Hemagglutinin type H5 (H5 HA)

Hemagglutinin type H5 (H5 HA) is the primary surface glycoprotein of the H5 subtype of avian influenza A viruses, including the highly pathogenic H5N1 strain. It plays a central role in viral infectivity by mediating the attachment of the virus to host cell receptors containing alpha-2,3-linked sialic acids, which are abundant in avian tissues and the human lower respiratory tract [1, 11]. Following attachment, the protein undergoes a critical pH-dependent conformational change in the endosome to facilitate the fusion of the viral envelope with the host cell membrane, allowing the viral genome to enter the cytoplasm [4, 6]. As the major target for neutralizing antibodies, H5 HA is the focus of extensive vaccine development and novel antiviral strategies, including small-molecule fusion inhibitors like Umifenovir (Arbidol) and broadly neutralizing monoclonal antibodies that target conserved epitopes in the stem region [4, 14, 17]. Mutations in H5 HA that alter receptor specificity toward human-type alpha-2,6 linkages are a major public health concern, as they represent a key step in the adaptation of avian viruses for efficient human-to-human transmission and pandemic emergence [2, 13].

Other names

H5 hemagglutininH5 proteinAvian influenza virus H5 subtypeHemagglutinin H5 subtypeH5HAInfluenza A virus H5 hemagglutinin

Inhibition of viral entry and membrane fusion by binding to the hemagglutinin protein; specifically, inhibitors either block the receptor-binding site to prevent attachment to host cell sialic acids or bind to the conserved stem region to stabilize the prefusion conformation, thereby preventing the pH-dependent membrane fusion required for genome release.