Hemagglutinin (HA) of Influenza A virus (H5N1) (HA)

The Hemagglutinin (HA) glycoprotein is a critical surface protein of the Influenza A H5N1 virus, functioning as a trimeric class I fusion protein [UniProt, 2024]. It plays a dual role in the viral life cycle: first, by mediating the binding of the virus to alpha-2,3-linked sialic acid receptors on host cells, and second, by facilitating the fusion of the viral envelope with the endosomal membrane following endocytosis [PubMed, 2021]. In H5N1, a highly pathogenic avian influenza (HPAI) strain, the HA protein contains a characteristic polybasic cleavage site that allows for systemic viral replication beyond the respiratory tract, contributing to high mortality rates [WHO, 2023]. As the principal antigen recognized by the host immune system, HA is the primary component of both seasonal and pandemic vaccines [CDC, 2024]. Therapeutic strategies targeting HA include monoclonal antibodies like MEDI8852 that bind to the conserved stem region to prevent fusion, and small molecule inhibitors such as umifenovir (Arbidol) that block the structural transitions necessary for viral entry [DrugBank, 2024].

Other names

H5Hemagglutinin surface glycoproteinHA1/HA2 complexInfluenza A virus H5N1 hemagglutinin

Neutralization of viral infectivity by blocking attachment to host sialic acid receptors or inhibiting the pH-dependent conformational change required for membrane fusion.