Substrate Specificity of Equine and Human Influenza A Virus Sialidase to Molecular Species of Sialic Acid

Most equine influenza A viruses (IAVs) show strong binding to glycoconjugates containing N-glycolylneuraminic acid (Neu5Gc) as well as N-acetylneuraminic acid (Neu5Ac). Therefore, the progeny of equine IAV is thought to be released from the infected cell surface through removal of sialic acids by the viral sialidase. In the present study, equine IAV sialidases showed significantly lower substrate affinity than that of human IAV sialidases to artificial and natural Neu5Gc-conjugated substrates. The substrate specificity of equine IAV sialidases is in disagreement with their binding specificity to molecular species of sialic acid. The results suggest that substrate specificity of equine IAV sialidase for Neu5Ac, rather than for Neu5Gc, is important for an advantage at the early infection stage and the process of progeny virus release from the surface of infected cells.