Influenza A virus hemagglutinin (HA) sialic acid receptor-binding site (HA RBS)

The Influenza A virus hemagglutinin (HA) sialic acid receptor-binding site (RBS) is a critical functional domain located on the distal globular head of the HA surface glycoprotein [4, 12]. Its primary biological role is to mediate the initial attachment of the virus to host cells by binding to terminal sialic acid residues on cell-surface glycoproteins and glycolipids, a process that initiates the viral entry cycle [7, 17]. The RBS is composed of several conserved structural elements, including the 130-loop, 150-loop, 190-helix, and 220-loop, which coordinate to define the site's affinity and specificity for different sialic acid linkages [4, 12]. This specificity is a key determinant of host tropism, distinguishing between avian-like (alpha-2,3) and human-like (alpha-2,6) receptors, and is thus a major factor in pandemic potential [13, 23]. In the context of disease, the RBS is the primary target for the host's neutralizing antibody response; however, the virus frequently undergoes antigenic drift through mutations in and around the RBS to evade this immunity [12, 18]. Therapeutically, the RBS is a major focus for the development of universal vaccines and entry inhibitors [1, 10]. While most seasonal vaccines elicit strain-specific antibodies, research into broadly neutralizing antibodies (bnAbs) like C05 and CH65, as well as small-molecule mimics and peptides like the EB peptide, aims to target the conserved core of the RBS to provide protection against a wide range of influenza subtypes [6, 10, 20]. Challenges in targeting this site include glycan shielding and the need to maintain a functional balance between HA binding and neuraminidase cleavage for efficient viral fitness [5, 11, 19].

Other names

Hemagglutinin receptor-binding siteHA receptor-binding pocketSialic acid-binding siteHA1 receptor-binding domainInfluenza A virus HA RBSHA RBS

Inhibition of viral attachment to host cell sialic acid receptors, thereby preventing viral entry and subsequent replication.