1kvr: Difference between revisions

==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==

1KVR 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 NA, NAD, UDP, EDO and PEG 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://ispc.weizmann.ac.il/oca-bin/ocashort?id=1KVR OCA].

 

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: Single protein]]

[[Category: UDP-glucose 4-epimerase]]

[[Category: Gulick, A.]]

[[Category: Holden, H.M.]]

[[Category: Thoden, J.B.]]

[[Category: EDO]]

[[Category: NA]]