Influenza A virus H5 hemagglutinin (H5 HA)

Influenza A virus H5 hemagglutinin is a trimeric surface glycoprotein essential for viral infectivity, responsible for both binding the virus to sialic acid-containing receptors on host cells and mediating the subsequent fusion of viral and endosomal membranes during entry. The H5 subtype refers to the specific antigenic type of hemagglutinin, commonly associated with highly pathogenic avian influenza strains such as H5N1, which can occasionally infect humans. Hemagglutinin is expressed as an HA0 precursor that must be cleaved into HA1 and HA2 subunits by host proteases to become fusion-competent; the structure and accessibility of this cleavage site are major determinants of pathogenicity. H5 HA is highly variable but certain sites—particularly in the stem region—are conserved and have been the focus of broadly neutralizing antibody development. Due to its central role in host specificity, transmissibility, and membrane fusion, H5 hemagglutinin is a major therapeutic and diagnostic target in influenza research, vaccine design, and antibody therapies.

Other names

hemagglutinin H5H5 subtype hemagglutininH5 HAHA H5H5N1 hemagglutinin

Neutralizing antibodies typically bind to the stem or head domains of HA, blocking conformational changes required for membrane fusion or masking receptor binding sites to prevent viral entry. Small molecule fusion inhibitors (experimental) prevent pH-triggered conformational change required for viral membrane fusion.