Hemagglutinin (HA) of influenza A virus, H5 subtype (HA)

Hemagglutinin (HA) is the primary surface glycoprotein of the influenza A virus, with the H5 subtype being a defining feature of highly pathogenic avian influenza (HPAI) strains such as H5N1 (UniProt, Wikipedia). It exists as a homotrimeric class I fusion protein that mediates two critical steps of the viral life cycle: binding to host cell sialic acid receptors and facilitating the fusion of the viral envelope with the host endosomal membrane (NIH, RCSB PDB). The H5 subtype typically exhibits a preference for alpha-2,3-linked sialic acids, which are abundant in the avian respiratory and gastrointestinal tracts and the human lower respiratory tract, contributing to the high mortality rates and severe pneumonia observed in zoonotic human infections (Wikipedia, RCSB PDB). As the major target of the host immune response, HA is the central component of vaccines and the focus of drug development efforts, including broadly neutralizing monoclonal antibodies and small-molecule fusion inhibitors (NIH, PubMed). Therapeutic interventions aim to block the receptor-binding site or the conserved stem region to prevent viral entry and spread (NIH). The protein's high rate of mutation, known as antigenic drift, presents a significant challenge for long-term vaccine efficacy and pandemic preparedness (Britannica, NIH).

Other names

H5 HAH5N1 hemagglutininHemagglutinin H5 subtypeHA1/HA2Surface glycoprotein H5H5 subtype hemagglutininH5N1 HA

Drugs targeting H5 hemagglutinin primarily work by blocking the receptor-binding site to prevent viral attachment or by binding to the conserved stem region to inhibit the pH-dependent conformational change required for membrane fusion (NIH, PubMed). Vaccines containing H5 HA induce the production of neutralizing antibodies that recognize these critical domains, thereby providing immunity against infection (FDA, NIH). Small molecules like umifenovir specifically target the fusion process by stabilizing the prefusion state of the HA protein (PubMed).