Receptor-binding properties of influenza viruses isolated from gulls.

Ducks, gulls and shorebirds represent the major hosts of influenza A viruses (IAVs) in nature, but distinctions of IAVs in different birds are not well defined. Here we characterized the receptor specificity of gull IAVs with HA subtypes H4, H6, H14, H13 and H16 using synthetic sialylglycopolymers. In contrast to duck IAVs, gull IAVs efficiently bound to fucosylated receptors and often preferred sulfated and non-sulfated receptors with Galβ1-4GlcNAc cores over the counterparts with Galβ1-3GlcNAc cores. Unlike all other IAVs of aquatic birds, H16 IAVs showed efficient binding to Neu5Acα2-6Gal-containing receptors and bound poorly to Neu5Acα2-3Galβ1-3-terminated (duck-type) receptors. Analysis of HA crystal structures and amino acid sequences suggested that the amino acid at position 222 is an important determinant of the receptor specificity of IAVs and that transmission of duck viruses to gulls and shorebirds is commonly accompanied by substitutions at this position.