Influenza A H5N1 hemagglutinin glycoprotein (HA) (HA)

The Influenza A H5N1 hemagglutinin (HA) glycoprotein is a homotrimeric surface protein essential for the infectivity of the highly pathogenic avian influenza virus [1, 8]. It consists of two subunits, HA1 and HA2; HA1 is responsible for binding to α2,3-linked sialic acid receptors on host cells, while HA2 mediates the fusion of the viral envelope with the host endosomal membrane following a pH-triggered conformational change [1, 6]. As the primary target for neutralizing antibodies, HA is the principal antigen in H5N1 vaccines, such as Audenz and Q-Pan, and is the focus of broadly neutralizing monoclonal antibodies like CR6261 and MEDI8852 [13, 14]. Mutations in the HA protein, particularly in the receptor-binding domain, are critical for the virus's potential to adapt to human hosts and achieve sustained transmission [4, 12]. Therapeutic strategies targeting HA aim to block viral entry by either preventing attachment or inhibiting the fusion process [10, 13]. The protein's structure is highly dynamic, undergoing significant structural rearrangements to facilitate the delivery of the viral genome into the host cytoplasm [1, 10]. Due to its high mutation rate, HA is subject to antigenic drift, necessitating continuous monitoring and vaccine updates to maintain efficacy against emerging clades [8, 16]. In addition to its role in viral entry, HA is a major determinant of virulence, with the multibasic cleavage site in H5N1 HA allowing for systemic infection beyond the respiratory tract [4, 9].

Other names

H5HemagglutininH5HAH5N1 HASurface glycoprotein HAH5N1 hemagglutinin

Neutralization of viral infectivity by blocking the receptor-binding site (HA1) or inhibiting the pH-dependent conformational change required for membrane fusion (HA2) [1, 13]. Vaccines induce antibodies that target these sites to prevent infection [2, 11]. Small molecules like Umifenovir bind to the HA stem to prevent fusion [10, 13].