Hemagglutinin of influenza A H5N1 virus (HA)

Hemagglutinin of influenza A H5N1 virus is a homotrimeric envelope glycoprotein that plays a central role in the pathogenicity and transmission of influenza A viruses. It is responsible for binding to host cell surface sialic acid receptors via its HA1 domain, facilitating viral attachment, and enabling viral entry by mediating fusion of the viral envelope with the endosomal membrane through a low pH-induced conformational change in its HA2 domain[1][2][3]. The HA protein is initially produced as a precursor (HA0) that must be cleaved by host proteases into two subunits, HA1 and HA2, for infectivity[1][2]. HA is the principal target of neutralizing antibodies, including those elicited by infection or vaccination, but undergoes frequent antigenic variation. The molecule is essential for infection, making it a key target for therapeutic antibodies and vaccine design, especially for highly pathogenic subtypes such as H5N1[2][3]. Owing to its role in infection and immune evasion, HA is central to influenza's pandemic potential and is a major determinant of host specificity, transmissibility, and virulence.

Other names

HemagglutininInfluenza A virus hemagglutininH5 hemagglutininH5N1 hemagglutininHA (in the context of H5N1 subtype)

Neutralizing antibodies bind to the globular head domain or to the stem region of HA, blocking sialic acid binding and/or preventing the pH-induced conformational change necessary for membrane fusion, thus inhibiting viral entry into host cells[2][3]. These can provide strain-specific or cross-strain (broadly neutralizing) activity depending on the targeted epitope[2]. Some vaccine efforts aim to elicit antibodies to conserved stem regions for broader protection.