Influenza A virus hemagglutinin (H5N1) (HA)

The Influenza A virus hemagglutinin (H5N1), commonly abbreviated as HA, is a glycoprotein spike on the viral envelope that mediates host cell attachment by binding sialic acid receptors, primarily alpha-2,3-linked in avian species.[1][4][5][6] It undergoes a pH-induced conformational change in endosomes, driving fusion of viral and host membranes to release the genome.[1][4][6] Encoded by genome segment 4, HA is highly antigenic, eliciting neutralizing antibodies that block binding or fusion.[1][5] In H5N1, a highly pathogenic avian influenza subtype, HA contributes to zoonotic spillover and severe human disease, with clades evolving rapidly via mutations.[1][4] Therapeutics target HA via vaccines inducing antibodies, broad-spectrum monoclonals against the conserved stem, or small molecules stabilizing pre-fusion forms, though challenges include viral evolution and narrow strain coverage.[1][4][5] HA distinguishes avian from human-adapted viruses by receptor preference, influencing pandemic potential.[1][4]

Other names

H5 hemagglutininH5 HA

Inhibition of viral entry by blocking sialic acid receptor binding (antibodies), Stem-stabilizing compounds prevent fusion pH trigger