View source for 1kvs

[[Image:1kvs.gif|left|200px]]<br /><applet load="1kvs" size="350" color="white" frame="true" align="right" spinBox="true" 
caption="1kvs, resolution 2.15&Aring;" />
'''UDP-GALACTOSE 4-EPIMERASE COMPLEXED WITH UDP-PHENOL'''<br />

==Overview==
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.

==About this Structure==
1KVS is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli] with <scene name='pdbligand=NA:'>NA</scene>, <scene name='pdbligand=NAD:'>NAD</scene>, <scene name='pdbligand=UPG:'>UPG</scene> and <scene name='pdbligand=PEG:'>PEG</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/UDP-glucose_4-epimerase UDP-glucose 4-epimerase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=5.1.3.2 5.1.3.2] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1KVS OCA]. 

==Reference==
Molecular structures of the S124A, S124T, and S124V site-directed mutants of UDP-galactose 4-epimerase from Escherichia coli., Thoden JB, Gulick AM, Holden HM, Biochemistry. 1997 Sep 2;36(35):10685-95. PMID:[http://ispc.weizmann.ac.il//pmbin/getpm?pmid=9271499 9271499]
[[Category: Escherichia coli]]
[[Category: Single protein]]
[[Category: UDP-glucose 4-epimerase]]
[[Category: Gulick, A.]]
[[Category: Holden, H M.]]
[[Category: Thoden, J B.]]
[[Category: NA]]
[[Category: NAD]]
[[Category: PEG]]
[[Category: UPG]]
[[Category: epimerase]]
[[Category: galactose metabolism]]
[[Category: isomerase]]
[[Category: udp-galactose]]

''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 13:38:25 2008''