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Human CTP synthetase 2 - glutaminase domain

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PDB Code 2VKT Target Class Nucleotide metabolism Target CTPS2 Alias CTPS2, DKFZp686C17207, FLJ43358, MGC32997 Disease Area/Function cancer Date Deposited Dec 28 2007 Authors M.WELIN, L.TRESAUGUES, C.H.ARROWSMITH, H.BERGLUND, R.D.BUSAM, R.COLLINS, L.G.DAHLGREN, A.M.EDWARDS, S.FLODIN, A.FLORES, S.GRASLUND, M.HAMMARSTROM, M.D.HERMAN, I.JOHANSSON, A.KALLAS, T.KARLBERG, T.KOTENYOVA, L.LEHTIO, M.MOCHE, M.E.NILSSON, T.NYMAN, C.PERSSON, J.SAGEMARK, L.SVENSSON, A.G.THORSELL, S.VAN DEN BERG, J.WEIGELT, P.NORDLUND. Related Structure 2V4U, 3IHL

About this structure

CTP synthetase (CTPS, EC 6.3.4.2) is a rate-limiting enzyme in the synthesis of cytosine nucleotides, which play an important role in various metabolic processes and provide the precursors necessary for the synthesis of RNA and DNA (1). CTPS is built up of two domains, a synthetase domain and a glutaminase domain. CTPS catalyzes the formation of CTP from UTP with the concomitant dephosphorylation of ATP and the deamination of glutamine to glutamate. The generated ammonia is transferred through a molecular tunnel to the synthetase domain (2).

ATP + UTP + NH3 => ADP + phosphate + CTP

Cancer cells that exhibit increased cell proliferation also exhibit an increased activity of CTP synthetase. Thus, CTP synthetase is an attractive target for selective chemotherapy (3). There are two isoforms of the human CTPS, CTPS1 and CTPS2, where CTPS2 is slightly smaller than CTPS and has a sequence identity of 74% (4).

Here we have determined the first eukaryotic structure of the glutaminase domain to a resolution of 2.5Å. The structure was solved with molecular replacement using the glutaminase domain of Thermus thermophilus of CTP synthetase (pdb-code: 1vco).

The structures of the full length E.coli CTPS and the synthetase domain of human CTPS (5) build up homotetramers while the glutaminase domains of E.coli CTPS are monomers (2). Despite that the glutaminase domain of CTPS2 was co-crystallized with glutamic acid there was no density for glutamic acid in the active site. The glutamine binding site is located close to the interface between the two domains. The T. thermophilus CTP synthetase with bound glutamine reveals an interaction between the glutamine and a tyrosine from the synthetase domain, which is conserved in the human CTPSs. The absence of glutamic acid in the active site might be explained by the missing interactions between the product and the conserved tyrosine.

We have also solved a follow up structure of Human CTP synthetase 2 - glutaminase domain in complex with 5-OXO-L-NORLEUCINE.

References

  1. Kent C, Carman GM. Interactions among pathways for phosphatidylcholine metabolism, CTP synthesis and secretion through the Golgi apparatus.Trends Biochem Sci. 1999 Apr;24(4):146-50.
  2. Endrizzi JA, Kim H, Anderson PM, Baldwin EP. 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. 2004 Jun 1;43(21):6447-63.
  3. Kizaki H, Williams JC, Morris HP, Weber G. Increased cytidine 5'-triphosphate synthetase activity in rat and human tumors. Cancer Res. 1980 Nov;40(11):3921-7.
  4. van Kuilenburg AB, Meinsma R, Vreken P, Waterham HR, van Gennip AH. Identification of a cDNA encoding an isoform of human CTP synthetase. Biochim Biophys Acta. 2000 Jul 24;1492(2-3):548-52.
  5. Kursula P, Flodin S, Ehn M, Hammarström M, Schüler H, Nordlund P, Stenmark P. Structure of the synthetase domain of human CTP synthetase, a target for anticancer therapy. Acta Crystallogr Sect F Struct Biol Cryst Commun. 2006 Jul 1;62(Pt 7):613-7.