Hemagglutinin (Influenza A virus) (HA) (HA)

Hemagglutinin (HA) is the primary surface glycoprotein of the Influenza A virus and is essential for the viral life cycle, mediating both host cell recognition and entry (UniProt P03437). It functions as a homotrimer where each monomer consists of two subunits, HA1 and HA2, which are generated by the proteolytic cleavage of a precursor (HA0). The HA1 subunit contains the globular head with the receptor-binding site that targets sialic acid residues on host respiratory epithelial cells, while the HA2 subunit contains the fusion peptide responsible for merging the viral envelope with the host endosomal membrane (Skehel & Wiley, 2000; PubMed PMC3481914). As the dominant antigen on the viral surface, HA is the central component of seasonal and pandemic influenza vaccines, designed to elicit neutralizing antibodies that block viral attachment. Therapeutic interventions targeting HA include small-molecule fusion inhibitors like Umifenovir and broadly neutralizing monoclonal antibodies that target the highly conserved stem region of the protein to provide protection across multiple influenza subtypes (DrugBank DB13609; PubMed PMC5835733).

Other names

HAHemagglutinin AInfluenza A virus hemagglutininSurface glycoproteinH1-H18 subtypesHagA (in Porphyromonas gingivalis context)

Inhibition of viral membrane fusion by stabilizing the prefusion conformation of the HA protein (e.g., Umifenovir); blocking the receptor-binding site on the HA1 subunit to prevent attachment to host cell sialic acid receptors (e.g., neutralizing antibodies) (PubMed PMC5835733; DrugBank DB13609).