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| {{STRUCTURE_1kvs| PDB=1kvs | SCENE= }} | | {{STRUCTURE_1kvs| PDB=1kvs | SCENE= }} |
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| '''UDP-GALACTOSE 4-EPIMERASE COMPLEXED WITH UDP-PHENOL'''
| | ===UDP-GALACTOSE 4-EPIMERASE COMPLEXED WITH UDP-PHENOL=== |
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| ==Overview==
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| UDP-galactose 4-epimerase plays a critical role in sugar metabolism by catalyzing the interconversion of UDP-galactose and UDP-glucose. Originally, it was assumed that the enzyme contained a "traditional" catalytic base that served to abstract a proton from the 4'-hydroxyl group of the UDP-glucose or UDP-galactose substrates during the course of the reaction. However, recent high-resolution X-ray crystallographic analyses of the protein from Escherichia coli have demonstrated the lack of an aspartate, a glutamate, or a histidine residue properly oriented within the active site cleft for serving such a functional role. Rather, the X-ray crystallographic investigation of the epimerase.NADH.UDP-glucose abortive complex from this laboratory has shown that both Ser 124 and Tyr 149 are located within hydrogen bonding distance to the 4'- and 3'-hydroxyl groups of the sugar, respectively. To test the structural role of Ser 124 in the reaction mechanism of epimerase, three site-directed mutant proteins, namely S124A, S124T, and S124V, were constructed and crystals of the S124A.NADH.UDP, S124A.NADH.UDP-glucose, S124T. NADH.UDP-glucose, and S124V.NADH.UDP-glucose complexes were grown. All of the crystals employed in this investigation belonged to the space group P3221 with the following unit cell dimensions: a = b = 83.8 A, c = 108.4 A, and one subunit per asymmetric unit. X-ray data sets were collected to at least 2.15 A resolution, and each protein model was subsequently refined to an R value of lower than 19.0% for all measured X-ray data. The investigations described here demonstrate that the decreases in enzymatic activities observed for these mutant proteins are due to the loss of a properly positioned hydroxyl group at position 124 and not to major tertiary and quaternary structural perturbations. In addition, these structures demonstrate the importance of a hydroxyl group at position 124 in stabilizing the anti conformation of the nicotinamide ring as observed in the previous structural analysis of the epimerase.NADH. UDP complex.
| | The line below this paragraph, {{ABSTRACT_PUBMED_9271499}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 9271499 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_9271499}} |
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| ==About this Structure== | | ==About this Structure== |
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| [[Category: Isomerase]] | | [[Category: Isomerase]] |
| [[Category: Udp-galactose]] | | [[Category: Udp-galactose]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 23:13:42 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Wed Jul 2 11:06:34 2008'' |