@article {1279,
	title = {The enzymes of sialic acid biosynthesis},
	journal = {Bioorganic Chemistry},
	volume = {33},
	number = {3},
	year = {2005},
	note = {ISI Document Delivery No.: 931CJTimes Cited: 36Cited Reference Count: 59},
	month = {Jun},
	pages = {216-228},
	type = {Review},
	abstract = {The sialic acids are a family of nine carbon a-keto acids that play a wide variety of biological roles in nature. In mammals, they are found at the distal ends of cell surface glycoconjugates, and thus are major determinants of cellular recognition and adhesion events. In certain strains of pathogenic bacteria, they are found in capsular polysaccharides that mask the organism from the immune system by mimicking the exterior of a mammalian cell. This review outlines recent developments in the understanding of the two main enzymes responsible for the biosynthesis of the sialic acid, N-acetylneuraminic acid. The first, a hydrolyzing UDP-N-acetyl-glucosamine 2-epimerase, generates N-acetylmannosamine and UDP from UDP-N-acetylglucosamine. The second, sialic acid synthase, generates either N-acetylneuraminic acid (bacteria) or N-acetylneuraminic acid 9-phosphate (mammals) in a condensation reaction with phosphoenolpyruvate. An emphasis is placed on an understanding of the mechanistic and structural features of these enzymes. (c) 2005 Elsevier Inc. All rights reserved.},
	keywords = {2-EPIMERASE/N-ACETYLMANNOSAMINE KINASE, BIFUNCTIONAL KEY ENZYME, biosynthesis, ESCHERICHIA-COLI K1, FIRST 2, KDO8P SYNTHASE, MECHANISM, N-ACETYLGLUCOSAMINE 2-EPIMERASE, N-acetylmannosamine, N-ACETYLNEURAMINIC ACID, NEISSERIA-MENINGITIDIS, PHOSPHATE, phosphoenolpyruvate, RAT-LIVER, sialic acid synthase, STEPS, SYNTHASE GENE, UDP-GlcNAc 2-epimerase},
	isbn = {0045-2068},
	url = {<Go to ISI>://000229463100007},
	author = {Tanner, M. E.}
}
@article {972,
	title = {Active site mutants of the "non-hydrolyzing" UDP-N-acetylglucosamine 2-epimerase from Escherichia coli},
	journal = {Biochimica Et Biophysica Acta-Proteins and Proteomics},
	volume = {1700},
	number = {1},
	year = {2004},
	note = {ISI Document Delivery No.: 833VCTimes Cited: 4Cited Reference Count: 26},
	month = {Jul},
	pages = {85-91},
	type = {Article},
	abstract = {The "non-hydrolyzing" bacterial UDP-N-acetylglucosamine 2-epimerase catalyzes the reversible interconversion of UDP-N-acetylglucosarnine (UDP-GlcNAc) and UDP-N-acetylmannosamine (UDP-ManNAc). This homodimeric enzyme is allosterically activated by its substrate, UDP-GlcNAc, and it is thought that one subunit plays a regulatory role, while that of the other plays a catalytic role. In this work, five active site mutants were prepared (D95N, E117Q, E131Q, K15A, and H213N) and analyzed in terms of their effects on binding, catalysis, and allosteric regulation. His213 appears to play a role in UDP binding and may also assist in catalysis and/or regulation, but is not a key catalytic residue. Lys15 appears to be quite important for binding. All three of the carboxylate mutants showed dramatic decreases in the value of k(cat) but relatively unaffected values of Km. Thus, these residues are playing key roles in catalysis and/or regulation. In the case of E117Q, the reaction intermediates are released into solution at a rate comparable to that of the overall catalysis. This may indicate that Glu117 plays the role as an acid/base catalyst in the second step of the UDP-GlcNAc epimerization reaction. All three carboxylate mutants were found to exhibit impaired allosteric control. (C) 2004 Elsevier B.V. All rights reserved.},
	keywords = {2-acetamidoglucal, 2-EPIMERASE/N-ACETYLMANNOSAMINE KINASE, ACID BIOSYNTHESIS, allosteric regulation, enterobacterial common antigen, EPIMERIZATION, HOMOLOGY, MECHANISM, MUTAGENESIS, RAT-LIVER, SEQUENCE, sialic acid, STREPTOCOCCUS-PNEUMONIAE, TRANSFERASES, UDP-N-acetylmannosamine},
	isbn = {1570-9639},
	url = {<Go to ISI>://000222367400011},
	author = {Samuel, J. 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.}
}
@article {593,
	title = {Sialic acid biosynthesis: Stereochemistry and mechanism of the reaction catalyzed by the mammalian UDP-N-acetylglucosamine 2-epimerase},
	journal = {Journal of the American Chemical Society},
	volume = {125},
	number = {9},
	year = {2003},
	note = {ISI Document Delivery No.: 649YPTimes Cited: 19Cited Reference Count: 44},
	month = {Mar},
	pages = {2455-2461},
	type = {Article},
	abstract = {The bifunctional enzyme, UDP-N-acetylglucosamine 2-epimerase/ManNAc kinase, catalyzes the first two steps in the biosynthesis of the sialic acids in mammals. The epimerase domain converts UDP-GlcNAc into ManNAc and UDP. This paper demonstrates that a-ManNAc is the first formed anomer and therefore the reaction proceeds with a net retention of configuration at C-1. Studies in deuterated buffer show that solvent-derived deuterium is quantitatively incorporated into the C-2 position of the product during catalysis, but it is not incorporated into the remaining pool of substrate. This indicates that the inversion of stereochemistry is ultimately brought about by the removal and replacement of a proton at C-2 and is consistent with a two-base mechanism. Studies with O-18-labeled UDP-GlcNAc show that the anomeric oxygen of the glycosyl phosphate bond departs with the UDP product and therefore the net hydrolysis reaction involves C-O bond cleavage. Incubation of the putative intermediate, 2-acetamidoglucal, with the enzyme resulted in a slow hydration reaction to give the product, ManNAc. Additional kinetic isotope effect and positional isotope exchange (PIX) experiments address the nature of the rate-determining step of the reaction and show that C-H bond cleavage is not rate limiting. Overall, these results support a reaction mechanism involving an anti-elimination of UDP to give 2-acetamidoglucal, followed by a syn-addition of water.},
	keywords = {2-EPIMERASE/N-ACETYLMANNOSAMINE KINASE, BIFUNCTIONAL ENZYME CATALYZES, BINDING, CELL-SURFACE SIALYLATION, EPIMERIZATION, FIRST 2 STEPS, GLUTAMATE RACEMASE, POSITIONAL ISOTOPE EXCHANGE, RAT-LIVER},
	isbn = {0002-7863},
	url = {<Go to ISI>://000181235800030},
	author = {Chou, W. K. and Hinderlich, S. and Reutter, W. and Tanner, M. E.}
}
@article {4750,
	title = {The structure of UDP-N-acetylglucosamine 2-epimerase reveals homology to phosphoglycosyl transferases},
	journal = {Biochemistry},
	volume = {39},
	number = {49},
	year = {2000},
	note = {ISI Document Delivery No.: 383GTTimes Cited: 58Cited Reference Count: 48},
	month = {Dec},
	pages = {14993-15001},
	type = {Article},
	abstract = {Bacterial UDP-N-acetylglucosamine 2-epimerase catalyzes the reversible epimerization at C-2 of UDP-N-acetylglucosamine (UDP-GlcNAc) and thereby provides bacteria with UDP-N-acetylmannosamine (UDP-ManNAc), the activated donor of ManNAc residues. ManNAc is critical for several processes in bacteria, including formation of the antiphagocytic capsular polysaccharide of pathogens such as Streptococcus pneumoniae types 19F and 19A. We have determined the X-ray structure (2.5 Angstrom) of UDP-GlcNAc 2-epimerase with bound UDP and identified a previously unsuspected structural homology with the enzymes glycogen phosphorylase and T4 phage beta -glucosyltransferase. The relationship to these phosphoglycosyl transferases is very intriguing in terms of possible similarities in the catalytic mechanisms. Specifically, this observation is consistent with the proposal that the UDP-GlcNAc 2-epimerase-catalyzed elimination and re-addition of UDP to the glycal intermediate may proceed through a transition state with significant oxocarbenium ion-like character. The homodimeric epimerase is composed of two similar alpha/beta/alpha sandwich domains with the active site-located in the deep cleft at the domain interface. Comparison of the multiple copies in the asymmetric unit has revealed that the epimerase can undergo a 10 degrees interdomain rotation that is implicated in the regulatory mechanism. A structure-based sequence alignment has identified several basic residues in the active site that may be involved in the proton transfer at C-2 or stabilization of the proposed oxocarbenium ion-like transition state. This insight into the structure of the bacterial epimerase is applicable to the homologous N-terminal domain of the bifunctional mammalian UDP-GlcNAc "hydrolyzing" 2-epimerase/ManNAc kinase that catalyzes the rate-determining step in the sialic acid biosynthetic pathway.},
	keywords = {2-EPIMERASE/N-ACETYLMANNOSAMINE KINASE, ACETYLNEURAMINIC ACID BIOSYNTHESIS, BETA-GLUCOSYLTRANSFERASE, BIFUNCTIONAL ENZYME CATALYZES, CELL-SURFACE SIALYLATION, DNA MODIFYING, enterobacterial common antigen, ENZYME, FIRST 2 STEPS, GLYCOGEN-PHOSPHORYLASE, RAT-LIVER},
	isbn = {0006-2960},
	url = {<Go to ISI>://000165875300001},
	author = {Campbell, R. E. and Mosimann, S. C. and Tanner, M. E. and Strynadka, N. C. J.}
}
