Cofactors

There are no Cofactors for this Enzyme

Reaction Mechanism

GMP synthase (glutamine-hydrolysing) By Reference

The Class I glutamine amidotransferase an example of a single enzymatic reaction being catalysed by two modules, each responsible for a distinct component of the reaction. It catalyses the amination of the nucleotide precursor xanthosine 5'-monophosphate to form GMP in the de novo purine biosynthesis pathway. The amidotransferase domain is found in related enzymes of the purine, pyrimidine, tryptophan, arginine, histidine and folic acid pathways. This domain includes a conserved Cys-His-Glu triad, responsible for the abstraction of the amide nitrogen from glutamine.

Despite the apparent catalytic readiness of the GMP synthetase active site, the Class I aminotransferase domain is actually a very poor glutaminase in the absence of the substrates XMP and ATP, which is consistent with the biological role of this enzyme, in which the hydrolysis of glutamine is tightly couple with the formation of GMP. The synthetase domain catalyses the addition of ammonia to an acceptor substrate. They are designed to work in concert to ensure efficient coupling of catalytic functions, it is suggested that a flexible hinge exists to bring the two sites together for concerted ammonia transfer.




• Summary
• Step 1
• Step 2
• Step 3
• Step 4
• Step 5
• Step 6
• Products

The beta-phosphate deprotonates the XMP substrate, which then initiates a nucleophilic attack on the alpha-phosphate of ATP, eliminating pyrophosphate aided by Asp239 and Lys381. His181 deprotonates Cys86, activating it for a nucleophilic attack upon L-glutamine, forming an enzyme-substrate covalent bond. The negative charge is stabilised, by an oxyanion hole involving Tyr87 and Gly59. The tetrahedral intermediate collapses, liberating ammonia, which deprotonates His181 and then passes to the other catalytic domain. Ammonia is deprotonated by the phosphate of the intermediate, activating it for a nucleophilic attack on the intermediate, which liberates AMP and the GMP product. In the glutamine site His181 deprotonates a water molecule, which initiates a nucleophilic attack on the Cys-bound intermediate. The tetrahedral intermediate collapses, liberating Cys86, which deprotonates His181, and the glutamate product.

Catalytic Residues

AA	Uniprot	Uniprot Resid	PDB	PDB Resid
His	P04079	181	1gpm	181
Lys	P04079	381	1gpm	381
Cys	P04079	86	1gpm	86
Tyr	P04079	87	1gpm	87
Glu	P04079	183	1gpm	183
Asp	P04079	239	1gpm	239
Gly	P04079	59	1gpm	59

Step Components

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



Step 1.

The beta-phosphate deprotonates the XMP substrate, which then initiates a nucleophilic attack on the alpha-phosphate of ATP, eliminating pyrophosphate.



Step 2.

His181 deprotonates Cys86, activating it for a nucleophilic attack upon L-glutamine, forming an enzyme-substrate covalent bond.



Step 3.

The tetrahedral intermediate collapses, liberating ammonia, which deprotonates His181 and then passes to the other catalytic domain. The ammonia produced is transferred from the glutaminase domain to the ATP pyrophosphatase domain. However, the glutaminase and ATP pyrophosphatase domain are approximately 30 Angstroms apart, and it is not yet entirely clear how the liberated ammonia is transported from the glutaminase to the ATP pyrophosphatase domain. It has been suggested that the most likely route is by channelling through the protein in a manner analogous to the classical channelling of common metabolites between sequential enzyme pairs [PMID:9575335]. However, a hinging movement between the two domains has also been suggested [PMID:8548458].



Step 4.

Ammonia is deprotonated by the phosphate of the intermediate, activating it for a nucleophilic attack on the intermediate, which liberates AMP and the GMP product.



Step 5.

His181 deprotonates a water molecule, which initiates a nucleophilic attack on the Cys-bound intermediate.



Step 6.

The tetrahedral intermediate collapses, liberating Cys86, which deprotonates His181, and the glutamate product.



Products.

The products of the reaction.

View Reaction Mechanisms in M-CSA

Reaction Parameters

There are no kinetic parameters information for this Enzyme

Associated Proteins

Citations

• Micromonospora profundi TRM 95458 converts glycerol to a new osmotic compound.
• Organ agar serves as physiologically relevant alternative for in vivo bacterial colonization.
• Mechanistic Insights into the Functioning of a Two-Subunit GMP Synthetase, an Allosterically Regulated, Ammonia Channeling Enzyme.
• Structural insights into the antifungal drug target guanosine monophosphate synthase from Aspergillus fumigatus.
• Metabolomic Analysis of Key Metabolites and Their Pathways Revealed the Response of Alfalfa (Medicago sativa L.) Root Exudates to rac-GR24 under Drought Stress.
• Protective Effect of Glycomacropeptide on the Inflammatory Response of U937 Macrophages.
• Tertiary and Quaternary Structure Organization in GMP Synthetases: Implications for Catalysis.
• Porphyromonas gingivalis diffusible signaling molecules enhance Fusobacterium nucleatum biofilm formation via gene expression modulation.
• Comparative transcriptome analysis reveals molecular regulation of salt tolerance in two contrasting chickpea genotypes.
• E. coli "Stablelabel" S30 lysate for optimized cell-free NMR sample preparation.
• Global Analysis of Post-Translational Side-Chain Arginylation Using Pan-Arginylation Antibodies.