Amidophosphoribosyltransferase
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Location (UCSC) | Chr 4: 56.39 – 56.44 Mb | Chr 5: 77.06 – 77.1 Mb | |||||||
PubMed search | [3] | [4] |
View/Edit Human | View/Edit Mouse |
Amidophosphoribosyltransferase (ATase), also known as glutamine phosphoribosylpyrophosphate amidotransferase (GPAT), is an
Structure and function
amidophosphoribosyltransferase | |||||||||
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ExPASy | NiceZyme view | ||||||||
KEGG | KEGG entry | ||||||||
MetaCyc | metabolic pathway | ||||||||
PRIAM | profile | ||||||||
PDB structures | RCSB PDB PDBe PDBsum | ||||||||
Gene Ontology | AmiGO / QuickGO | ||||||||
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The enzyme consists of two domains: a glutaminase domain that produces ammonia from glutamine by hydrolysis and a phosphoribosyltransferase domain that binds the ammonia to ribose-5-phosphate.[7] Coordination between the two active sites of enzyme give it special complexity.
The glutaminase domain is homologous to other N-terminal nucleophile (Ntn)
The PRTase domain is homologous to many other PRTases involved in the purine nucleotide synthesis and salvage pathways. All PRTases involve the displacement of pyrophosphate in PRPP by a variety of nucleophiles.[10] ATase is the only PRTase that has ammonia as a nucleophile.[7] Pyrophosphate from PRPP is an excellent leaving group, so little chemical assistance is needed to promote catalysis. Rather, the primary function of the enzyme appears to be bringing the reactants together appropriately and preventing the wrong reaction, such as hydrolysis.[7]
Besides having their respective catalytic abilities, the two domains also coordinate with one another to ensure that all the ammonia produced from glutamine is transferred to PRPP and no other nucleophile than ammonia attacks PRPP. This is achieved mainly by blocking formation of ammonia until PRPP is bound and channelling the ammonia to the PRTase active site.[7]
Initial activation of the enzyme by PRPP is caused by a conformational change in a "glutamine loop", which repositions to be able to accept glutamine. This results in a 200-fold higher Km value for glutamine binding[11] Once glutamine has bound to the active site, further conformational changes bring the site into the enzyme, making it inaccessible.[7]
These conformational changes also result in the formation of a 20 Å long ammonia channel, one of the most striking features of this enzyme. This channel lacks any hydrogen bonding sites, to ensure easy diffusion of ammonia from one active site to the other. This channel ensures ammonia released from glutamine reaches the PRTase catalytic site, and it differs from the channel in CPSase[12] in that it is hydrophobic rather than polar, and transient rather than permanent.[7]
Reaction mechanism
The overall reaction catalyzed by ATase is the following:
- PRPP + glutamine → PRA + glutamate + PPi
Within the enzyme, the reaction is broken down into two half-reactions that occur at different active sites:
- glutamine → NH
3 + glutamate - PRPP + NH
3 → PRA + PPi
The first part of the mechanism occurs in the active site of the glutaminase domain and releases an ammonia group from glutamine by hydrolysis. The ammonia released by the first reaction is then transferred to the active site of the phosphoribosyltransferase domain via a 20 Å channel, where it then binds to PRPP to form PRA.
Regulation
In an example of
Due to the chemical lability of PRA, which has a half-life of 38 seconds at pH 7.5 and 37 °C, researchers have suggested that the compound is channeled from Amidophosphoribosyltransferase to GAR synthetase in vivo.[15]
Interactive pathway map
Click on genes, proteins and metabolites below to link to respective articles.[§ 1]
- ^ The interactive pathway map can be edited at WikiPathways: "FluoropyrimidineActivity_WP1601".
Gallery
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PRPP
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5-phosphoribosylamine
References
- ^ a b c GRCh38: Ensembl release 89: ENSG00000128059 – Ensembl, May 2017
- ^ a b c GRCm38: Ensembl release 89: ENSMUSG00000029246 – Ensembl, May 2017
- ^ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
- ^ "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
- ^ "Entrez Gene: phosphoribosyl pyrophosphate amidotransferase".
- PMID 8106516.
- ^ PMID 9914248.
- PMID 8197456.
- ^ "Overview for MACiE Entry M0214". EMBL-EBI. Archived from the original on 2015-04-02. Retrieved 2015-03-10.
- PMID 7030616.
- PMID 8663035.
- PMID 9174345.
- PMID 9271502.
- PMID 8120039.
- PMID 8626510.
Further reading
- Iwahana H, Oka J, Mizusawa N, Kudo E, Ii S, Yoshimoto K, Holmes EW, Itakura M (Jan 1993). "Molecular cloning of human amidophosphoribosyltransferase". Biochemical and Biophysical Research Communications. 190 (1): 192–200. PMID 8380692.
- Gassmann MG, Stanzel A, Werner S (Nov 1999). "Growth factor-regulated expression of enzymes involved in nucleotide biosynthesis: a novel mechanism of growth factor action". Oncogene. 18 (48): 6667–76. PMID 10597272.
- Chen S, Nagy PL, Zalkin H (May 1997). "Role of NRF-1 in bidirectional transcription of the human GPAT-AIRC purine biosynthesis locus". Nucleic Acids Research. 25 (9): 1809–16. PMID 9108165.
- Stanley W, Chu EH (1978). "Assignment of the gene for phosphoribosylpyrophosphate amidotransferase to the pter leads to q21 region of human chromosome 4". Cytogenetics and Cell Genetics. 22 (1–6): 228–31. PMID 752480.
- Maruyama K, Sugano S (Jan 1994). "Oligo-capping: a simple method to replace the cap structure of eukaryotic mRNAs with oligoribonucleotides". Gene. 138 (1–2): 171–4. PMID 8125298.
- Bera AK, Chen S, Smith JL, Zalkin H (Dec 1999). "Interdomain signaling in glutamine phosphoribosylpyrophosphate amidotransferase". The Journal of Biological Chemistry. 274 (51): 36498–504. PMID 10593947.
- Zalkin H, Dixon JE (1992). De novo purine nucleotide biosynthesis. Vol. 42. pp. 259–87. )
- Suzuki Y, Yoshitomo-Nakagawa K, Maruyama K, Suyama A, Sugano S (Oct 1997). "Construction and characterization of a full length-enriched and a 5'-end-enriched cDNA library". Gene. 200 (1–2): 149–56. PMID 9373149.
External links
- Amidophosphoribosyl transferase at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- Human PPAT genome location and PPAT gene details page in the UCSC Genome Browser.
This article incorporates text from the United States National Library of Medicine, which is in the public domain.