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

The H5N1 hemagglutinin protein is a glycosylated surface glycoprotein of highly pathogenic avian influenza A viruses responsible for binding to sialic acid receptors on host cells, mediating viral entry via membrane fusion, and determining host range and tissue tropism. The protein is expressed as a precursor HA0, cleaved into two subunits—HA1 (receptor-binding and antigenic domains) and HA2 (fusion machinery)—which assemble into a trimer. The HA1 subunit contains the receptor-binding domain (RBD) and several antigenic sites recognized by neutralizing antibodies. Mutations, especially in the stalk region and RBD, modulate pathogenicity, host specificity, acid stability, and transmissibility. HA surface exposure makes it the primary target for neutralizing antibodies and experimental vaccines, though its variability and rapid evolution pose major therapeutic challenges. Its function is essential for infection, and disruption of its activity can neutralize viral infectivity.

Other names

H5 hemagglutininInfluenza A H5N1 hemagglutininHA (when context is clear as subtype H5N1)Hemagglutinin H5Influenza hemagglutinin (when referring to H5N1 specifically)

Neutralizing antibodies block receptor binding or fusion; Fusion inhibitors stabilize the prefusion conformation or block the pH-dependent change; Small molecules or peptides disrupt the trimer interface or fusion activity