Avian influenza A hemagglutinin subtype 5 protein (Hemagglutinin H5)

The Avian influenza A hemagglutinin subtype 5 protein (Hemagglutinin H5, or H5 HA) is a trimeric glycoprotein located on the surface of avian influenza A viruses, most notably associated with the highly pathogenic H5N1 strains. Each monomer of the trimer contains a globular head (HA1), responsible for binding to sialic acid receptors on the host cell surface, and a stalk region (HA2), which facilitates the fusion of viral and host membranes—an essential step in infection. The H5 subtype is distinguished by a polybasic cleavage site, processed by ubiquitous host proteases, and is linked to high systemic pathogenicity. The HA protein is a key target for neutralizing antibodies and vaccine development, yet its high sequence variability—particularly in the head domain—enables viral escape from host immunity. H5 HA-mediated host cell entry underpins the spread and severity of avian influenza outbreaks, with zoonotic infection and potential pandemic risk stemming from mutations that enhance human receptor binding.

Other names

Influenza A H5 hemagglutininH5 HAHA subtype 5Hemagglutinin (H5)Avian influenza hemagglutinin H5

Antibody binding blocks receptor engagement or inhibits structural rearrangement needed for membrane fusion. Inhibitors may target the fusion peptide or interfere with proteolytic activation by host proteases, preventing the HA conformational changes required for viral entry.