title: Structural and enzymatic characterization of NanS (YjhS), a 9-O-Acetyl N-acetylneuraminic acid esterase from Escherichia coli O157:H7.
abstract: There is a high prevalence of sialic acid in a number of different organisms, resulting in there being a myriad of different enzymes that can exploit it as a fermentable carbon source. One such enzyme is NanS, a carbohydrate esterase that we show here deacetylates the 9 position of 9-O-sialic acid so that it can be readily transported into the cell for catabolism. Through structural studies, we show that NanS adopts a SGNH hydrolase fold. Although the backbone of the structure is similar to previously characterized family members, sequence comparisons indicate that this family can be further subdivided into two subfamilies with somewhat different fingerprints. NanS is the founding member of group II. Its catalytic center contains Ser19 and His301 but no Asp/Glu is present to form the classical catalytic triad. The contribution of Ser19 and His301 to catalysis was confirmed by mutagenesis. In addition to structural characterization, we have mapped the specificity of NanS using a battery of substrates.
authors.affiliation: Department of Biochemistry, McGill University, Montreal, Quebec, Canada.
authors.forename: Erumbi S
authors.initials: ES
authors.lastname: Rangarajan
authors.forename: Karen M
authors.initials: KM
authors.lastname: Ruane
authors.forename: Ariane
authors.initials: A
authors.lastname: Proteau
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Schrag
authors.forename: Ricardo
authors.initials: R
authors.lastname: Valladares
authors.forename: Claudio F
authors.initials: CF
authors.lastname: Gonzalez
authors.forename: Michel
authors.initials: M
authors.lastname: Gilbert
authors.forename: Alexander F
authors.initials: AF
authors.lastname: Yakunin
authors.forename: Miroslaw
authors.initials: M
authors.lastname: Cygler
mesh_terms: D000115:Acetylesterase / Q000737:chemistry* / Q000378:metabolism*; D000595:Amino Acid Sequence; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D019453:Escherichia coli O157 / Q000737:chemistry / Q000201:enzymology* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D016415:Sequence Alignment; D012794:Sialic Acids / Q000378:metabolism*
chemical_list: D012794:Sialic Acids; C025676:9-O-acetyl-N-acetylneuraminic acid; D000115:Acetylesterase