Amino Acid Residues Contributing to the Substrate Specificity of the Influenza A Virus Neuraminidase

摘要: Influenza A viruses possess two glycoprotein spikes on the virion surface: hemagglutinin (HA), which binds to oligosaccharides containing terminal sialic acid, and neuraminidase (NA), removes acid from oligosaccharides. Hence, interplay between these receptor-binding receptor-destroying functions assumes major importance in viral replication. In contrast well-characterized role of HA host range restriction influenza viruses, there is only limited information NA substrate specificity replication among different animal species. We therefore investigated specificities for linkages N-acetyl galactose (NeuAcα2-3Gal NeuAcα2-6Gal) molecular species acids (N-acetyl N-glycolyl acids) isolated human, avian, pig hosts. Substrate assays showed that all had similar NeuAcα2-3Gal, while activities NeuAcα2-6Gal ranged marginal, as represented by avian early N2 human high (although one-third activity NeuAcα2-3Gal), swine more recent viruses. Using site-specific mutagenesis, we identified earliest virus with a detectable increase change at position 275 (from isoleucine valine) enhanced this substrate. Valine was maintained later well examination N-glycolylneuraminic (NeuGc) most low moderate substrate, exception 1967 1969, whose NeuGc The amino 431 found determine level NA: lysine conferred specificity, proline, glutamine, glutamic were associated lower specificity. Both residues lie close enzymatic active site but are not directly involved reaction mechanism. This finding suggests adaptation substrates occurs mechanism substitutions subtly alter conformation around facilitate binding acid.