Length and density of α2-3 sialyllactose-containing chains on glycopolymers determine receptor binding of avian influenza viruses.

Influenza A viruses use host sialoglycans for attachment via hemagglutinin (HA) and hydrolyze them upon budding via neuraminidase (NA). The HAs of some human isolates prefer extended and branched glycans for binding; however, the preference of avian influenza viruses (AIVs) for these glycans is poorly understood. This study addressed the glycan-binding preferences of HA and AIV particles by using a series of sialoglycopolymers with various glycan representations and densities. Glycan extension was mimicked by linking the terminal sialyllactose with subsequent polyethylene glycol chains, and glycan density was further controlled by polymerizing the glycomonomers with the corresponding numbers of acrylamide spacers. Recombinant HAs and particles of two AIVs were used in a solid-phase direct binding assay with the aforementioned sialoglycopolymers. Both recombinant HAs preferred higher-density glycans, but did not bind to the homopolymer with the highest density. These observations suggested that most sialyllactoses in the highest-density polymer were not involved in the interaction with HA, whereas extremely high-density sialyllactoses negatively impacted HA binding. Additionally, binding analysis using viral particles demonstrated that HA clusters on the particles compensated for weak binding to low-density glycans by employing multivalent HA-glycan interactions. This approach enabled the evaluation of the complex nature of viral particles as macromolecules in glycan binding and the clustering effect of glycan density in a glycopolymer. These findings suggest elaborate protein-carbohydrate interactions via multivalent receptor-ligand binding between AIV particles and sialoglycans.