Hemagglutinin (HA) from Influenza A virus subtype H5N1 (HA)

Hemagglutinin (HA) is the primary surface glycoprotein of the Influenza A virus subtype H5N1, playing a dual role in viral entry by mediating both attachment to host cell receptors and fusion of the viral envelope with the endosomal membrane [7, 14]. It exists as a homotrimer, where each monomer is synthesized as a precursor (HA0) that must be proteolytically cleaved into HA1 and HA2 subunits to become infectious [8, 11]. The HA1 subunit contains the receptor-binding site that specifically recognizes alpha-2,3-linked sialic acids, which are prevalent in avian respiratory and gastrointestinal tracts, while the HA2 subunit contains the fusion machinery [16, 17]. In H5N1, HA is a major determinant of virulence and host range, and its high mutation rate facilitates escape from host immune responses through antigenic drift and shift [14, 15]. As the primary target for neutralizing antibodies and vaccines, HA is a focal point for drug development, including fusion inhibitors like Umifenovir and various monoclonal antibodies that target conserved regions in the stalk to provide broad protection [3, 6, 7]. Therapeutic strategies also include host-targeting agents like DAS181, which removes the sialic acid receptors required for HA binding [2, 11]. Monitoring efficacy often involves measuring hemagglutination inhibition (HI) and virus neutralization titers to assess the immune response against specific HA variants [14, 19].

Other names

HAH5H5N1 HAHemagglutinin proteinSurface glycoprotein HAH5N1 hemagglutinin

Inhibition of viral attachment, inhibition of membrane fusion, and inhibition of proteolytic activation