@article {2140,
	title = {Mechanism and Active Site Residues of GDP-Fucose Synthase},
	journal = {Journal of the American Chemical Society},
	volume = {130},
	number = {51},
	year = {2008},
	note = {ISI Document Delivery No.: 406UOTimes Cited: 3Cited Reference Count: 37Lau, Stephen T. B. Tanner, Martin E.},
	month = {Dec},
	pages = {17593-17602},
	type = {Article},
	abstract = {L-Fucose, 6-deoxy-L-galactose, is a key component of many important glycoconjugates including the blood group antigens and the Lewis(x) ligands. The biosynthesis of GDP-L-fucose begins with the action of a dehydratase that converts GDP-D-mannose into GDP-4-keto-6-deoxy-mannose. The enzyme GDPfucose synthase, GFS, (also known as GDP-4-keto-6-deoxy-D-mannose epimerase/reductase, GMER) then converts GDP-4-keto-6-deoxy-D-mannose into GDP-L-fucose. The GFS reaction involves epimerizations at both C-3 {\textquoteright}{\textquoteright} and C-5 {\textquoteright}{\textquoteright} followed by an NADPH-dependent reduction of the carbonyl at C-4. This manuscript describes studies that elucidate the order of the epimerization steps and the roles of the active site acid/base residues responsible for the epimerizations. An active site mutant, Cys109Ser, produces GDP-6-deoxy-D-altrose as its major product indicating that C-3 {\textquoteright}{\textquoteright} epimerization occurs first and premature reduction of the GDP-4-keto-6-deoxy-D-altrose intermediate becomes competitive with GDP-L-fucose production. The same mutation results in the appearance of a kinetic isotope effect when [3 {\textquoteright}{\textquoteright}-H-2]-GDP-6-deoxy-4-keto-mannose is used as a substrate. This indicates that Cys109 is the base responsible for the deprotonation of the substrate at C-3 {\textquoteright}{\textquoteright}. The Cys109Ser mutant also catalyzes a rapid wash-in of solvent derived deuterium into the C-5 {\textquoteright}{\textquoteright} position of GDP-fucose in the presence of NADP(+). This confirms the order of epimerizations and the role of Cys109. Finally, the inactive His179Gln mutant readily catalyzes the wash-out of deuterium from the C-3 {\textquoteright}{\textquoteright} position of [3 {\textquoteright}{\textquoteright}-H-2]-GDP-6-deoxy-4-keto-mannose. Together these results strongly implicate an ordered sequence of epimerizations (C-3 {\textquoteright}{\textquoteright} followed by C-5 {\textquoteright}{\textquoteright}) and suggest that Cys109 acts as a base and His179 acts as an acid in both epimerization steps.},
	keywords = {6-DEHYDRATASE, ARABIDOPSIS-THALIANA, BIOLOGICAL FUNCTION, CATALYTIC MECHANISM, DTDP-GLUCOSE 4, ESCHERICHIA-COLI, GDP-4-KETO-6-DEOXY-D-MANNOSE EPIMERASE/REDUCTASE, HELICOBACTER-PYLORI, LEUKOCYTE ADHESION, MANNOSE 4, UDP-GALACTOSE 4-EPIMERASE},
	isbn = {0002-7863},
	url = {<Go to ISI>://000263320600076},
	author = {Lau, S. T. B. and Tanner, M. E.}
}
@article {2279,
	title = {Transient oxidation as a mechanistic strategy in enzymatic catalysis},
	journal = {Current Opinion in Chemical Biology},
	volume = {12},
	number = {5},
	year = {2008},
	note = {ISI Document Delivery No.: 375SZTimes Cited: 1Cited Reference Count: 41Tanner, Martin E.},
	month = {Oct},
	pages = {532-538},
	type = {Review},
	abstract = {Enzymes that employ a transient oxidation mechanism catalyze transformations that are overall redox neutral, but involve intermediates that have a higher oxidation state than the substrates or products. An oxidation/reduction sequence may be used directly to promote isomerization reactions or indirectly to permit the formation of stabilized intermediates such as carbanions. This review will focus on three recent examples of nicotinamide-dependent enzymes that have been found to employ transient oxidation during catalysis: ADP-L-glycero-D-manno-heptose 6-epimerase, GDP-mannose 3,5-epimerase, and the 6-phosphoglucosidases from family 4. These enzymes are remarkable in their ability to catalyze either nonstereospecific hydride transfers or multiple chemical steps within a single active site.},
	keywords = {ACTIVE-SITE, ALPHA-GLUCOSIDASE, BACILLUS-SUBTILIS, CRYSTAL-STRUCTURE, D-MANNO-HEPTOSE, D-MANNOHEPTOSE 6-EPIMERASE, DEHYDROQUINATE SYNTHASE, ESCHERICHIA-COLI, THERMOTOGA-MARITIMA, UDP-GALACTOSE 4-EPIMERASE},
	isbn = {1367-5931},
	url = {<Go to ISI>://000261134900010},
	author = {Tanner, M. E.}
}
@article {1213,
	title = {Dismutase activity of ADP-L-glycero-D-manno-heptose 6-epimerase: Evidence for a direct oxidation/reduction mechanism},
	journal = {Biochemistry},
	volume = {44},
	number = {15},
	year = {2005},
	note = {ISI Document Delivery No.: 916ZNTimes Cited: 11Cited Reference Count: 33},
	month = {Apr},
	pages = {5907-5915},
	type = {Article},
	abstract = {The first positive evidence for the utilization of a direct C-6" oxidation/reduction mechanism by ADP-L-glycero-D-manno-heptose 6-epimerase is reported here. The epimerase (HldD or AGME, formerly RfaD) operates in the biosynthetic pathway Of L-glycero-D-manno-heptose, which is a conserved sugar in the core region of lipopolysaccharide (LPS) of Gram-negative bacteria. The stereochemical inversion catalyzed by the epimerase is interesting as it occurs at an "unactivated" stereocenter that lacks an acidic C-H bond, and therefore, a direct deprotonation/reprotonation mechanism cannot be employed. Instead, the epimerase employs a transient oxidation strategy involving a tightly bound NADP(+) cofactor. A recent study ruled out mechanisms involving transient oxidation at C-4 {\textquoteright}{\textquoteright} and C-7 {\textquoteright}{\textquoteright} and supported a mechanism that involves an initial oxidation directly at the C-6 {\textquoteright}{\textquoteright} position to generate a 6"-keto intermediate (Read, J. A., Ahmed, R. A., Morrison, J. P., Coleman, W. G., Jr., Tanner, M. E. (2004) J. Am. Chem. Soc. 126, 8878-8879). A subsequent nonstereospecific reduction of the ketone intermediate can generate either epimer of the ADP-heptose. In this work, an intermediate analogue containing an aldehyde functionality at C-6 {\textquoteright}{\textquoteright}, ADP-beta-D-manno-hexodialdose, is prepared in order to probe the ability of the enzyme to catalyze redox chemistry at this position. It is found that incubation of the aldehyde with a catalytic amount of the epimerase leads to a dismutation process in which one-half of the material is oxidized to ADP-beta-D-mannuronic acid and the other half is reduced to ADP-beta-D-mannose. Transient reduction of the enzyme-bound NADP(+) was monitored by UV spectroscopy and implicates the cofactor{\textquoteright}s involvement during catalysis.},
	keywords = {ACID, ALCOHOL-DEHYDROGENASE, ALDEHYDE DEHYDROGENASE, D-MANNOHEPTOSE 6-EPIMERASE, DROSOPHILA-MELANOGASTER, EPIMERIZATION, ESCHERICHIA-COLI, GLUCOSE DEHYDROGENASE, LIVER, SITE RESIDUES, UDP-GALACTOSE 4-EPIMERASE},
	isbn = {0006-2960},
	url = {<Go to ISI>://000228425600037},
	author = {Morrison, J. P. and Read, J. A. and Coleman, W. G. and Tanner, M. E.}
}
@article {966,
	title = {The mechanism of the reaction catalyzed by ADP-beta-L-glycero-D-manno-heptose 6-epimerase},
	journal = {Journal of the American Chemical Society},
	volume = {126},
	number = {29},
	year = {2004},
	note = {ISI Document Delivery No.: 840JTTimes Cited: 14Cited Reference Count: 24},
	month = {Jul},
	pages = {8878-8879},
	type = {Article},
	keywords = {4, 6-DEHYDRATASE, BACTERIA, D-MANNOHEPTOSE 6-EPIMERASE, EPIMERIZATION, ESCHERICHIA-COLI, GLUCOSE, INSIGHTS, NUCLEOTIDE-MODIFYING ENZYMES, OUTER-MEMBRANE, UDP-GALACTOSE 4-EPIMERASE},
	isbn = {0002-7863},
	url = {<Go to ISI>://000222855300009},
	author = {Read, J. A. and Ahmed, R. A. and Morrison, J. P. and Coleman, W. G. and Tanner, M. E.}
}
@article {494,
	title = {Mechanistic aspects of enzymatic carbohydrate epimerization},
	journal = {Natural Product Reports},
	volume = {19},
	number = {3},
	year = {2002},
	note = {ISI Document Delivery No.: 566QLTimes Cited: 21Cited Reference Count: 214},
	month = {Jun},
	pages = {261-277},
	type = {Review},
	abstract = {Carbohydrate epimerases are enzymes that catalyze an inversion of stereochemistry at a stereogenic center in a sugar. This review focuses on the mechanistic strategies that are employed by this diverse family of enzymes, and is divided into the following sections: deprotonation/reprotonation, transient oxidation, cofactor independent, and mutarotation. The review is comprehensive up to Oct. 2001 and contains 216 references.},
	keywords = {2-EPIMERASE, ACETYLNEURAMINIC, ACID BIOSYNTHESIS, D-GLUCOSAMINE 2-EPIMERASE, D-MANNOHEPTOSE 6-EPIMERASE, GDP-L-FUCOSE, GLUCURONYL C-5 EPIMERASE, MANNURONAN C-5-EPIMERASE, N-ACETYLGLUCOSAMINE, RENIN-BINDING PROTEIN, SITE-DIRECTED MUTAGENESIS, UDP-GALACTOSE 4-EPIMERASE, VINELANDII},
	isbn = {0265-0568},
	url = {<Go to ISI>://000176439700001},
	author = {Samuel, J. and Tanner, M. E.}
}
@article {5208,
	title = {Sugar nucleotide-modifying enzymes},
	journal = {Current Organic Chemistry},
	volume = {5},
	number = {2},
	year = {2001},
	note = {ISI Document Delivery No.: 411FKTimes Cited: 12Cited Reference Count: 170},
	month = {Feb},
	pages = {169-192},
	type = {Review},
	abstract = {Sugar nucleotides serve as the activated forms of carbohydrates that are used in a wide range of biosynthetic pathways. Instead of building up the sugar nucleotide from the free sugar itself, nature often chooses to modify the "donor" portion of a pre-existing sugar nucleotide in a biosynthetically efficient manner. In doing so a rich variety of catalytic strategies are employed and this review focuses on recent mechanistic and structural studies of the sugar nucleotide-modifying enzymes. The review is organized around the types of reactions catalyzed and contains the following sections: Epimerases/Mutases/Decarboxylases, Eliminations and Substitutions, Oxidation and Reduction, and Substitutions on the Periphery of Sugar Nucleotides.},
	keywords = {4, 6-DEHYDRATASE, 6-DIDEOXYHEXOSES, ACETYLGLUCOSAMINE 2-EPIMERASE/N-ACETYLMANNOSAMINE, ACETYLNEURAMINIC ACID, biosynthesis, CYTIDINE DIPHOSPHATE 3, D-GLUCOSE, ESCHERICHIA-COLI K-12, FIRST 2, GDP-FUCOSE SYNTHETASE, KINASE, N-ACETYLGLUCOSAMINE, SITE-DIRECTED MUTAGENESIS, STEPS, UDP-GALACTOSE 4-EPIMERASE},
	isbn = {1385-2728},
	url = {<Go to ISI>://000167487300004},
	author = {Tanner, M. E.}
}
