1cs0
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CRYSTAL STRUCTURE OF CARBAMOYL PHOSPHATE SYNTHETASE COMPLEXED AT CYS269 IN THE SMALL SUBUNIT WITH THE TETRAHEDRAL MIMIC L-GLUTAMATE GAMMA-SEMIALDEHYDE
OverviewOverview
Carbamoyl phosphate synthetase (CPS) plays a key role in both arginine and, pyrimidine biosynthesis by catalyzing the production of carbamoyl, phosphate. The enzyme from Escherichi coli consists of two polypeptide, chains referred to as the small and large subunits. On the basis of both, amino acid sequence analyses and X-ray structural studies, it is known, that the small subunit belongs to the Triad or Type I class of, amidotransferases, all of which contain a cysteine-histidine (Cys269 and, His353) couple required for activity. The hydrolysis of glutamine by the, small subunit has been proposed to occur via two tetrahedral intermediates, and a glutamyl-thioester moiety. Here, we describe the three-dimensional, structures of the C269S/glutamine and CPS/glutamate gamma-semialdehyde, complexes, which serve as mimics for the Michaelis complex and the, tetrahedral intermediates, respectively. In conjunction with the, previously solved glutamyl-thioester intermediate complex, the, stereochemical course of glutamine hydrolysis in CPS has been outlined., Specifically, attack by the thiolate of Cys269 occurs at the Si face of, the carboxamide group of the glutamine substrate leading to a tetrahedral, intermediate with an S-configuration. Both the backbone amide groups of, Gly241 and Leu270, and O(gamma) of Ser47 play key roles in stabilizing the, developing oxyanion. Collapse of the tetrahedral intermediate leads to, formation of the glutamyl-thioester intermediate, which is subsequently, attacked at the Si face by an activated water molecule positioned near, His353. The results described here serve as a paradigm for other members, of the Triad class of amidotranferases.
About this StructureAbout this Structure
1CS0 is a Protein complex structure of sequences from Escherichia coli with MN, K, CL, PO4, ADP, ORN and NET as ligands. Active as Ligase, with EC number 6.3.5.5. Full crystallographic information is available from OCA.
ReferenceReference
The small subunit of carbamoyl phosphate synthetase: snapshots along the reaction pathway., Thoden JB, Huang X, Raushel FM, Holden HM, Biochemistry. 1999 Dec 7;38(49):16158-66. PMID:10587438
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