1rkx: Difference between revisions

[[Image:1rkx.gif|left|200px]]<br /><applet load="1rkx" size="350" color="white" frame="true" align="right" spinBox="true"  

CDP-D-glucose 4,6-dehydratase catalyzes the conversion of CDP-D-glucose to CDP-4-keto-6-deoxyglucose in an NAD(+)-dependent manner. The product of this conversion is a building block for a variety of primary antigenic determinants in bacteria, possibly implicated directly in reactive arthritis. Here, we describe the solution of the high-resolution crystal structure of CDP-D-glucose 4,6-dehydratase from Yersinia pseudotuberculosis in the resting state. This structure represents the first CDP nucleotide utilizing dehydratase of the short-chain dehydrogenase/reductase (SDR) family to be determined, as well as the first tetrameric structure of the subfamily of SDR enzymes in which NAD(+) undergoes a full reaction cycle. On the basis of a comparison of this structure with structures of homologous enzymes, a chemical mechanism is proposed in which Tyr157 acts as the catalytic base, initiating hydride transfer by abstraction of the proton from the sugar 4'-hydroxyl. Concomitant with the removal of the proton from the 4'-hydroxyl oxygen, the sugar 4'-hydride is transferred to the B face of the NAD(+) cofactor, forming the reduced cofactor and a CDP-4-keto-d-glucose intermediate. A conserved Lys161 most likely acts to position the NAD(+) cofactor so that hydride transfer is favorable and/or to reduce the pK(a) of Tyr157. Following substrate oxidation, we propose that Lys134, acting as a base, would abstract the 5'-hydrogen of CDP-4-keto-D-glucose, priming the intermediate for the spontaneous loss of water. Finally, the resulting Delta(5,6)-glucoseen intermediate would be reduced suprafacially by the cofactor, and reprotonation at C-5' is likely mediated by Lys134.

1RKX is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Yersinia_pseudotuberculosis Yersinia pseudotuberculosis] with <scene name='pdbligand=NAD:'>NAD</scene> as [http://en.wikipedia.org/wiki/ligand ligand]. Active as [http://en.wikipedia.org/wiki/CDP-glucose_4,6-dehydratase CDP-glucose 4,6-dehydratase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=4.2.1.45 4.2.1.45] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1RKX OCA].  

[[Category: Liu, H W.]]

[[Category: Petsko, G A.]]

[[Category: Vogan, E M.]]

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