Hemagglutinin (H5) of Influenza A virus (H5N1) (HA)

Hemagglutinin (HA) is the primary surface glycoprotein of the H5N1 influenza virus and is essential for viral infectivity and host range determination [2, 7]. It functions as a class I fusion protein that mediates the initial binding of the virus to sialic acid receptors on host cells, specifically preferring α-2,3-linked sialic acids in avian hosts and requiring mutations to adapt to α-2,6-linked receptors in humans [7, 10]. Following attachment and endocytosis, the acidic environment of the endosome triggers a dramatic conformational change in the HA2 subunit, facilitating the fusion of the viral envelope with the host cell membrane [2, 15]. This process is critical for releasing the viral genome into the host cytoplasm to initiate replication [11, 15]. As the major antigen on the viral surface, HA is the primary target for neutralizing antibodies induced by infection or vaccination, making it the central component of H5N1 vaccines like Audenz [5, 21]. Therapeutic strategies targeting HA include monoclonal antibodies that bind to the conserved stalk region to prevent fusion and small-molecule inhibitors like Umifenovir that stabilize the prefusion state [1, 4, 15]. However, the high mutation rate of the HA gene, characterized by antigenic drift and shift, poses significant challenges for long-term vaccine efficacy and the development of broad-spectrum antivirals [9, 12]. Understanding the structural dynamics of HA is therefore vital for pandemic preparedness and the design of universal influenza therapies [6, 19].

Other names

H5 HAHemagglutinin proteinSurface glycoprotein HAHA1/HA2 subunitsInfluenza A virus H5N1 hemagglutinin

Inhibition of viral attachment to host cell sialic acid receptors and prevention of pH-dependent conformational changes required for membrane fusion within the endosome.