Influenza virus hemagglutinin protein subtype H3 (HA (H3))

Influenza virus hemagglutinin protein subtype H3 is a trimeric glycoprotein located on the surface of the influenza A virus, essential for viral infectivity and pathogenesis. It mediates the initial attachment of the virus to host cell receptors through binding to sialic acid residues on glycoproteins or glycolipids, as well as the subsequent fusion of the viral and host endosomal membranes upon exposure to low pH in the endosome, thereby enabling the viral genome to enter the host cytoplasm[5][1][2][3]. HA exists as a homotrimer, with each monomer comprising two subunits: HA1, which is responsible for receptor binding and antigenic diversity, and HA2, which contains the fusion peptide and anchors the HA to the viral envelope[2][3][5]. Proteolytic cleavage of the HA0 precursor into HA1 and HA2 is required for the membrane fusion activity—a process regulated by the type of cleavage site, which contributes to pathogenicity[2][3]. The H3 subtype is one of several antigenic types of influenza A hemagglutinin, responsible for human seasonal flu outbreaks and pandemics, and is a major antigenic determinant used in current vaccine formulations. Multiple antigenic sites on H3 HA are major targets for neutralizing antibodies, but frequent mutations (antigenic drift) and occasional reassortment events (antigenic shift) create challenges for immunity and therapeutic targeting[2][3][5].

Other names

influenza H3 hemagglutininH3 HAhemagglutinin H3HA H3influenza A H3 HA

Inhibition of receptor binding; Inhibition of membrane fusion; Neutralization via antibody binding to antigenic sites on HA