Influenza A virus hemagglutinin, subtype H5 (H5 HA)

Influenza A virus hemagglutinin, subtype H5, is a major surface glycoprotein of the influenza virus that plays a pivotal role in viral pathogenesis and host range determination. It is responsible for the initial attachment of the virus to host cells by binding to specific sialic acid receptors, typically showing a preference for alpha-2,3-linked sialic acids found in the avian respiratory and gastrointestinal tracts (UniProt: P03452). Once internalized via endocytosis, the acidic environment of the endosome triggers a massive conformational rearrangement in the HA protein, which mediates the fusion of the viral and endosomal membranes, allowing the viral genome to enter the cytoplasm (PubMed: 16645091). Because it is the primary target for neutralizing antibodies, H5 HA is the central component of most influenza vaccines and a key focus for the development of monoclonal antibody therapies (NIH). Drugs like Umifenovir (Arbidol) target the HA-mediated fusion process, while various experimental broadly neutralizing antibodies target the conserved stem region to prevent infection across multiple strains (PubMed: 19229033). Monitoring mutations in the H5 HA protein is critical for public health, as specific amino acid substitutions can enhance binding to human-type receptors, increasing the risk of a pandemic (WHO).

Other names

Hemagglutinin H5H5 proteinHA5Influenza A virus H5 hemagglutininH5N1 hemagglutinin

Inhibition of viral entry by blocking the binding of hemagglutinin to host cell sialic acid receptors or by preventing the pH-induced conformational change required for membrane fusion (PubMed: 19229033).