CTP synthase

CTP synthase
Cytidine triphosphate
Identifiers
EC number	6.3.4.2
CAS number	9023-56-7
Databases
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	profile
PDB structures	RCSB PDB PDBe PDBsum
Gene Ontology	AmiGO / EGO
Search PMC articles PubMed articles

CTP synthase (or CTP synthetase) is an enzyme involved in pyrimidine biosynthesis that interconverts UTP and CTP.^[1][2]

Enzyme Structure

Dimeric form of CTP synthase from Sulfolobus solfataricus (PDB code: 3NVA). Chain A is depicted in blue and Chain B in green.

Active CTP synthase exists as a homeotetrameric enzyme. At low enzyme concentrations and in the absence of ATP and UTP, CTP synthase exists as inactive monomer. As enzyme concentration increases, it polymerizes first to a dimer (such as the form shown to the left) and, in the presence of ATP and UTP, forms a tetramer.^[3][4]

The enzyme contains two major domains, responsible for the aminotransferase and synthase activity, respectively. The amidotransferase domains are located away from the tetramer interfaces and are not affected by the oligomeric state. The ATP-binding site and CTP-binding site in the synthase domain are located at the tetramer interface. It is for this reason that ATP and UTP are required for tertamerization.^[5]

Two isozymes with CTP synthase activity exist in humans, encoded by the following genes:

• CTPS – CTP synthase 1
• CTPS2 – CTP synthase 2

Enzyme Mechanism

CTP synthase catalyzes the last committed step in pyrimidine nucleotide biosynthesis:^[6]

ATP + UTP + glutamine --> ADP + Pi + CTP + glutamate

It is the rate-limiting enzyme for the synthesis of cytosine nucleotides from both the de novo and uridine salvage pathways.^[7]

The reaction proceeds by the ATP-dependent phosphorylation of UTP on the 4-oxygen atom, making the 4-carbon electrophilic and vulnerable to reaction with ammonia.^[3] The source of the amino group in CTP is glutamine, which is hydrolysed in a glutamine amidotransferase domain to produce ammonia. This is then channeled through the interior of the enzyme to the synthase domain.^[8][9] Here, ammonia reacts with the intermediate 4-phosphoryl UTP.^[10]

Regulation

CTP synthase is precisely regulated by the intracellular concentrations of CTP and UPT, and both hCTPS1 and hCTPS2 have been seen to be maximally active at physiological concentrations of ATP, GTP, and glutamine.^[11]

The activity of human CTPS1 isozyme has been demonstrated to be inhibited by phosphorylation.^[12] One major example of this is phosphorylation of the Ser-571 residue by glycogen synthase kinase 3 (GSK3) in response to low serum conditions.^[13] Additionally, Ser568 has been seen to be phosphorylated by casein kinase 1, inhibiting CTP synthase activity.^[11]

CTP is also subject to various froms of allosteric regulation. GTP acts as an allosteric activator that strongly promotes the hydrolysis of glutamine, but is also inhibiting to glutamine-dependent CTP formation at high concentrations.^[14] This acts to balance the relative amounts of purine and pyrimidine nucleotides. The reaction product CTP also serves as an allosteric inhibitor. The triphosphate binding site overlaps with that of UTP, but the nucleoside moiety of CTP binds in an alternative pocket opposite the binding site for UTP.^[15]

The glutamine analog DON has also been seen to act as an irreversible inhibitor, and has been used as an anti-cancer agent.^[16]

Cytoophidium

The cytoophidium (Greek: cyto-, meaning cell, and ophidium, meaning serpent) is a snake-like filamentary structure containing CTP synthase, first reported in the fruit flies (D. melanogaster, D. virilis and D. peudoobscura).^[17] CTP synthase-containing filaments (i.e., cytoophidium) have also been found in bacteria including C. crescentus and E. coli,^[18] indicating that the cytoophidium is well conserved from prokaryotes to eukaryotes.^{[citation needed]}

Disease Relevance

Upregulated CTP synthase activity has been widely seen in human and rodent tumors.^[19]

Mutations in the CTP synthase have been seen to confer resistance to cytotoxic drugs such as cytosine arabinoside (ara-C) in a Chinese hamster ovary (CHO) cell model of leukemia though such mutations were not found in human patients with ara-C resistance.^[20]

See also

• pyrimidine biosynthesis

References

1. ^ Lieberman, Irving (1956). "Enzymatic amination of uridine triphosphate to cytidine triphosphate". The Journal of Biological Chemistry 222 (2): 765–75. PMID 13367044. http://www.jbc.org/cgi/pmidlookup?view=long&pmid=13367044. 
2. ^ Long, Cedric W.; Levitzki, Alexander; Koshland, D. E. (1970). "The subunit structure and subunit interactions of cytidine triphosphate synthetase". The Journal of Biological Chemistry 245 (1): 80–7. PMID 5411547. http://www.jbc.org/cgi/pmidlookup?view=long&pmid=5411547. 
3. ^ ^{a b} von der Saal, Wolfgang; Anderson, Paul M.; Villafranca, Joseph J. (1985). "Mechanistic investigations of Escherichia coli cytidine-5'-triphosphate synthetase. Detection of an intermediate by positional isotope exchange experiments". The Journal of Biological Chemistry 260 (28): 14993–7. PMID 2933396. http://www.jbc.org/cgi/pmidlookup?view=long&pmid=2933396. 
4. ^ Anderson, Paul M. (1983). "CTP synthetase from Escherichia coli: an improved purification procedure and characterization of hysteretic and enzyme concentration effects on kinetic properties". Biochemistry 22 (13): 3285–92. doi:10.1021/bi00282a038. PMID 6349684. 
5. ^ Lauritsen, Iben; Willemoës, Martin; Jensen, Kaj Frank; Johansson, Eva; Harris, Pernille (2011). "Structure of the dimeric form of CTP synthase fromSulfolobus solfataricus". Acta Crystallographica F 67 (2): 201–8. doi:10.1107/S1744309110052334. PMC 3034608. PMID 21301086. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3034608. 
6. ^ Koshland, D. E.; Levitzki, A. (1974). "CTP Synthetase and Related Enzymes". In Boyer, Paul D. The Enzymes (3rd ed.). New York: Academic Press. pp. 539–59. ISBN 978-0-12-122710-4. http://books.google.com/books?id=9Jz_CZs5lFgC&pg=PA539. 
7. ^ van Kuilenburg, AB; Meinsma, R; Vreken, P; Waterham, HR; van Gennip, AH (2000). "Isoforms of human CTP synthetase". Adv Exp Med Biol 486: 257–61. PMID 11783495. 
8. ^ Levitzki, A; Koshland, DE (1971). "Cytidine triphosphate synthetase. Covalent intermediates and mechanisms of action.". Biochemistry 10 (18): 3365–71. doi:10.1021/bi00794a008. PMID 4940761. 
9. ^ Endrizzi, James A.; Kim, Hanseong; Anderson, Paul M.; Baldwin, Enoch P. (2004). "Crystal Structure ofEscherichia coli Cytidine Triphosphate Synthetase, a Nucleotide-Regulated Glutamine Amidotransferase/ATP-Dependent Amidoligase Fusion Protein and Homologue of Anticancer and Antiparasitic Drug Targets". Biochemistry 43 (21): 6447–63. doi:10.1021/bi0496945. PMC 2891762. PMID 15157079. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2891762. 
10. ^ Lewis, Deborah A.; Villafranca, Joseph J. (1989). "Investigation of the mechanism of CTP synthetase using rapid quench and isotope partitioning methods". Biochemistry 28 (21): 8454–9. doi:10.1021/bi00447a027. PMID 2532543. 
11. ^ ^{a b} Kassel, K. M.; Au da R; Higgins, M. J.; Hines n, M.; Graves, L. M. (2010). "Regulation of human cytidine triphosphate synthetase 2 by phosphorylation.". J Biol Chem 285 (44): 33727–36. doi:10.1074/jbc.M110.178566. PMID 20739275. 
12. ^ Carman, GM; Kersting, MC (2004). "Phospholipid synthesis in yeast: regulation by phosphorylation.". Biochem Cell Biol 82 (1): 62–70. doi:10.1139/o03-064. PMID 15052328. 
13. ^ Higgins, ML; Graves, PR; Graves, LM (2007). "Regulation of human cytidine triphosphate synthetase 1 by glycogen synthase kinase 3.". J Biol Chem 282 (40): 29493–503. doi:10.1074/jbc.M703948200. PMID 17681942. 
14. ^ Lunn, FA; MacDonnell, JE; Bearne, SL (2007). "Structural requirements for the activation of Escherichia coli CTP synthase by the allosteric effector GTP are stringent, but requirements for inhibition are lax". J Biol Chem 283 (4): 2010–20. doi:10.1074/jbc.M707803200. PMID 18003612. 
15. ^ Endrizzi, J; Kim, H; Anderson, PM; Baldwin, EP (2005). "Mechanisms of product feedback regulation and drug resistance in cytidine triphosphate synthetases from the structure of a CTP-inhibited complex". Biochemistry 44 (41): 13491–9. doi:10.1021/bi051282o. PMC 2891682. PMID 16216072. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2891682. 
16. ^ Ahluwalia, Gurpreet S.; Grem, Jean L.; Hao, Zhang; Cooney, David A. (1990). "Metabolism and action of amino acid analog anti-cancer agents". Pharmacology & Therapeutics 46 (2): 243–71. doi:10.1016/0163-7258(90)90094-I. PMID 2108451. 
17. ^ Liu, Ji-Long (2010). "Intracellular compartmentation of CTP synthase in Drosophila". Journal of Genetics and Genomics 37 (5): 281–96. doi:10.1016/S1673-8527(09)60046-1. PMID 20513629. 
18. ^ Ingerson-Mahar, Michael; Briegel, Ariane; Werner, John N.; Jensen, Grant J.; Gitai, Zemer (2010). "The metabolic enzyme CTP synthase forms cytoskeletal filaments". Nature Cell Biology 12 (8): 739–46. doi:10.1038/ncb2087. PMID 20639870. 
19. ^ Kizaki, Harutoshi; Williams, Jim C.; Morris, Harold P.; Weber, George (1980). "Increased cytidine 5'-triphosphate synthetase activity in rat and human tumors". Cancer research 40 (11): 3921–7. PMID 7471043. http://cancerres.aacrjournals.org/cgi/pmidlookup?view=long&pmid=7471043. 
20. ^ Whelan, J; Smith, T; Phear, G; Rohatiner, A; Lister, A; Meuth, M (1994). "Resistance to cytosine arabinoside in acute leukemia: the significance of mutations in CTP synthetase". Leukemia 8 (2): 264–5. PMID 8309250. 

External links

• MeSH CTP+synthetase

This enzyme-related article is a stub. You can help Wikipedia by expanding it.v · Categories: Enzymes Enzyme stubs Wikimedia Foundation. 2010. Игры ⚽ Нужна курсовая? Edward Faulks Aircraft finance Look at other dictionaries: CTP synthase — CTP syn·thase (sinґthās) [EC 6.3.4.2] an enzyme of the transferase class that catalyzes the transfer of an amino group to UTP to form CTP, using glutamine or ammonia as a donor. The reaction is part of pyrimidine nucleotide biosynthesis …   Medical dictionary CTPS2 — CTP synthase II, also known as CTPS2, is a human gene.cite web | title = Entrez Gene: CTPS2 CTP synthase II| url = http://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene Cmd=ShowDetailView TermToSearch=56474| accessdate = ] PBB Summary section title =… …   Wikipedia Metabolism — Cell metabolism redirects here. For the journal, see Cell Metabolism. Structure of adenosine triphosphate, a central intermediate in energy metabolism Metabolism (from Greek: μεταβολή metabolē , change or Greek: μεταβολισμός metabolismos,… …   Wikipedia List of EC numbers (EC 6) — This list contains a list of EC numbers for the sixth group, EC 6, ligases, placed in numerical order as determined by the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology.EC 6.1: Forming Carbon Oxygen… …   Wikipedia Uridine monophosphate synthetase — PDB rendering based on 2eaw …   Wikipedia Dihydroorotate dehydrogenase — Dihydroorotate oxidase Identifiers EC number 1.3.3.1 CAS number 9029 03 2 …   Wikipedia Dihydrofolate reductase — Ribbon diagram of human dihydrofolate reductase in complex with folate (blue). From PDB 1DRF …   Wikipedia Purine nucleoside phosphorylase — Not to be confused with polynucleotide phosphorylase. purine nucleoside phosphorylase Identifiers EC number 2.4.2.1 CAS number …   Wikipedia Cytidine triphosphate — IUPAC name [(2R,3S,4R,5R) 5 (4 amino 2 oxopyrimidin 1 yl) 3,4 dihydroxyoxolan 2 yl]methyl(hydroxy phosphon …   Wikipedia Orotidine 5'-phosphate decarboxylase — E. coli OMP decarboxylase.[1] Identifiers EC number …   Wikipedia 18+ © Academic, 2000-2024 Contact us: Technical Support, Advertising Dictionaries export, created on PHP, Joomla, Drupal, WordPress, MODx. Mark and share Search through all dictionaries Translate… Search Internet Share the article and excerpts Direct link … Do a right-click on the link above and select “Copy Link”