Cofactors

There are no Cofactors for this Enzyme

Reaction Mechanism

amidophosphoribosyltransferase By Reference

Glutamine phosphoribosylpyrophosphate amido transferase (GPATase) catalyses the transfer of the glutamine amide nitrogen to phosphoribosylpyrophosphate to generate phosphoribosylamine, pyrophosphate and glutamate. The enzyme is a member of a family of proteins which utilise the amide nitrogen of glutamate for the biosynthesis of amino acids, nucleotides, amino sugars and coenzymes. The coupling of phosphoribosyl transferase and glutaminase actities in an enzyme is not frequently seen but required for de novo purine synthesis.




• Summary
• Step 1
• Step 2
• Step 3
• Step 4
• Step 5
• Products

The enzyme is described as complex; its reaction is catyalysed as two half reactions, each occurring at separate catalytic sites along a single polypeptide chain. The two sites are highly coupled, facilitating the transfer of NH3 between them. The N terminal domain is a member of the Ntn hydrolase family and catalyses the hydrolysis of glutamine to glutamate and ammonia, while the C terminal domain, the ammonia acceptor domain, a member of the phophoribosyltransferase (PRTase) family is responsible for the coupling of ammonia to phosphoribosyl pyrophosphate (PRPP). The PRTase active site is described as non classical, since no catalytic residues have been identified. However, it has been suggested by analogy with a homologue mechanism that the main function of the enzyme is not to promote catalysis, but rather to bring the reactants together appropriately and preventing unwanted side reactions.

Catalytic Residues

AA	Uniprot	Uniprot Resid	PDB	PDB Resid
Cys	P0AG16	2	1ecf	1
Gly	P0AG16	103	1ecf	102
Asn	P0AG16	102	1ecf	101
Cys	P0AG16	2	1ecf	1
Gly	P0AG16	28	1ecf	27
Tyr	P0AG16	259	1ecf	258

Step Components

intermediate formation, intermediate terminated, native state of enzyme regenerated, overall reactant used, dephosphorylation, bimolecular nucleophilic addition, unimolecular elimination by the conjugate base, proton relay, bimolecular nucleophilic substitution, enzyme-substrate complex formation, enzyme-substrate complex cleavage, deamination, intermediate collapse, proton transfer, overall product formed



Step 1.

Reaction occurs in the glutaminase domain (CATH code 3.60.20.10). The glutamine will only bind if the 5-phospho-alpha-D-ribose-1-diphosphate is bound first [PMID:9914248]. The N-terminus of Cys1 deprotonates the thiol group of Cys1, which attacks the amino carbon in a nucleophilic addition.



Step 2.

The oxyanion initiates an elimination that cleaves ammonia from the bound L-Glutamine substrate. Ammonia deprotonates the N-terminus of Cys1. The ammonia formed here goes onto the next domain via an intramolecular channel.



Step 3.

The N-terminus of Cys1 deprotonates water, which attacks the carbonyl carbon of the covalently bound intermediate.



Step 4.

The oxyanion initiates an elimination that cleaves the C-S bond, the thiolate of Cys1 deprotonates the N-terminus of Cys1



Step 5.

Reaction occurs in the PRTase Domain. The conformation of the enzyme-bound Mn-cPRPP for catalysis as it favours the formation of a tri- or pentavalent intermediate with some double bond character in the ribose C1-O4 bond. . The step is described as an in-line displacement in which ammonia attacks the C1 of the 5-Phospho-alpha-D-ribose-1-diphosphate substrate in a nucleophilic substitution. The product pyrophosphate deprotonates the newly attached ammonia. However, it is unclear whether the intermediate is actually a transition state. There are no residues that are essential for catalytic activity, however the Tyr258 is probably stabilising [PMID:9914248].



Products.

The products of the reaction.

View Reaction Mechanisms in M-CSA

Reaction Parameters

• Kinetic Parameters

  Organism	KM Value [mM]	Substrate	Comment
  Homo sapiens	0.65	Mg2+
  Escherichia coli	7.34	NH3
  Glycine max	16	NH3
  Columba livia	0.1	L-glutamine
  Rattus norvegicus	0.53	L-glutamine

  View all in Brenda
• Temperature

  There are no reaction parameters information for this Enzyme.

• pH

  Organism	pH Range	Comment
  Glycine max	6 - 10	approx. 70% of maximal activity between pH 6 and pH 10
  Schizosaccharomyces pombe	7 - 9	stable enzyme, approx. 65% and unstable enzyme approx. 70% of maximal activity at pH 7, stable enzyme, approx. 75% and unstable enzyme approx. 65% of maximal activity at pH 9

Associated Proteins

Citations

• De novo purine nucleotide biosynthesis mediated by MoAde4 is required for conidiation, host colonization and pathogenicity in Magnaporthe oryzae.
• SHMT2 promotes the tumorigenesis of renal cell carcinoma by regulating the m6A modification of PPAT.
• Description of novel capsule biosynthesis loci of Campylobacter jejuni clinical isolates from South and South-East Asia.
• Multienzyme interactions of the de novo purine biosynthetic protein PAICS facilitate purinosome formation and metabolic channeling.
• Phosphoribosyltransferases and Their Roles in Plant Development and Abiotic Stress Response.
• Effects of Fructose and Palmitic Acid on Gene Expression in Drosophila melanogaster Larvae: Implications for Neurodegenerative Diseases.
• Erythritol alters gene transcriptome signatures, cell growth, and biofilm formation in Staphylococcus pseudintermedius.
• New In Vivo Approach to Broaden the Thioredoxin Family Interactome in Chloroplasts.
• Characterization of gut microbial and metabolite alterations in faeces of Goto Kakizaki rats using metagenomic and untargeted metabolomic approach.
• Porphyromonas gingivalis diffusible signaling molecules enhance Fusobacterium nucleatum biofilm formation via gene expression modulation.
• Comprehensive Bioinformatics Analysis of the Biodiversity of Lsm Proteins in the Archaea Domain.