Influenza A virus hemagglutinin protein H1N1 subtype (HA)

Influenza hemagglutinin (HA) is a homotrimeric glycoprotein found on the surface of influenza A viruses; in H1N1 subtype viruses, HA mediates viral entry by binding to sialic acid-containing receptors on respiratory epithelial cells and facilitating fusion of the viral and host membranes under acidic conditions following endocytosis. HA is the primary antigenic determinant in influenza vaccines, and its structural variability—especially in the globular head domain—requires continual surveillance to ensure vaccine effectiveness. Antibodies targeting HA can be strain-specific or broadly neutralizing, with the latter offering potential for universal influenza vaccines. The proteins from A/Victoria/4897/2022 and A/Wisconsin/67/2022-like H1N1 strains represent vaccine-relevant variants included in recent influenza vaccines due to their prevalence and antigenic properties. HA’s role as a target for both prophylactic (vaccine-induced immunity) and therapeutic (antibody-based drugs) interventions underscores its importance in influenza infection control. If more structured data or specific variants (e.g., exact sequence or post-translational modification details) are needed, reference databases such as UniProt can provide direct accession numbers for the protein from each H1N1 strain.

Other names

Influenza hemagglutininHA proteinHemagglutinin (influenza)Influenza virus hemagglutininH1 hemagglutininH1N1 hemagglutinin

Neutralization of HA by antibodies: antibodies bind to receptor binding domain (RBD) or the stem region, blocking receptor binding and/or fusion, thus preventing infection Inhibition of conformational change required for membrane fusion (by some monoclonals)