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37  structures 4054  species 1  interaction 4339  sequences 19  architectures

Family: Arginosuc_synth (PF00764)

Summary: Arginosuccinate synthase

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Argininosuccinate synthase Edit Wikipedia article

Argininosuccinate synthetase
Protein ASS1 PDB 2nz2.png
Crystallographic structure of human argininosuccinate synthetase.[1]
Identifiers
EC number 6.3.4.5
CAS number 9023-58-9
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
Argininosuccinate synthetase 1
Identifiers
Symbol ASS1
Entrez 445
HUGO 758
OMIM 603470
RefSeq NM_000050
UniProt P00966
Other data
Locus Chr. 9 q34.1
Reaction catalyzed by argininosuccinate synthetase. Adapted from Goto et al. 2003.[2]
Argininosuccinate synthetase
PDB 1j21 EBI.jpg
crystal structure of thermus thermophilus hb8 argininosuccinate synthetase in complex with atp and citrulline
Identifiers
Symbol Arginosuc_synth
Pfam PF00764
Pfam clan CL0039
InterPro IPR001518
PROSITE PDOC00488
SCOP 1kp2
SUPERFAMILY 1kp2

Argininosuccinate synthase or synthetase (ASS) (EC 6.3.4.5) is an enzyme that catalyzes the synthesis of argininosuccinate from citrulline and aspartate.

ASS is responsible for the third step of the urea cycle and one of the reactions of the citrulline-NO cycle.

Genetic structure

The gene that encodes for this enzyme, ASS, is located on chromosome 9. In humans, ASS is expressed mostly in the cells of liver and kidney. The expressed ASS gene is at least 65 kb in length, including at least 12 introns.[3]

Enzyme mechanism

In the first step of the catalyzed reaction, citrulline attacks the α-phosphate of ATP to form citrulline adenylate, a reactive intermediate. The attachment of AMP to the ureido (urea-like) group on citrulline activates the carbonyl center for subsequent nucleophilic attack. This activation facilitates the second step, in which the α-amino group of aspartate attacks the ureido group. Attack by aspartate is the rate-limiting step of the reaction. This step produces free AMP and L-argininosuccinate.[4]

Thermodynamically, adenylation of the citrulline ureido group is more favorable than the analogous phosphorylation. Additionally, attack by citrulline at the α-phosphate of ATP produces an equivalent of pyrophosphate, which can be hydrolyzed in a thermodynamically favorable reaction to provide additional energy to drive the adenylation.[5]

Enzyme structure

Quaternary structure

Argininosuccinate synthetase is a homotetramer, with each subunit consisting of 412 residues.[6] The interfaces between subunits contain a number of salt bridges and hydrogen bonds, and the C-terminus of each subunit is involved in oligomerization by interacting with the C-termini and nucleotide-binding domains of the other subunits.[7]

Active site

X-ray crystal structures have been generated for argininosuccinate synthetase from Thermus thermophilus, E. coli, Thermotoga maritime, and Homo sapiens. In ASS from T. thermophilus, E. coli, and H. sapiens, citrulline and aspartate are tightly bound in the active site by interactions with serine and arginine residues; interactions of the substrates with other residues in the active site vary by species. In T. thermophilus, the ureido group of citrulline appears to be repositioned during nucleophilic attack to attain sufficient proximity to the α-phosphate of ATP.[2] In E. coli, it is suggested that binding of ATP causes a conformational shift that brings together the nucleotide-binding domain and the synthetase domain.[8] An argininosuccinate synthetase structure with a bound ATP in the active site has not been attained, although modeling suggests that the distance between ATP and the ureido group of citrulline is smaller in human argininosuccinate synthetase than in the E. coli variety, so it is likely that a much smaller conformational change is necessary for catalysis.[7] The ATP binding domain of argininosuccinate synthetase is similar to that of other N-type ATP pyrophosphatases.[8]

Active site of argininosuccinate synthetase shown with bound citrulline, ATP, and aspartate interacting with select active site residues. Modeled using PyMol from PDB 1J1Z.

Biological function

Argininosuccinate synthetase is involved in the synthesis of creatine, polyamines, arginine, urea, and nitric oxide.[9]

Arginine synthesis

The transformation of citrulline into argininosuccinate is the rate-limiting step in arginine synthesis. The activity of argininosuccinate synthetase in arginine synthesis occurs largely in at the outer mitochondrial membrane of periportal liver cells as part of the urea cycle, with some activity occurring in cortical kidney cells.[6][9] Genetic defects that cause incorrect localization of argininosuccinate synthetase to the outer mitochondrial membrane cause type II citrullinemia.[9]

In fetuses and infants, arginine is also produced via argininosuccinate synthetase activity in intestinal cells, presumably to supplement the low level of arginine found in mother’s milk. Expression of argininosuccinate synthetase in the intestines ceases after two to three years of life.[9]

It is thought that regulation of argininosuccinate synthetase activity in arginine synthesis occurs primarily at the transcriptional level in response to glucocorticoids, cAMP, glucagon, and insulin.[10] It has also been demonstrated in vitro that arginine down-regulates argininosuccinate synthetase expression, while citrulline up-regulates it.[9]

Citrulline-NO cycle

The enzyme endothelial nitric oxide synthase produces nitric oxide from arginine in endothelial cells.[9] Argininosuccinate synthetase and argininosuccinate lyase recycle citrulline, a byproduct of nitric oxide production, into arginine. Since nitric oxide is an important signaling molecule, this role of ASS is important to vascular physiology. In this role, argininosuccinate synthetase activity is regulated largely by inflammatory cellular signal molecules such as cytokines.[6]

In endothelial cells, it has been shown that ASS expression is increased by laminar shear stress due to pulsative blood flow.[11] Emerging evidence suggests that ASS may also be subject to regulation by phosphorylation at the Ser-328 residue by protein kinase C[12] and by nitrosylation at the Cys-132 residue by nitric oxide synthase.[7]

Role in disease

Citrullinemia

Citrullinemia is an inherited autosomal recessive disease.[13] At least 50 mutations that cause type I citrullinemia have been identified in the ASS gene. Most of these mutations substitute one amino acid for another in ASS. These mutations likely affect the structure of the enzyme and its ability to bind to citrulline, aspartate, and other molecules. A few mutations lead to the production of an abnormally short enzyme that cannot effectively play its role in the urea cycle.

Defects in ASS disrupt the third step of the urea cycle, preventing the liver from processing excess nitrogen into urea. As a result, nitrogen (in the form of ammonia) and other byproducts of the urea cycle (such as citrulline) build up in the bloodstream. Ammonia is toxic, particularly to the nervous system. An accumulation of ammonia during the first few days of life leads to poor feeding, vomiting, seizures, and the other signs and symptoms of type I citrullinemia.

Treatment for this defect includes a low-protein diet and dietary supplementation with arginine and phenylacetate. Arginine allows the urea cycle to complete itself, creating the substrates needed to originally fix ammonia. This will lower blood pH. Additionally, phenylacetate reacts with backed-up glutamine, resulting on phenylacetoglutamine, which can be excreted renally.[14]

Cancer biochemistry

A lack of argininosuccinate synthetase expression has been observed in several types of cancer cells, including pancreatic cancer, liver cancer,[15] and melanoma.[16] For example, defects in ASS have been seen in 87% of pancreatic cancers. Cancer cells are therefore unable to synthesize enough arginine for cellular processes and so must rely on dietary arginine. Depletion of plasma arginine using arginine deiminase has been shown to lead to regression of tumours in mice.[17]

See also

References

  1. ^ PDB 2nz2; Karlberg T, Collins R, van den Berg S, Flores A, Hammarström M, Högbom M, Holmberg Schiavone L, Uppenberg J (March 2008). "Structure of human argininosuccinate synthetase". Acta Crystallogr. D Biol. Crystallogr. 64 (Pt 3): 279–86. doi:10.1107/S0907444907067455. PMID 18323623. 
  2. ^ a b Goto M, Omi R, Miyahara I, Sugahara M, Hirotsu K (June 2003). "Structures of argininosuccinate synthetase in enzyme-ATP substrates and enzyme-AMP product forms: stereochemistry of the catalytic reaction". J. Biol. Chem. 278 (25): 22964–71. doi:10.1074/jbc.M213198200. PMID 12684518. 
  3. ^ Freytag SO, Beaudet AL, Bock HG, O'Brien WE (October 1984). "Molecular structure of the human argininosuccinate synthetase gene: occurrence of alternative mRNA splicing". Mol. Cell. Biol. 4 (10): 1978–84. PMC 369014. PMID 6095035. 
  4. ^ Ghose C, Raushel FM (October 1985). "Determination of the mechanism of the argininosuccinate synthetase reaction by static and dynamic quench experiments". Biochemistry 24 (21): 5894–8. doi:10.1021/bi00342a031. PMID 3878725. 
  5. ^ Kumar S, Lennane J, Ratner S (October 1985). "Argininosuccinate synthetase: essential role of cysteine and arginine residues in relation to structure and mechanism of ATP activation". Proc. Natl. Acad. Sci. U.S.A. 82 (20): 6745–9. doi:10.1073/pnas.82.20.6745. PMC 390763. PMID 3863125. 
  6. ^ a b c Husson A, Brasse-Lagnel C, Fairand A, Renouf S, Lavoinne A (May 2003). "Argininosuccinate synthetase from the urea cycle to the citrulline-NO cycle". Eur. J. Biochem. 270 (9): 1887–99. doi:10.1046/j.1432-1033.2003.03559.x. PMID 12709047. 
  7. ^ a b c Karlberg T, Collins R, van den Berg S, Flores A, Hammarström M, Högbom M, Holmberg Schiavone L, Uppenberg J (March 2008). "Structure of human argininosuccinate synthetase". Acta Crystallogr. D Biol. Crystallogr. 64 (Pt 3): 279–86. doi:10.1107/S0907444907067455. PMID 18323623. 
  8. ^ a b Lemke CT, Howell PL (December 2001). "The 1.6 A crystal structure of E. coli argininosuccinate synthetase suggests a conformational change during catalysis". Structure 9 (12): 1153–64. doi:10.1016/S0969-2126(01)00683-9. PMID 11738042. 
  9. ^ a b c d e f Haines RJ, Pendleton LC, Eichler DC (2011). "Argininosuccinate synthase: at the center of arginine metabolism". Int J Biochem Mol Biol 2 (1): 8–23. PMC 3074183. PMID 21494411. 
  10. ^ Morris SM (2002). "Regulation of enzymes of the urea cycle and arginine metabolism". Annu. Rev. Nutr. 22: 87–105. doi:10.1146/annurev.nutr.22.110801.140547. PMID 12055339. 
  11. ^ Mun GI, Boo YC (April 2012). "A regulatory role of Kruppel-like factor 4 in endothelial argininosuccinate synthetase 1 expression in response to laminar shear stress". Biochem. Biophys. Res. Commun. 420 (2): 450–5. doi:10.1016/j.bbrc.2012.03.016. PMID 22430140. 
  12. ^ Haines RJ, Corbin KD, Pendleton LC, Eichler DC (July 2012). "Protein kinase Cα phosphorylates a novel argininosuccinate synthase site at serine 328 during calcium-dependent stimulation of endothelial nitric-oxide synthase in vascular endothelial cells". J. Biol. Chem. 287 (31): 26168–76. doi:10.1074/jbc.M112.378794. PMC 3406701. PMID 22696221. 
  13. ^ Häberle J, Pauli S, Linnebank M, Kleijer WJ, Bakker HD, Wanders RJ, Harms E, Koch HG (April 2002). "Structure of the human argininosuccinate synthetase gene and an improved system for molecular diagnostics in patients with classical and mild citrullinemia". Hum. Genet. 110 (4): 327–33. doi:10.1007/s00439-002-0686-6. PMID 11941481. 
  14. ^ Devlin TM (2002). Textbook of biochemistry: with clinical correlations. New York: Wiley-Liss. p. 788. ISBN 0-471-41136-1. 
  15. ^ Wu L, Li L, Meng S, Qi R, Mao Z, Lin M (February 2013). "Expression of argininosuccinate synthetase in patients with hepatocellular carcinoma". J. Gastroenterol. Hepatol. 28 (2): 365–8. doi:10.1111/jgh.12043. PMID 23339388. 
  16. ^ Yoon JK, Frankel AE, Feun LG, Ekmekcioglu S, Kim KB (2013). "Arginine deprivation therapy for malignant melanoma". Clin Pharmacol 5: 11–9. doi:10.2147/CPAA.S37350. PMC 3534294. PMID 23293541. 
  17. ^ Bowles TL, Kim R, Galante J, Parsons CM, Virudachalam S, Kung HJ, Bold RJ (October 2008). "Pancreatic cancer cell lines deficient in argininosuccinate synthetase are sensitive to arginine deprivation by arginine deiminase". Int. J. Cancer 123 (8): 1950–5. doi:10.1002/ijc.23723. PMID 18661517. 

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Arginosuccinate synthase Provide feedback

This family contains a PP-loop motif [1].

Literature references

  1. Bork P, Koonin EV; , Proteins 1994;20:347-355.: A P-loop-like motif in a widespread ATP pyrophosphatase domain: implications for the evolution of sequence motifs and enzyme activity. PUBMED:7731953 EPMC:7731953


External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR001518

Argininosuccinate synthase (EC) (AS) is a urea cycle enzyme that catalyzes the penultimate step in arginine biosynthesis: the ATP-dependent ligation of citrulline to aspartate to form argininosuccinate, AMP and pyrophosphate [PUBMED:2123815, PUBMED:3133361].

In humans, a defect in the AS gene causes citrullinemia, a genetic disease characterised by severe vomiting spells and mental retardation.

AS is a homotetrameric enzyme of chains of about 400 amino-acid residues. An arginine seems to be important for the enzyme's catalytic mechanism. The sequences of AS from various prokaryotes, archaebacteria and eukaryotes show significant similarity.

Gene Ontology

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Domain organisation

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Pfam Clan

This family is a member of clan HUP (CL0039), which has the following description:

The HUP class contains the HIGH-signature proteins, UspA superfamily and the PP-ATPase superfamily [1]. The HIGH superfamily has the HIGH Nucleotidyl transferases and the class I tRNA synthetases both of which have the HIGH and the KMSKS motif [1],[2]. The PP-loop ATPase named after the ATP PyroPhosphatase domain, was initially identified as a conserved amino acid sequence motif in four distinct groups of enzymes that catalyse the hydrolysis of the alpha-beta phosphate bond of ATP, namely GMP synthetases, argininosuccinate synthetases, asparagine synthetases, and ATP sulfurylases [3]. The USPA superfamily contains USPA, ETFP and Photolyases [1]

The clan contains the following 26 members:

Arginosuc_synth Asn_synthase ATP-sulfurylase ATP_bind_3 ATP_bind_4 Citrate_ly_lig CTP_transf_2 DNA_photolyase ETF FAD_syn HIGH_NTase1 NAD_synthase Pantoate_ligase PAPS_reduct QueC ThiI tRNA-synt_1 tRNA-synt_1_2 tRNA-synt_1b tRNA-synt_1c tRNA-synt_1d tRNA-synt_1e tRNA-synt_1f tRNA-synt_1g tRNA_Me_trans Usp

Alignments

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RP75
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  Seed
(12)
Full
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(3498)
Meta
(3319)
RP15
(359)
RP35
(740)
RP55
(981)
RP75
(1169)
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Curation and family details

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Seed source: Pfam-B_888 (release 2.1)
Previous IDs: none
Type: Family
Author: Bateman A
Number in seed: 12
Number in full: 4339
Average length of the domain: 374.20 aa
Average identity of full alignment: 40 %
Average coverage of the sequence by the domain: 92.38 %

HMM information View help on HMM parameters

HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 21.0 21.0
Trusted cut-off 21.0 21.0
Noise cut-off 20.9 20.9
Model length: 388
Family (HMM) version: 14
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Species distribution

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Interactions

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Arginosuc_synth

Structures

For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the Arginosuc_synth domain has been found. There are 37 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.

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