1bxr
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(New page: 200px<br /><applet load="1bxr" size="450" color="white" frame="true" align="right" spinBox="true" caption="1bxr, resolution 2.10Å" /> '''STRUCTURE OF CARBAMO...)
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Revision as of 09:53, 20 November 2007
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STRUCTURE OF CARBAMOYL PHOSPHATE SYNTHETASE COMPLEXED WITH THE ATP ANALOG AMPPNP
Overview
Carbamoyl phosphate synthetase (CPS) catalyzes the production of carbamoyl, phosphate which is subsequently employed in the metabolic pathways, responsible for the synthesis of pyrimidine nucleotides or arginine. The, catalytic mechanism of the enzyme occurs through three highly reactive, intermediates: carboxyphosphate, ammonia, and carbamate. As isolated from, Escherichia coli, CPS is an alpha, beta-heterodimeric protein with its, three active sites separated by nearly 100 A. In addition, there are, separate binding sites for the allosteric regulators, ornithine, and UMP., Given the sizable distances between the three active sites and the, allosteric-binding pockets, it has been postulated that domain movements, play key roles for intramolecular communication. Here we describe the, structure of CPS from E. coli where, indeed, such a domain movement has, occurred in response to nucleotide binding. Specifically, the protein was, crystallized in the presence of a nonhydrolyzable analogue, AMPPNP, and, its structure determined to 2.1 A resolution by X-ray crystallographic, analysis. The B-domain of the carbamoyl phosphate synthetic component of, the large subunit closes down over the active-site pocket such that some, atoms move by more than 7 A relative to that observed in the original, structure. The trigger for this movement resides in the hydrogen-bonding, interactions between two backbone amide groups (Gly 721 and Gly 722) and, the beta- and gamma-phosphate groups of the nucleotide triphosphate. Gly, 721 and Gly 722 are located in a Type III' reverse turn, and this type of, secondary structural motif is also observed in D-alanine:D-alanine ligase, and glutathione synthetase, both of which belong to the "ATP-grasp", superfamily of proteins. Details concerning the geometries of the two, active sites contained within the large subunit of CPS are described.
About this Structure
1BXR is a Protein complex structure of sequences from Escherichia coli with MN, K, CL, ANP, ORN and NET as ligands. Active as Carbamoyl-phosphate synthase (glutamine-hydrolyzing), with EC number 6.3.5.5 Full crystallographic information is available from OCA.
Reference
Carbamoyl phosphate synthetase: closure of the B-domain as a result of nucleotide binding., Thoden JB, Wesenberg G, Raushel FM, Holden HM, Biochemistry. 1999 Feb 23;38(8):2347-57. PMID:10029528
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