Influenza hemagglutinin receptor-binding site (HA RBS)

The **influenza hemagglutinin receptor-binding site** (HA RBS) is a well-defined region located in the globular head domain of the hemagglutinin (HA) glycoprotein on the surface of influenza viruses[2][3][4]. The HA RBS binds specifically to sialylated glycan receptors (typically sialic acid linked to galactose in α2,3 or α2,6 configurations) present on the surface of host cells, enabling viral attachment and subsequent entry[2][3]. Structurally, the RBS is composed of conserved secondary elements (notably the 130-loop, 150-loop, 190-helix, and 220-loop) and specific residues essential for receptor binding[2][3]. Alterations in the RBS can change host specificity—for example, the switch from α2,3- to α2,6-linked sialosides is a major determinant of avian-to-human host adaptation, which underlies zoonotic and pandemic events[1][3]. The HA RBS is also a prominent target for broadly neutralizing antibodies, though its sequence variability (antigenic drift) allows the virus to escape many immune responses[2][4]. No approved small-molecule drugs directly target this site, but several experimental antibodies and universal vaccine designs aim to exploit its structural properties[2][4]. The RBS is essential for infectivity, immunogenicity, and the evolutionary dynamics of influenza viruses[1][2][3].

Other names

Hemagglutinin receptor-binding siteHA receptor-binding siteHA RBSInfluenza virus receptor-binding site

Antibodies targeting the receptor-binding site (RBS) block viral attachment to host cell sialic acid receptors, neutralizing the virus[2][4]. Mutations in the RBS can alter host specificity and resistance to antibody neutralization[3].