Cofactors

Thiamine diphosphate.

Reaction Mechanism

tartronate-semialdehyde synthase By Reference

Glyoxylate carboligase, also called tartronate-semialdehyde synthase, releases carbon dioxide while synthesising a single molecule of tartronate semialdehyde from two molecules of glyoxylate. It is a thiamine pyrophosphate-dependent enzyme, closely related in sequence to the large subunit of acetolactate synthase. In the D-glycerate pathway, part of allantoin degradation in the Enterobacteriaceae, tartronate semialdehyde is converted to D-glycerate and then 3-phosphoglycerate, a product of glycolysis and entry point in the general metabolism.




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

This enzyme utilises a thiamine diphosphate cofactor to catalyse the condensation reaction between two molecules of glyoxylate. The mechanism, however, does not begin with a proton transfer to a conserved gluatmate, as is the case for every other enzyme that uses this cofactor. Instead, the aliphatic residues surrounding the cofactor act to lower the dielectric constant of the active site, leading to activation of the cofactor by intramolecular proton rearrangement.

Catalytic Residues

AA	Uniprot	Uniprot Resid	PDB	PDB Resid
Leu	P0AEP7	421	2pan	444
Ile	P0AEP7	479	2pan	502
Leu	P0AEP7	476	2pan	499
Val	P0AEP7	25	2pan	48
Val	P0AEP7	51	2pan	74

Step Components

overall reactant used, proton transfer, overall product formed, intramolecular elimination, bimolecular nucleophilic addition, native state of cofactor regenerated, intermediate formation, native state of enzyme regenerated, inferred reaction step, cofactor used



Step 1.

The cofactor undergoes an intramolecular proton transfer between the pyrimidine and thiazole ring, forming a carbon-nitrogen ylid.



Step 2.

The carbanion of thiamine diphosphate initiates a nucleophilic attack on the carbonyl carbon of glyoxylate in an addition reaction. The conjugated double bond system of the cofactor undergoes rearrangement.



Step 3.

The glyoxylate-TDP adduct undergoes decarboxylation with concomitant bond rearrangement on the thiazole ring. The aliphatic region around the cofactor encourages decarboxylation through polar, non-polar interactions, which act to increase the ground state energy of the intermediate towards that of the transition state [PMID:18176558, PMID:15501823, PMID:15709735]



Step 4.

The nitrogen of the thiazole ring initiates conjugate nucleophilic attack at the carbonyl of the second glyoxylate molecule, with inferred, concomitant, intramolecular proton rearrangement.



Step 5.

The oxyanion initiates elimination, forming the single S enantiomer of 2-Hydroxy-3-oxopropanoate and regenerating the activated form of the thiamine diphosphate cofactor.



Step 6.

Protonation at the C2 position regenerates the thiamine diphosphate cofactor, and the enzyme active site.



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

• A systematic overexpression approach reveals native targets to increase squalene production in Synechocystis sp. PCC 6803.
• Anaerobic Microbial Metabolism of Dichloroacetate.
• Adaption and Degradation Strategies of Methylotrophic 1,4-Dioxane Degrading Strain Xanthobacter sp. YN2 Revealed by Transcriptome-Scale Analysis.
• TCA Cycle Replenishing Pathways in Photosynthetic Purple Non-Sulfur Bacteria Growing with Acetate.
• E. coli allantoinase is activated by the downstream metabolic enzyme, glycerate kinase, and stabilizes the putative allantoin transporter by direct binding.
• In-Depth Computational Analysis of Natural and Artificial Carbon Fixation Pathways.
• Phosphoglycolate salvage in a chemolithoautotroph using the Calvin cycle.
• Engineering Escherichia coli for the utilization of ethylene glycol.
• Production of 3-Hydroxypropionic Acid from Renewable Substrates by Metabolically Engineered Microorganisms: A Review.
• Biotechnological Plastic Degradation and Valorization Using Systems Metabolic Engineering.
• Integrated Metabolome and Transcriptome Analysis of Fruit Flavor and Carotenoids Biosynthesis Differences Between Mature-Green and Tree-Ripe of cv. "Golden Phoenix" Mangoes (Mangifera indica L.).