Hemagglutinin protein of H5N1 influenza A virus (HA)

Hemagglutinin (HA) is the primary surface glycoprotein of the H5N1 influenza A virus and is essential for viral entry into host cells. It functions as a trimeric protein that recognizes and binds to alpha-2,3-linked sialic acid receptors, which are prevalent in the lower respiratory tract of humans and the intestinal tract of birds (UniProt: P03466). Following attachment and endocytosis, the acidic environment of the endosome triggers a dramatic conformational change in the HA2 subunit, mediating the fusion of the viral and endosomal membranes (PubMed: 16410849). Because HA is the main target for neutralizing antibodies, it is the key antigen used in H5N1 vaccines, such as Audenz (FDA). However, the protein's high rate of antigenic drift and the potential for antigenic shift necessitate constant monitoring and the development of universal flu vaccines or small-molecule fusion inhibitors like Umifenovir (PubChem: CID 131411). Targeting the conserved stem region of HA is a major focus for developing broadly neutralizing antibodies that could protect against multiple influenza strains (PubMed: 19229033).

Other names

HAH5HemagglutininH5 HAInfluenza A virus H5N1 hemagglutinin

Inhibition of viral attachment to host sialic acid receptors, blockade of pH-dependent membrane fusion, and neutralization of viral particles (PubMed: 19229033, PubChem: CID 131411).