or “head”) and HA2 (stalk and fusion domain), produced by host protease cleavage of the precursor HA0[4][3][5]. HA binds to sialic acid-containing receptors on host cells (avian strains prefer α2,3-linked sialic acids; human-adapted strains, α2,6)[1][6]. Major mutations, especially in the receptor binding site or cleavage loop, affect species specificity, pathogenicity, and the potential for pandemic spread[6][1][3]. HA is the principal target of neutralizing antibodies and the basis for most influenza vaccines[2][4][5]. Subtypes H5 and H7 are notable for their pandemic or highly pathogenic potential, in part due to the presence of polybasic cleavage sites in some strains, enabling broader tissue tropism and more severe disease[3][6]. Antigenic drift in HA drives immune evasion, necessitating constant surveillance and vaccine updates[2]. Key structural and functional insights make **hemagglutinin** a crucial therapeutic, diagnostic, and vaccine target in avian and pandemic influenza strains[2][4][5][3][1].

Other names

HemagglutininHAinfluenza hemagglutinininfluenza virus hemagglutininH5 HAH7 HAH5 hemagglutininH7 hemagglutinin

Inhibition of receptor binding (antibodies prevent attachment to sialic acid receptors); Inhibition of membrane fusion (antibodies and fusion inhibitors block conformational changes needed for fusion); Immune clearance (opsonization and neutralization by antibodies)