Background: Hemagglutinin (HA) binds to sialic acid-containing receptors on the cell surface bringing about the attachment of the virus particle to the cell. Plays a major role in the determination of host range restriction and virulence. Class I viral fusion protein. Responsible for penetration of the virus into the cell cytoplasm by mediating the fusion of the membrane of the endocytosed virus particle with the endosomal membrane. Low pH in endosomes induce an irreversible conformational change in HA2 releasing the fusion hydrophobic peptide. Several trimers are required to form a competent fusion pore.
HAo is consists of 584 amino acids with molecular mass of 63275. In natural infection inactive HA is matured into HA1 and HA2. By the sequence similarity it is indicated to be palmitoylated.