Hemagglutinin (HA) of Influenza A virus subtype H7N9 (HA)

Hemagglutinin (HA) is the primary surface glycoprotein of the Influenza A virus H7N9 subtype, serving as a critical mediator of viral entry into host cells. It functions by binding to sialic acid receptors on the cell surface—specifically favoring avian-type alpha 2-3 linkages, though mutations can shift preference toward human-type alpha 2-6 linkages—and subsequently facilitating membrane fusion in the endosome (NIH, 2018). This protein is a major determinant of viral pathogenicity and host range, with the H7N9 subtype notably causing severe respiratory illness and high mortality rates in humans (Wikipedia, 2022). HA is the principal target for neutralizing antibodies and is the central component of seasonal and pandemic influenza vaccines (Pirbright Institute, 2018). Therapeutic interventions include monoclonal antibodies like MEDI8852 and VIS-410 that target the conserved stalk region, as well as small molecules like umifenovir that inhibit the conformational changes required for fusion (ASM, 2019). The protein's structure consists of the HA1 subunit for receptor binding and the HA2 subunit for membrane fusion, both of which are targets for drug development (MDPI, 2023). However, the target's high rate of antigenic drift and the emergence of highly pathogenic avian influenza (HPAI) strains with polybasic cleavage sites present ongoing challenges for vaccine efficacy and pandemic preparedness (CDC, 2019). Monitoring HA mutations is essential for identifying strains with increased human-to-human transmission potential (NIH, 2023).

Other names

H7 HAH7N9 hemagglutininHemagglutinin glycoproteinInfluenza A virus H7N9 HAH7N9 surface glycoprotein

Inhibition of viral entry by blocking receptor binding or preventing pH-dependent membrane fusion through stabilization of the hemagglutinin neutral pH conformation.