Influenza A and B hemagglutinin (HA)

Influenza A and B hemagglutinin (HA) is a primary surface glycoprotein found on the envelope of influenza viruses, serving as the essential mediator for viral entry into host cells (UniProt P03435, P03460). It functions as a class I fusion protein that binds to sialic acid receptors on the host cell surface, triggering receptor-mediated endocytosis (PubMed: 22226355). Upon exposure to the acidic environment of the endosome, HA undergoes a massive conformational rearrangement that facilitates the fusion of the viral and endosomal membranes, allowing the viral ribonucleoproteins to enter the cytoplasm (PubMed: 11069777). As the most prominent surface antigen, HA is the primary target for neutralizing antibodies and the central component of seasonal influenza vaccines (CDC, 2023). However, the protein's high rate of antigenic drift and the potential for antigenic shift necessitate continuous surveillance and frequent vaccine updates to maintain efficacy. Therapeutic interventions targeting HA include small-molecule fusion inhibitors like umifenovir and various broadly neutralizing monoclonal antibodies currently in clinical development (PubChem CID 131411; PubMed: 31619540).

Other names

HemagglutininHAH proteinViral surface glycoproteinSialic acid-binding proteinH1N1 hemagglutininH3N2 hemagglutinin

Inhibition of viral attachment to host cell sialic acid receptors and prevention of the pH-triggered conformational change required for membrane fusion within the endosome.