Influenza A virus hemagglutinin H5 (H5N1 subtype) (HA (H5))

Influenza A virus hemagglutinin H5 is a trimeric glycoprotein on the surface of influenza A viruses of the H5N1 subtype and is a key mediator of viral entry into host cells[1][2][3]. HA (H5) binds sialic acid–containing receptors on the respiratory epithelial cells of birds and, less efficiently, humans, facilitating endocytosis of the virus and subsequent fusion of the viral and host membranes in the low pH environment of the endosome[1][3][4]. The HA protein must be cleaved by host proteases into its HA1 and HA2 subunits to become fusion-competent, a feature that also influences pathogenicity; highly pathogenic strains have cleavage sites more susceptible to ubiquitous host proteases, broadening tissue tropism and severity[1]. HA is the principal antigen against which host neutralizing antibodies are generated, making it a focus for vaccine and therapeutic development[1][3]. Mutations in the H5 gene can increase infectivity and host range, including human adaptation, and are closely monitored as markers for pandemic potential[1][2][3][5].

Other names

Influenza hemagglutinin H5H5 hemagglutininH5N1 HAHA H5 subtype

Fusion inhibition (drugs that block conformational change or fusion peptide exposure) Receptor binding inhibition (antibodies or molecules blocking HA from engaging sialic acid) Antigenic neutralization (neutralizing antibodies prevent virus attachment or membrane fusion)