Hemagglutinin (H7) of Influenza A virus (H7 HA)

The H7 hemagglutinin (HA) is a critical surface glycoprotein of the Influenza A virus, specifically the H7 subtype, which is a major determinant of viral infectivity and host range [1, 3]. It functions as a class I fusion protein, existing as a homotrimer on the viral envelope where each monomer consists of the HA1 (receptor-binding) and HA2 (membrane-fusion) subunits [3, 14]. The HA1 subunit mediates attachment to host cells by binding to sialic acid-containing receptors, while the HA2 subunit facilitates the fusion of the viral envelope with the host endosomal membrane following a pH-induced conformational change [3, 12]. H7 viruses are primarily avian but have caused severe human respiratory disease and conjunctivitis, with H7N9 being a notable example of a strain with high pandemic potential [9, 17]. Therapeutically, H7 HA is the primary target for neutralizing antibodies and the main component of influenza vaccines [1, 13]. Monoclonal antibodies, such as MEDI8852 and CR9114, target conserved epitopes in the HA head or stalk to prevent viral entry or fusion [1, 4]. Small molecules like umifenovir also target the HA protein to inhibit the fusion process [1, 6]. A significant challenge in targeting H7 HA is its high rate of antigenic drift, which allows the virus to escape immune recognition and necessitates the development of broadly reactive or universal vaccines [1, 16]. Additionally, the presence of a polybasic cleavage site in some H7 strains is a key marker of high pathogenicity, enabling the virus to replicate in multiple organ systems [17, 18].

Other names

H7 hemagglutininHA7H7 subtype hemagglutininInfluenza A virus H7 proteinH7N9 hemagglutinin

Inhibition of viral entry by blocking the binding of the hemagglutinin globular head to host sialic acid receptors or by preventing the pH-triggered conformational change of the hemagglutinin stalk required for membrane fusion [1, 6, 11].