PDBsum entry 2ad5

Ligase

PDB id: 2ad5

Contents

Protein chains

534 a.a. *

Ligands

ADP ×2

CTP ×2

Metals

_MG ×2

Waters ×252

* Residue conservation analysis

PDB id:

2ad5

Name:

Ligase

Title:

Mechanisms of feedback regulation and drug resistance of ctp synthetases: structure of the e. Coli ctps/ctp complex at 2.8- angstrom resolution.

Structure:

Ctp synthase. Chain: a, b. Synonym: utp--ammonia ligase, ctp synthetase. Ec: 6.3.4.2

Source:

Escherichia coli k12. Organism_taxid: 83333. Strain: k-12. Other_details: soluble cytoplasmic

Biol. unit:

Dimer (from PDB file)

Resolution:

2.80Å R-factor: 0.202 R-free: 0.277

Authors:

J.A.Endrizzi,H.Kim,P.M.Anderson,E.P.Baldwin

Key ref:

J.A.Endrizzi et al. (2005). Mechanisms of product feedback regulation and drug resistance in cytidine triphosphate synthetases from the structure of a CTP-inhibited complex. Biochemistry, 44, 13491-13499. PubMed id: 16216072 DOI: 10.1021/bi051282o

Date:

19-Jul-05 Release date: 01-Nov-05

Protein chains

P0A7E5  (PYRG_ECOLI) -  CTP synthase from Escherichia coli (strain K12)

Seq: 545 a.a.

Struc: 534 a.a.

Enzyme reactions

• Enzyme class: E.C.6.3.4.2 - Ctp synthase (glutamine hydrolyzing).
• Reaction: UTP + L-glutamine + ATP + H2O = CTP + L-glutamate + ADP + phosphate + 2 H⁺

UTP + L-glutamine + ATP + H2O = CTP (Bound ligand (Het Group name = ADP) corresponds exactly) + L-glutamate (Bound ligand (Het Group name = CTP) corresponds exactly) + ADP + phosphate + 2 × H(+)

Molecule diagrams generated from .mol files obtained from the KEGG ftp site

reference

DOI no: 10.1021/bi051282o

Biochemistry 44:13491-13499 (2005)

PubMed id: 16216072

Mechanisms of product feedback regulation and drug resistance in cytidine triphosphate synthetases from the structure of a CTP-inhibited complex.

J.A.Endrizzi, H.Kim, P.M.Anderson, E.P.Baldwin.

ABSTRACT

Cytidine triphosphate synthetases (CTPSs) synthesize CTP and regulate its intracellular concentration through direct interactions with the four ribonucleotide triphosphates. In particular, CTP product is a feedback inhibitor that competes with UTP substrate. Selected CTPS mutations that impart resistance to pyrimidine antimetabolite inhibitors also relieve CTP inhibition and cause a dramatic increase in intracellular CTP concentration, indicating that the drugs act by binding to the CTP inhibitory site. Resistance mutations map to a pocket that, although adjacent, does not coincide with the expected UTP binding site in apo Escherichia coli CTPS [EcCTPS; Endrizzi, J. A., et al. (2004) Biochemistry 43, 6447-6463], suggesting allosteric rather than competitive inhibition. Here, bound CTP and ADP were visualized in catalytically active EcCTPS crystals soaked in either ATP and UTP substrates or ADP and CTP products. The CTP cytosine ring resides in the pocket predicted by the resistance mutations, while the triphosphate moiety overlaps the putative UTP triphosphate binding site, explaining how CTP competes with UTP while CTP resistance mutations are acquired without loss of catalytic efficiency. Extensive complementarity and interaction networks at the interfacial binding sites provide the high specificity for pyrimidine triphosphates and mediate nucleotide-dependent tetramer formation. Overall, these results depict a novel product inhibition strategy in which shared substrate and product moieties bind to a single subsite while specificity is conferred by separate subsites. This arrangement allows for independent adaptation of UTP and CTP binding affinities while efficiently utilizing the enzyme surface.