Influenza A virus H5N1 hemagglutinin (H5N1 HA) (H5N1 HA)

The Influenza A H5N1 hemagglutinin (HA) is the major surface glycoprotein of the H5N1 avian influenza virus and serves as the primary mediator of viral entry into host cells (UniProt P03452). The HA1 subunit of this protein forms a distal globular head that houses the receptor-binding site (RBS), a shallow pocket responsible for recognizing sialic acid receptors on the host cell surface (Stevens et al., Science, 2006). In H5N1, the RBS typically exhibits a high affinity for alpha-2,3-linked sialic acids (avian-type receptors), but specific amino acid substitutions can shift this preference toward alpha-2,6-linked sialic acids (human-type receptors), significantly increasing the risk of human-to-human transmission (Nature, 2013). This site is the most critical target for the host's neutralizing antibody response, as binding to the RBS or its periphery sterically hinders viral attachment to the respiratory epithelium. Consequently, the RBS is the focal point for vaccine design and the development of therapeutic antibodies intended to provide protection against highly pathogenic avian influenza (WHO, 2024). However, the target is characterized by high genetic plasticity, where antigenic drift allows the virus to escape immune recognition, posing a continuous challenge for long-term therapeutic efficacy.

Other names

H5 hemagglutininHA1 globular headH5N1 RBSHemagglutinin HA1 subunitInfluenza A H5N1 hemagglutinin receptor-binding site

Neutralization of viral infectivity by sterically hindering the interaction between the viral receptor-binding site and host cell sialic acid receptors.