1a9x

File:1a9x.gif

spinqualitylabelsall models 1a9x, resolution 1.8Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

CARBAMOYL PHOSPHATE SYNTHETASE: CAUGHT IN THE ACT OF GLUTAMINE HYDROLYSIS

OverviewOverview

Carbamoyl phosphate synthetase from Escherichia coli catalyzes the, production of carbamoyl phosphate from two molecules of Mg2+ATP, one, molecule of bicarbonate, and one molecule of glutamine. The enzyme, consists of two polypeptide chains referred to as the large and small, subunits. While the large subunit provides the active sites responsible, for the binding of nucleotides and other effector ligands, the small, subunit contains those amino acid residues that catalyze the hydrolysis of, glutamine to glutamate and ammonia. From both amino acid sequence analyses, and structural studies it is now known that the small subunit belongs to, the class I amidotransferase family of enzymes. Numerous biochemical, studies have suggested that the reaction mechanism of the small subunit, proceeds through the formation of the glutamyl thioester intermediate and, that both Cys 269 and His 353 are critical for catalysis. Here we describe, the X-ray crystallographic structure of carbamoyl phosphate synthetase, from E. coli in which His 353 has been replaced with an asparagine, residue. Crystals employed in the investigation were grown in the presence, of glutamine, and the model has been refined to a crystallographic, R-factor of 19.1% for all measured X-ray data from 30 to 1.8 A resolution., The active site of the small subunit clearly contains a covalently bound, thioester intermediate at Cys 269, and indeed, this investigation provides, the first direct structural observation of an enzyme intermediate in the, amidotransferase family.

About this StructureAbout this Structure

1A9X is a Protein complex structure of sequences from Escherichia coli with MN, K, PO4, CL, ADP, ORN and NET as ligands. Structure known Active Site: . Full crystallographic information is available from OCA.

ReferenceReference

Carbamoyl phosphate synthetase: caught in the act of glutamine hydrolysis., Thoden JB, Miran SG, Phillips JC, Howard AJ, Raushel FM, Holden HM, Biochemistry. 1998 Jun 23;37(25):8825-31. PMID:9636022

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