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.

Escherichia coli O157:H7 Strain EDL933 Harbors Multiple Functional Prophage-Associated Genes Necessary for the Utilization of 5- N -Acetyl-9- O -Acetyl Neuraminic Acid as a Growth Substrate

“…In addition, NanS harbors four sequence blocks (blocks I to IV) (Fig. 1B) which have been described for the SGNH superfamily of enzymes (18). All NanS-p proteins also contain a DUF303 superfamily domain and possess those conserved sequence blocks which are present in enzymes of the SGNH superfamily.…”

“…The chromosomally encoded NanS is 326 amino acids in length and carries domain of unknown function 303 (DUF303), which has been previously linked to its esterase activity (18). In addition, NanS harbors four sequence blocks (blocks I to IV) (Fig.…”

“…The residual Neu5Ac or Neu5Gc can then be separated from the glycoprotein with NanH, which is the sialidase corresponding to Bacteroidetes, and the neuraminic acids can then be used as the carbon source. Although E. coli does not express any sialidases, it still possesses the nanS gene (17,18).…”

“…In a recent review, Vimr (16) postulated that chromosomally encoded NanS of E. coli may be responsible for the use of Neu5,9Ac 2 as a carbon source. The author demonstrated by in silico analyses that pathogenic E. coli bacteria carry numerous prophage-encoded ORFs which are homologous to the chromosomal nanS (yjhS) gene, which is part of the nanCMS operon of E. coli (16)(17)(18). Landstorfer et al (19) compared the transcriptome of strain EDL933 grown in LB medium to the transcriptome present after growth in different growth media such as minimal media, radish sprouts, or feces or under different conditions such as the use of differing pH values or antibiotics.…”

Identification and Crystallographic Analysis of a New Carbohydrate Acetylesterase (SmAcE1) from Sinorhizobium meliloti

“…However, only few bacterial CEs have been identified and investigated in detail. For example, CEs from Geobacillus stearothermophilus, Butyrivibrio proteoclasticus, Neisseria gonorrhoeae, and Escherichia coli 0157 were characterized in the biochemical and structural aspects [21][22][23][24]. Most CEs belong to α/β-hydrolase family and show broad substrate specificity, but detailed reaction and substrate recognition mechanisms in the atomic levels have not been well studied yet.…”