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Human cytidine triphosphate synthetase (CTPS2) synthetase domain in complex with ADP

PDB Code 3IHL Target Class Nucleotide metabolism Target CTPS2 Alias CTPS2, DKFZp686C17207, FLJ43358, MGC32997 Disease Area/Function cancer Date Deposited Jul 30 2009 Authors MOCHE, M., SIPONEN, M.I., TRESAUGUES, L., ARROWSMITH, C.H., BERGLUND, H., BOUNTRA, C., COLLINS, R., EDWARDS, A.M., FLODIN, S., FLORES, A., GRASLUND, S., HAMMARSTROM, M., JOHANSSON, A., JOHANSSON, I., KARLBERG, T., KOTENYOVA, T., KOTZSCH, A., KRAGH NIELSEN, T., MARKOVA, N., NYMAN, T., PERSSON, C., ROOS, A., SAGEMARK, J., SCHUTZ P., SCHUELER, H., THORSELL, A.G., TRESAUGUES, L., VAN DEN BERG, S., WAHLBERG, E., WEIGELT, J., WELIN, M., WISNIEWSKA, M., NORDLUND, P., Structural Genomics Consortium (SGC) Related Structure 2VKT, 2V4U

About this structure

Cytidine triphosphate synthetase (CTPS; EC 6.3.4.2) catalyses the rate-limiting step in the synthesis of CTP, a key precursor of DNA, RNA and phospholipids. The enzyme consists of an N-terminal synthetase domain and a C-terminal glutaminase domain. In humans, CTPS exists as two isoforms having 74% identity at the amino-acid level (1). CTPS isoform 2 is a 586-amino-acid protein with a molecular weight of 66 kDa.

The glutaminase domain cleaves ammonium from glutamine, generating glutamate. Ammonium transfer from the glutaminase to the synthetase domain occurs either via a tunnel (2, 3) or from external ammonium (4). GTP is an allosteric activator of the holoenzyme (5) and CTP acts as a feedback inhibitor by binding to the synthetase domain (6, 7). The overall reaction catalysed by CTPS controls the intracellular CTP pool, which in turn affects the synthesis of nucleic acids. CTPS is regulated by phosphorylation by protein kinase A on several serine residues (8).

CTPS is an actively studied target for antiviral (9), antineoplastic (10) and antiparasitic (11) drug development. CTPS activity is also increased in a variety of human cancers (10, 12). Antiproliferative drugs targeted specifically towards human CTPS have been developed, with the aim of depleting cancer cells of CTP and thus slowing down tumour growth (13). Cyclopentenyl cytosine (CPEC), acivicin and 3-deazauridine are CTPS-directed drugs that slow down or arrest the proliferation of tumour cells (14-17). Resistance to some of these drugs is caused by mutations in CTPS (18).

The first crystal structures of CTPS are known from Thermus thermophilus (19) and E. coli (2), and based on these structures, together with other studies, the active site and the substrate-binding modes have been identified. Active CTPS is a homotetramer and the oligomeric state is regulated by nucleotides (20). However, experimental three-dimensional structures have not been available of CTPS from other organisms, including mammals. We have now solved the structure of the synthetase domain of human CTPS isoform 2 (3IHL) in complex with ADP and PO4 ions, the human CTPS isoform 2 glutaminase domain in its apo (2VKT) and 5-oxo-L-Norleucine inhibitor form (2V4U) and the human CTPS isoform 1 synthetase domain in complex with SO4 ions (2VO1) (19). These structures should provide a structural basis for drug development with the aim of effectively inhibiting CTPS activity in cancer cells.

References

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