1S1M

Crystal Structure of E. Coli CTP Synthetase

Summary for 1S1M

• Entry DOI: 10.2210/pdb1s1m/pdb
• Descriptor: CTP synthase, SULFATE ION, MAGNESIUM ION, ... (6 entities in total)
• Functional Keywords: ctp synthetase, utp:ammonia ligase (adp-forming), cytidine 5'-triphosphate synthase, ammonia lyase, class-ii glutamine amidotransferase, ammonia tunnel, ligase
• Biological source: Escherichia coli
• Total number of polymer chains: 2
• Total formula weight: 123642.24

Authors

Endrizzi, J.A.,Kim, H.,Anderson, P.M.,Baldwin, E.P. (deposition date: 2004-01-06, release date: 2004-06-15, Last modification date: 2024-02-14)

Primary citation

Endrizzi, J.A.,Kim, H.,Anderson, P.M.,Baldwin, E.P.
Crystal Structure of Escherichia coli Cytidine Triphosphate Synthetase, a Nucleotide-Regulated Glutamine Amidotransferase/ATP-Dependent Amidoligase Fusion Protein and Homologue of Anticancer and Antiparasitic Drug Targets
Biochemistry, 43:6447-6463, 2004

PubMed Abstract: Cytidine triphosphate synthetases (CTPSs) produce CTP from UTP and glutamine, and regulate intracellular CTP levels through interactions with the four ribonucleotide triphosphates. We solved the 2.3-A resolution crystal structure of Escherichia coli CTPS using Hg-MAD phasing. The structure reveals a nearly symmetric 222 tetramer, in which each bifunctional monomer contains a dethiobiotin synthetase-like amidoligase N-terminal domain and a Type 1 glutamine amidotransferase C-terminal domain. For each amidoligase active site, essential ATP- and UTP-binding surfaces are contributed by three monomers, suggesting that activity requires tetramer formation, and that a nucleotide-dependent dimer-tetramer equilibrium contributes to the observed positive cooperativity. A gated channel that spans 25 A between the glutamine hydrolysis and amidoligase active sites provides a path for ammonia diffusion. The channel is accessible to solvent at the base of a cleft adjoining the glutamine hydrolysis active site, providing an entry point for exogenous ammonia. Guanine nucleotide binding sites of structurally related GTPases superimpose on this cleft, providing insights into allosteric regulation by GTP. Mutations that confer nucleoside drug resistance and release CTP inhibition map to a pocket that neighbors the UTP-binding site and can accommodate a pyrimidine ring. Its location suggests that competitive feedback inhibition is affected via a distinct product/drug binding site that overlaps the substrate triphosphate binding site. Overall, the E. coli structure provides a framework for homology modeling of other CTPSs and structure-based design of anti-CTPS therapeutics.

PubMed: 15157079
DOI: 10.1021/bi0496945

Experimental method

X-RAY DIFFRACTION (2.3 Å)