@article {950,
	title = {Identification and mechanism of a bacterial hydrolyzing UDP-N-acetylglucosamine 2-epimerase},
	journal = {Biochemistry},
	volume = {43},
	number = {44},
	year = {2004},
	note = {ISI Document Delivery No.: 868UVTimes Cited: 13Cited Reference Count: 38},
	month = {Nov},
	pages = {14290-14298},
	type = {Article},
	abstract = {This paper reports the first identification of a fully functional hydrolyzing UDP-N-acetylglucosamine 2-epimerase from a bacterial source. The epimerase (known as SiaA or NeuC from Neisseria meningitidis MC58 group B is shown to catalyze the conversion of UDP-GlcNAc into ManNAc and UDP in the first step of sialic acid (N-acetylneuraminic acid) biosynthesis. The mechanism is proposed to involve an anti elimination of UDP to form 2-acetamidoglucal as an intermediate, followed by the syn addition of water. The observation that the alpha-anomer of ManNAc is the true product and that solvent deuterium is incorporated at C-2 is consistent with this mechanism. The use of the O-18-labeled substrate confirms that the overall hydrolysis reaction proceeds via cleavage of the C-O bond. Furthermore, the putative intermediate 2-acetamidoglucal is shown to serve as a catalytically competent substrate and is enzymatically hydrated to give ManNAc exclusively. Isotope effect studies show that cleavage of the C-H bond is not rate limiting during catalysis. Mutagenesis studies show that three active site carboxylate residues are crucial for catalysis. In two of the mutants that were studied (E122Q and D131N), 2-acetamidoglucal was released from the active site during catalysis, providing direct evidence that the enzyme is capable of catalyzing the anti elimination of UDP from UDP-GlcNAc.},
	keywords = {2-EPIMERASE/N-ACETYLMANNOSAMINE, biosynthesis, CELL-INTERACTIONS, ENZYME, ESCHERICHIA-COLI K1, KINASE, POLYSIALIC ACID, PURIFICATION, RAT-LIVER, SIALIC-ACID, STEREOCHEMISTRY},
	isbn = {0006-2960},
	url = {<Go to ISI>://000224939400045},
	author = {Murkin, A. S. and Chou, W. K. and Wakarchuk, W. W. and Tanner, M. E.}
}
@article {1023,
	title = {The NeuC protein of Escherichia coli K1 is a UDP N-acetylglucosamine 2-epimerase},
	journal = {Journal of Bacteriology},
	volume = {186},
	number = {3},
	year = {2004},
	note = {ISI Document Delivery No.: 766HUTimes Cited: 18Cited Reference Count: 43},
	month = {Feb},
	pages = {706-712},
	type = {Article},
	abstract = {The K1 capsule is an essential virulence determinant of Escherichia coli strains that cause meningitis in neonates. Biosynthesis and transport of the capsule, an alpha-2,8-linked polymer of sialic acid, are encoded by the 17-kb kps gene cluster. We deleted neuC, a K1 gene implicated in sialic acid synthesis, from the chromosome of EV36, a K-12-K1 hybrid, by allelic exchange. Exogenously added sialic acid restored capsule expression to the deletion strain (DeltaneuC), confirming that NeuC is necessary for sialic acid synthesis. The deduced amino acid sequence of NeuC showed similarities to those of UDP-N-acetylglucosamine (GlcNAc) 2-epimerases from both prokaryotes and eukaryotes. The NeuC homologue from serotype III Streptococcus agalactiae complements DeltaneuC. We cloned the neuC gene into an intein expression vector to facilitate purification. We demonstrated by paper chromatography that the purified neuC gene product catalyzed the formation of [2-C-14]acetamidoglucal and [N-C-14]acetylmannosamine (ManNAc) from UDP-[C-14]GlcNAc. The formation of reaction intermediate 2-acetamidoglucal with the concomitant release of UDP was confirmed by proton and phosphorus nuclear magnetic resonance spectroscopy. NeuC could not use GlcNAc as a substrate. These data suggest that neuC encodes an epimerase that catalyzes the formation of ManNAc from UDP-GlcNAc via a 2-acetamidoglucal intermediate. The unexpected release of the glucal intermediate and the extremely low rate of ManNAc formation likely were a result of the in vitro assay conditions, in which a key regulatory molecule or protein was absent.},
	keywords = {2-EPIMERASE/N-ACETYLMANNOSAMINE KINASE, ACETYLNEURAMINIC ACID SYNTHETASE, EXPRESSION, GENE-PRODUCT, NEISSERIA-MENINGITIDIS, POLYSACCHARIDE BIOSYNTHESIS, POLYSIALIC ACID, RAT-LIVER, SEQUENCE, SIALIC-ACID},
	isbn = {0021-9193},
	url = {<Go to ISI>://000188371600014},
	author = {Vann, W. F. and Daines, D. A. and Murkin, A. S. and Tanner, M. E. and Chaffin, D. O. and Rubens, C. E. and Vionnet, J. and Silver, R. P.}
}
