Hemagglutinin (H9) (H9 HA)

H9 hemagglutinin (HA) is the primary surface glycoprotein of the H9N2 avian influenza virus, playing a central role in the viral life cycle by mediating host cell attachment and entry [1.2.1, 1.2.3]. It functions as a trimer that recognizes and binds to sialic acid receptors on the host cell surface, with recent H9N2 strains showing an increased affinity for human-type α2,6-linked sialic acids, raising pandemic concerns [1.1.2, 1.3.3]. Following attachment, HA undergoes a low-pH-triggered conformational change in the endosome to facilitate the fusion of the viral and endosomal membranes [1.2.1, 1.2.4]. As the major target of the host immune response, HA is the primary component of influenza vaccines and a key focus for the development of neutralizing monoclonal antibodies and small-molecule entry inhibitors [1.2.1, 1.4.1]. Therapeutic strategies often target the conserved stem region to provide broad protection or the receptor-binding site in the globular head to block initial infection [1.2.3, 1.4.2]. Monitoring mutations in HA, such as those affecting glycosylation or receptor specificity, is critical for assessing zoonotic risk and ensuring vaccine efficacy [1.1.1, 1.4.4].

Other names

HAH9HemagglutininSurface glycoproteinH9N2 HA

Inhibition of viral entry by blocking receptor binding or preventing pH-induced membrane fusion.