Hemagglutinin protein, H5N1 influenza A virus (HA (H5N1))

The **Hemagglutinin protein (HA)** of the H5N1 influenza A virus is a trimeric surface glycoprotein essential for viral entry into host cells. It mediates two critical steps: binding of the virus to sialic acid-containing receptors on the host cell surface and subsequent membrane fusion, which allows the viral genome to enter the host cytoplasm[1][3]. HA is synthesized as a precursor (HA0) that is post-translationally cleaved into HA1 and HA2 subunits; this cleavage is necessary for activation and is a key determinant of viral pathogenicity—with the polybasic cleavage site associated with high pathogenicity in H5N1[3][5]. The receptor-binding domain is found within HA1, while the fusion peptide is in HA2[1][3]. HA is also a major antigenic target of the host immune response and the main component of influenza vaccines[1][3]. In H5N1 viruses, amino acid changes in hemagglutinin can alter pathogenicity, transmissibility, and host range, and the protein's acid stability regulates fusion activation and therefore influences pathogenesis and environment persistence[3][5]. There are no approved small-molecule HA inhibitors in clinical use; current targeting is via vaccine-generated immunity or experimental monoclonal antibodies. The HA of H5N1 is a validated, structurally and functionally characterized therapeutic and vaccine target[1][3][5].

Other names

Hemagglutinin (HA) glycoproteinInfluenza A virus H5N1 HAH5-HA

Drugs/antibodies block receptor binding or inhibit conformational changes needed for membrane fusion