@article {5138,
	title = {The structure of L-ribulose-5-phosphate 4-epimerase: An aldolase-like platform for epimerization},
	journal = {Biochemistry},
	volume = {40},
	number = {49},
	year = {2001},
	note = {ISI Document Delivery No.: 500CJTimes Cited: 18Cited Reference Count: 45},
	month = {Dec},
	pages = {14763-14771},
	type = {Article},
	abstract = {The structure of L-ribulose-5 -phosphate 4-epimerase from E. coli has been solved to 2.4 Angstrom resolution using X-ray diffraction data. The structure is homo-tetrameric and displays C-4 symmetry. Each subunit has a single domain comprised of a central beta -sheet flanked on either side by layers of alpha -helices. The active site is identified by the position of the catalytic zinc residue and is located at the interface between two adjacent subunits. A remarkable feature of the structure is that it shows a very close resemblance to that of L-fuculose-1-phosphate aldolase. This is consistent with the notion that both enzymes belong to a superfamily of epimerases/aldolases that catalyze carbon-carbon bond cleavage reactions via a metal-stabilized enolate intermediate. Detailed inspection of the epimerase structure, however, indicates that despite the close overall structural similarity to class II aldolases, the enzyme has evolved distinct active site features that promote its particular chemistry.},
	keywords = {CHEMISTRY, CLASS-II, CLEAVAGE, ENZYME, ESCHERICHIA-COLI, EVOLUTION, GALACTOSE, L-FUCULOSE-1-PHOSPHATE ALDOLASE, MECHANISM, SEQUENCE, SUPERFAMILIES},
	isbn = {0006-2960},
	url = {<Go to ISI>://000172608100005},
	author = {Luo, Y. and Samuel, J. and Mosimann, S. C. and Lee, J. E. and Tanner, M. E. and Strynadka, N. C. J.}
}
@article {4298,
	title = {Epimerization via carbon-carbon bond cleavage. L-ribulose-5-phosphate 4-epimerase as a masked class II aldolase},
	journal = {Biochemistry},
	volume = {37},
	number = {16},
	year = {1998},
	note = {ISI Document Delivery No.: ZM208Times Cited: 32Cited Reference Count: 35},
	month = {Apr},
	pages = {5746-5754},
	type = {Article},
	abstract = {Studies indicating that the E. coli L-ribulose-5-phosphate 4-epimerase employs an "aldolase-like" mechanism are reported. This NAD(+)-independent enzyme epimerizes a steseocenter that does not bear an acidic proton and therefore it cannot utilize a simple deprotonation-reprotonation mechanism. Sequence similarities between the epimerase and the class II L-fuculose-1-phosphate aldolase suggest that the two may be evolutionarily related and that the epimerization may occur via carbon-carbon bond cleavage and re-formation. Conserved residues thought to provide the metal ion ligands of the epimerase have been modified using site-directed mutagenesis. The resulting mutants show low k(cat) values in addition to a reduced affinity for Zn2+. These observations serve to establish that there is a structural link between between the active site geometry of the epimerase and the aldolase. In addition, the H97N mutant was found to catalyze the condensation of dihydroxyacetone and glycolaldehyde phosphate to produce a mixture of L-ribulose-5-phosphate and D-xylulose-5-phosphate. This observation of aldolase activity establishes that the epimerase active site is capable of promoting carbon-carbon bond cleavage. Furthermore, glycolaldehyde phosphate was shown to be a competitive inhibitor of the mutant enzyme (K-t = 0.37 mM) but not of the wild-type enzyme. The mutation apparently causes the epimerase to become "leaky" and enables it to bind/generate the normal reaction intermediates from the unbound aldol cleavage products.},
	keywords = {ENZYMES, ESCHERICHIA-COLI, L-FUCULOSE-1-PHOSPHATE ALDOLASE, MECHANISM, MUTAGENESIS, ORGANIC-SYNTHESIS, PCR, PURIFICATION, SEQUENCE, SITE},
	isbn = {0006-2960},
	url = {<Go to ISI>://000073515500048},
	author = {Johnson, A. E. and Tanner, M. E.}
}
