Hemagglutinin protein (H5 subtype)

Hemagglutinin (HA) is a surface glycoprotein found on influenza viruses, including the H5 subtype. It plays a critical role in viral entry by mediating both receptor binding and membrane fusion. The H5 subtype is most notably associated with highly pathogenic avian influenza A(H5N1), which can infect birds and, less frequently, humans. HA exists as a trimeric spike on the viral envelope, with each spike composed of three identical subunits: HA1 (receptor binding) and HA2 (fusion peptide). Avian-adapted H5 typically prefers α-2,3-linked sialic acids; however, single amino acid mutations (notably at residue 226) can shift specificity toward human-type α-2,6-linked receptors—facilitating cross-species transmission. After endocytosis into host cells, acidic pH triggers conformational changes in HA that drive fusion between viral and endosomal membranes. The high pathogenicity of certain H5 strains (notably HPAI-H5N1) is linked to their ability to be efficiently cleaved/activated by host proteases, and mutations enabling efficient binding to human-type receptors are key determinants for zoonotic potential and pandemic risk.

Other names

H5 hemagglutininHA (H5)H5N1 hemagglutinin

Target of neutralizing antibodies; target of entry inhibitors (theoretical)