Hemagglutinin (HA) of Influenza A virus subtype H5N1 (HA)

Hemagglutinin (HA) of H5N1 avian influenza is a critical trimeric surface glycoprotein that mediates the initial stages of viral infection. Its primary biological functions include binding to host cell receptors—specifically α2,3-linked sialic acids prevalent in avian respiratory and gastrointestinal tracts—and facilitating the fusion of the viral envelope with the host endosomal membrane (UniProt, PDB-101). This fusion process is triggered by a low-pH-induced conformational change in the HA2 subunit after the virus is internalized via endocytosis (UniProt, ACS Publications). In the context of disease, HA is a major determinant of the high pathogenicity and zoonotic potential of H5N1, with a polybasic cleavage site in the HA0 precursor allowing for systemic viral spread in avian hosts (PMC, MDPI). As a therapeutic target, HA is the primary component of H5N1 vaccines, which aim to induce neutralizing antibodies that block viral attachment (FDA). Additionally, small molecule inhibitors like umifenovir and various monoclonal antibodies target the conserved stem or head regions of HA to prevent membrane fusion or receptor binding, respectively (PLOS One, MDPI).

Other names

H5 hemagglutininHA proteinH5N1 HAHemagglutinin H5Viral surface glycoprotein HA

Inhibition of viral attachment to sialic acid receptors, inhibition of pH-dependent membrane fusion by blocking conformational changes, or prevention of HA0 precursor cleavage into functional HA1 and HA2 subunits.