Hemagglutinin (Influenza A virus H1N1 2009 pandemic strain) (HA)

Hemagglutinin (HA) is the primary surface glycoprotein of the Influenza A virus, specifically the 2009 H1N1 pandemic strain (UniProt: P03452). It functions as a class I fusion protein, responsible for binding the virus to sialic acid receptors on the host cell surface and subsequently mediating the fusion of the viral envelope with the endosomal membrane during entry (PubMed: 20110523). Because of its exposed position on the virion, HA is the principal target for neutralizing antibodies induced by infection or vaccination (NIH: National Institute of Allergy and Infectious Diseases). Therapeutic strategies focus on blocking the receptor-binding site on the HA head or the conserved fusion machinery in the HA stem (PubMed: 21307320). Monitoring the functional neutralization of this antigen via assays like hemagglutination inhibition (HAI) is the gold standard for assessing protective immunity and vaccine potency (CDC: Influenza Specimen Collection and Testing). The protein is highly susceptible to antigenic drift, necessitating frequent updates to vaccine compositions to maintain efficacy against circulating strains (PubMed: 24003181).

Other names

H1 HAHemagglutinin surface glycoprotein2009 H1N1 HAHA0H1N1pdm09 HAA/California/04/2009 HA

Vaccines induce antibodies that bind to the HA globular head to sterically hinder receptor binding or to the HA stem to prevent the conformational changes required for membrane fusion (PubMed: 21307320). Umifenovir binds to a hydrophobic pocket in the HA stem, stabilizing the prefusion state and preventing membrane fusion (PubMed: 30647444).