1s1m
From Proteopedia
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Crystal Structure of E. Coli CTP Synthetase
Overview
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.
About this Structure
1S1M is a Single protein structure of sequence from Escherichia coli with SO4, MG, IOD and MPD as ligands. Active as CTP synthase, with EC number 6.3.4.2 Full crystallographic information is available from OCA.
Reference
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., Endrizzi JA, Kim H, Anderson PM, Baldwin EP, Biochemistry. 2004 Jun 1;43(21):6447-63. PMID:15157079
Page seeded by OCA on Wed Nov 21 02:02:24 2007
Categories: CTP synthase | Escherichia coli | Single protein | Anderson, P.M. | Baldwin, E.P. | Endrizzi, J.A. | Kim, H. | IOD | MG | MPD | SO4 | Ammonia lyase | Ammonia tunnel | Class-ii glutamine amidotransferase | Ctp synthetase | Cytidine 5'-triphosphate synthase | Utp:ammonia ligase (adp-forming)
