|1kee, resolution 2.10Å ()|
|Ligands:||, , , , , ,|
|Gene:||CARB (Escherichia coli), CARA (Escherichia coli)|
Inactivation of the Amidotransferase Activity of Carbamoyl Phosphate Synthetase by the Antibiotic Acivicin
Carbamoyl phosphate synthetase (CPS) from Escherichia coli catalyzes the formation of carbamoyl phosphate from 2 mol of ATP, bicarbonate, and glutamine. CPS was inactivated by the glutamine analog, acivicin. In the presence of ATP and bicarbonate the second-order rate constant for the inactivation of the glutamine-dependent activities was 4.0 x 10(4) m(-1) s(-1). In the absence of ATP and bicarbonate the second-order rate constant for inactivation of CPS was reduced by a factor of 200. The enzyme was protected against inactivation by the inclusion of glutamine in the reaction mixture. The ammonia-dependent activities were unaffected by the incubation of CPS with acivicin. These results are consistent with the covalent labeling of the glutamine-binding site located within the small amidotransferase subunit. The binding of ATP and bicarbonate to the large subunit of CPS must also induce a conformational change within the amidotransferase domain of the small subunit that enhances the nucleophilic character of the thiol group required for glutamine hydrolysis. The acivicin-inhibited enzyme was crystallized, and the three-dimensional structure was determined by x-ray diffraction techniques. The thiol group of Cys-269 was covalently attached to the dihydroisoxazole ring of acivicin with the displacement of a chloride ion.
Inactivation of the amidotransferase activity of carbamoyl phosphate synthetase by the antibiotic acivicin., Miles BW, Thoden JB, Holden HM, Raushel FM, J Biol Chem. 2002 Feb 8;277(6):4368-73. Epub 2001 Nov 29. PMID:11729189
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.