Carbamoyl phosphate synthetase I

Last updated
carbamoyl-phosphate synthetase 1, mitochondrial
Identifiers
SymbolCPS1
NCBI gene 1373
HGNC 2323
OMIM 608307
RefSeq NM_001875
UniProt P31327
Other data
EC number 6.3.4.16
Locus Chr. 2 p
Search for
Structures Swiss-model
Domains InterPro

Carbamoyl phosphate synthetase I (CPS I) is a ligase enzyme located in the mitochondria involved in the production of urea. Carbamoyl phosphate synthetase I (CPS1 or CPSI) transfers an ammonia molecule to a molecule of bicarbonate that has been phosphorylated by a molecule of ATP. The resulting carbamate is then phosphorylated with another molecule of ATP. The resulting molecule of carbamoyl phosphate leaves the enzyme.

Contents

Structure

In E. coli the single CPS that carries out the functions of CPSI and CPSII is a heterodimer with a small subunit and a larger subunit with about 382 and 1073 amino acid residues in size, although in mammals (and other vertebrates) the CPSI protein is encoded by a single gene. [1] The small subunit contains one active site for the binding and deamination of glutamine to make ammonia and glutamate. The large subunit contains two active sites, one for the production of carboxyphosphate, and the other for the production of carbamoyl phosphate. [2] [3] Within the large subunit there are two domains (B and C) each with an active site of the ATP-grasp family. [1] Connecting the two subunits is a tunnel of sorts, which directs the ammonia from the small subunit to the large subunit. [4]


Mechanism

The overall reaction that occurs in CPSI is:

2ATP + HCO3− + NH4+ → 2ADP + Carbamoyl phosphate + Pi [4]

This reaction can be thought of occurring in three distinct steps. [5]

  1. Bicarbonate is phosphorylated to form carboxyphosphate
  2. Ammonia attacks the carboxyphosphate, resulting in carbamate
  3. Carbamate is phosphorylated to give carbamoyl phosphate

Regulation

CPSI is regulated by N-acetylglutamate which acts as an obligate allosteric activator of CPS1. NAG, by binding to domain L4, triggers changes in the A-loop and in Arg1453 that result in changing interactions with the T′-loop of domain L3, which reorganizes completely from a β-hairpin in the apo form to a widened loop in the ligand-bound form. In this last form, the T′-loop interacts also with the tunnel-loop and the T-loop of the L1 domain, thus transferring the activating information to the bicarbonate-phosphorylating domain. This interaction with NAG and a second interaction, with a nucleotide, stabilise the active form of CPSI. [n 1] The necessity for this ligand also connects the high concentration of nitrogen, reflected in excess of glutamate and arginine to produce NAG, to an increase in CPSI activity to clear this excess.

Metabolism

CPSI plays a vital role in protein and nitrogen metabolism. Once ammonia has been brought into the mitochondria via glutamine or glutamate, it is CPSI's job to add the ammonia to bicarbonate along with a phosphate group to form carbamoyl phosphate. Carbamoyl phosphate is then put into the urea cycle to eventually create urea. Urea can then be transferred back to the blood stream and to the kidneys for filtration and on to the bladder for excretion. [6]

The main problem related to CPSI is genetics-based. Sometimes the body does not produce enough CPSI due to a mutation in the genetic code, resulting in poor metabolism of proteins and nitrogen, as well as high levels of ammonia in the body. This is dangerous because ammonia is highly toxic to the body, especially the nervous system, and can result in intellectual disability and seizures.

Notes

  1. ↑ de Cima S, Polo LM, Díez-Fernández C, Martínez AI, Cervera J, Fita I, Rubio V (November 2015). "Structure of human carbamoyl phosphate synthetase: deciphering the on/off switch of human ureagenesis". Scientific Reports. 5 (1): 16950. Bibcode:2015NatSR...516950D. doi:10.1038/srep16950. PMC   4655335 . PMID   26592762.

Related Research Articles

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<span class="mw-page-title-main">Carbamoyl phosphate</span> Chemical compound

Carbamoyl phosphate is an anion of biochemical significance. In land-dwelling animals, it is an intermediary metabolite in nitrogen disposal through the urea cycle and the synthesis of pyrimidines. Its enzymatic counterpart, carbamoyl phosphate synthetase I, interacts with a class of molecules called sirtuins, NAD dependent protein deacetylases, and ATP to form carbamoyl phosphate. CP then enters the urea cycle in which it reacts with ornithine to form citrulline.

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<span class="mw-page-title-main">Glutamine synthetase</span> Class of enzymes

Glutamine synthetase (GS) is an enzyme that plays an essential role in the metabolism of nitrogen by catalyzing the condensation of glutamate and ammonia to form glutamine:

<i>N</i>-Acetylglutamic acid Chemical compound

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<span class="mw-page-title-main">Argininosuccinate synthase</span> Enzyme

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<i>N</i>-Acetylglutamate synthase Class of enzymes

N-Acetylglutamate synthase (NAGS) is an enzyme that catalyses the production of N-acetylglutamate (NAG) from glutamate and acetyl-CoA.

<span class="mw-page-title-main">N-Acetylglutamate synthase deficiency</span> Medical condition

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<span class="mw-page-title-main">Carbamoyl phosphate synthetase</span> Class of enzymes

Carbamoyl phosphate synthetase catalyzes the ATP-dependent synthesis of carbamoyl phosphate from glutamine or ammonia and bicarbonate. This enzyme catalyzes the reaction of ATP and bicarbonate to produce carboxy phosphate and ADP. Carboxy phosphate reacts with ammonia to give carbamic acid. In turn, carbamic acid reacts with a second ATP to give carbamoyl phosphate plus ADP.

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<span class="mw-page-title-main">GMP synthase</span>

Guanosine monophosphate synthetase, also known as GMPS is an enzyme that converts xanthosine monophosphate to guanosine monophosphate.

<span class="mw-page-title-main">Amidophosphoribosyltransferase</span> Mammalian protein found in Homo sapiens

Amidophosphoribosyltransferase (ATase), also known as glutamine phosphoribosylpyrophosphate amidotransferase (GPAT), is an enzyme responsible for catalyzing the conversion of 5-phosphoribosyl-1-pyrophosphate (PRPP) into 5-phosphoribosyl-1-amine (PRA), using the amine group from a glutamine side-chain. This is the committing step in de novo purine synthesis. In humans it is encoded by the PPAT gene. ATase is a member of the purine/pyrimidine phosphoribosyltransferase family.

<span class="mw-page-title-main">Asparagine synthetase</span> Mammalian protein found in Homo sapiens

Asparagine synthetase is a chiefly cytoplasmic enzyme that generates asparagine from aspartate. This amidation reaction is similar to that promoted by glutamine synthetase. The enzyme is ubiquitous in its distribution in mammalian organs, but basal expression is relatively low in tissues other than the exocrine pancreas.

In enzymology, an aminoacylase (EC 3.5.1.14) is an enzyme that catalyzes the chemical reaction

In enzymology, a carbamate kinase (EC 2.7.2.2) is an enzyme that catalyzes the chemical reaction

<span class="mw-page-title-main">Glutamine amidotransferase</span>

In molecular biology, glutamine amidotransferases (GATase) are enzymes which catalyse the removal of the ammonia group from a glutamine molecule and its subsequent transfer to a specific substrate, thus creating a new carbon-nitrogen group on the substrate. This activity is found in a range of biosynthetic enzymes, including glutamine amidotransferase, anthranilate synthase component II, p-aminobenzoate, and glutamine-dependent carbamoyl-transferase (CPSase). Glutamine amidotransferase (GATase) domains can occur either as single polypeptides, as in glutamine amidotransferases, or as domains in a much larger multifunctional synthase protein, such as CPSase. On the basis of sequence similarities two classes of GATase domains have been identified: class-I and class-II. Class-I GATase domains are defined by a conserved catalytic triad consisting of cysteine, histidine and glutamate. Class-I GATase domains have been found in the following enzymes: the second component of anthranilate synthase and 4-amino-4-deoxychorismate (ADC) synthase; CTP synthase; GMP synthase; glutamine-dependent carbamoyl-phosphate synthase; phosphoribosylformylglycinamidine synthase II; and the histidine amidotransferase hisH.

<span class="mw-page-title-main">Asparagine synthase (glutamine-hydrolysing)</span>

Asparagine synthase (glutamine-hydrolysing) (EC 6.3.5.4, asparagine synthetase (glutamine-hydrolysing), glutamine-dependent asparagine synthetase, asparagine synthetase B, AS, AS-B) is an enzyme with systematic name L-aspartate:L-glutamine amido-ligase (AMP-forming). This enzyme catalyses the following chemical reaction

Carbamoyl phosphate synthetase III is one of the three isoforms of the carbamoyl phosphate synthetase, an enzyme that catalyzes the active production of carbamoyl phosphate in many organisms.

References

  1. 1 2 Thoden JB, Huang X, Raushel FM, Holden HM (October 2002). "Carbamoyl-phosphate synthetase. Creation of an escape route for ammonia". The Journal of Biological Chemistry. 277 (42): 39722–7. doi: 10.1074/jbc.M206915200 . PMID   12130656.
  2. ↑ Powers SG, Griffith OW, Meister A (May 1977). "Inhibition of carbamyl phosphate synthetase by P1, P5-di(adenosine 5')-pentaphosphate: evidence for two ATP binding sites". The Journal of Biological Chemistry. 252 (10): 3558–60. doi: 10.1016/S0021-9258(17)40428-5 . PMID   193838.
  3. ↑ Thoden JB, Holden HM, Wesenberg G, Raushel FM, Rayment I (May 1997). "Structure of carbamoyl phosphate synthetase: a journey of 96 A from substrate to product". Biochemistry. 36 (21): 6305–16. doi:10.1021/bi970503q. PMID   9174345.
  4. 1 2 Kim J, Raushel FM (May 2004). "Perforation of the tunnel wall in carbamoyl phosphate synthetase derails the passage of ammonia between sequential active sites". Biochemistry. 43 (18): 5334–40. doi:10.1021/bi049945+. PMID   15122899.
  5. ↑ Meister A (1989). "Mechanism and Regulation of the Glutamine-Dependent Carbamyl Phosphate Synthetase of Escherichia Coli". Mechanism and regulation of the glutamine-dependent carbamyl phosphate synthetase of Escherichia coli. Advances in Enzymology and Related Areas of Molecular Biology. Vol. 62. pp.  315–74. doi:10.1002/9780470123089.ch7. ISBN   9780470123089. PMID   2658488.
  6. ↑ Nelson D, Cox M. Principles of Biochemistry (fourth ed.). pp. 666–669.
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