Hemagglutinin (influenza A virus subtype H3N2) (HA)

Hemagglutinin (HA) is the primary surface glycoprotein of the influenza A virus H3N2 subtype, playing a critical role in viral attachment and entry into host cells [1.2.1, 1.2.2]. It functions as a homotrimeric class I fusion protein that binds to sialic acid receptors on the host cell surface via its globular head (HA1) and mediates membrane fusion in the endosome through its stalk region (HA2) upon exposure to low pH [1.2.1, 1.2.4]. H3N2 is a major cause of seasonal influenza epidemics and was responsible for the 1968 "Hong Kong flu" pandemic [1.1.2, 1.2.3]. Because HA is the main target of the host's neutralizing antibody response, it is the primary component of seasonal influenza vaccines [1.1.1, 1.2.4]. However, the protein's high rate of antigenic drift necessitates frequent vaccine updates and has spurred the development of broadly neutralizing monoclonal antibodies and small-molecule fusion inhibitors like umifenovir [1.3.1, 1.3.3]. These therapeutic strategies aim to block the initial stages of infection by preventing the virus from binding to or fusing with host membranes [1.3.4, 1.3.5].

Other names

H3 hemagglutininHAHemagglutinin HA1 chainHemagglutinin HA2 chainViral surface glycoproteinClass I viral fusion protein

Fusion inhibition; Receptor binding inhibition (neutralization)