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Oxalyl-CoA decarboxylase
In enzymology, an oxalyl-CoA decarboxylase (OXC) () is an enzyme primarily produced by the gastrointestinal bacterium Oxalobacter formigenes that catalyzes the chemical reaction
:oxalyl-CoA formyl-CoA + CO2
OXC belongs to the family of lyases, specifically the carboxy-lyases, which cleave carbon-carbon bonds. The systematic name of this enzyme class is oxalyl-CoA carboxy-lyase (formyl-CoA-forming). Other names in common use include oxalyl coenzyme A decarboxylase, and oxalyl-CoA carboxy-lyase. This enzyme participates in glyoxylate and dicarboxylate metabolism. It employs one cofactor, thiamin diphosphate (TPP), and plays a key role in catabolism of oxalate, a highly toxic compound that is a product of the oxidation of carbohydrates in many bacteria and plants.〔Baetz, A.L. and Allison, M.J. “Purification and characterization of formyl-coenzyme A transferase from Oxalobacter formigenes.” J. Bacteriol 172, 7 (1990).〕 Oxalyl-CoA decarboxylase is extremely important for the elimination of ingested oxalates found in human foodstuffs like coffee, tea, and chocolate,〔Gasinka, A. and Gajewska, D. “Tea and Coffee as the Main Source of Oxalate in Diets of Patients with Kidney Oxalate Stones.” Roczn. Pzh 58, 1 (2007).〕 and the ingestion of such foods in the absence of Oxalobacter formigenes in the gut can result in kidney disease or even death as a result of oxalate poisoning.〔Turoni, S. ''et al''. “Oxalate-degrading activity in Bifidobacterium animalis subsp. lactis: impact of acidic conditions on the transcriptional levels of the oxalyl coenzyme A (CoA) decarboxylase and formyl-CoA transferase genes.” Appl. Environ. Microbiol. 76, 10 (2010).〕
==Evolution==
Oxalyl-CoA decarboxylase is hypothesized to be evolutionarily related to acetolactate synthase, a TPP-dependent enzyme responsible for the biosynthesis of branched chain amino acids in certain organisms.〔Dailey, F.E and Cronan, J.E. “Acetohydroxy acid synthase I, a required enzyme for isoleucine and valine biosynthesis in Escherichia coli K-12 during growth on acetate as the sole carbon source." J. Bacteriol 165, 2 (1986).〕 Sequence alignments between the two enzymes support this claim, as do the presence of vestigial FAD-binding pockets that play no role in either enzyme’s catalytic activity.〔Chipman, D. ''et al''. “Biosynthesis of 2-aceto-2-hydroxy acids: acetolactate synthases and acetohydroxyacid synthases.” Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology 1385, 2 (1998).〕 The binding of FAD at this site in acetolactate synthase and the binding of ADP at a cognate site in OXC are thought to play roles in the stabilization of the tertiary structures of the proteins.〔Signh, B.K. and Schmitt, G.K. “Flavin adenine dinucleotide causes oligomerization of acetohydroxyacid synthase from black Mexican sweet corn cells.” FEBS Letters 258, 1 (1989).”〕 No FAD binding is observed in oxalyl-CoA decarboxylase,〔Svedruzic, D. ''et al''. “The enzymes of oxalate metabolism: unexpected structures and mechanisms.” Archives of Biochemistry and Biophysics 433, 1 (2005).〕 but an excess of coenzyme A in the crystal structure has led to the hypothesis that the binding site was co-opted during OXC evolution to bind the CoA moiety of its substrate.〔Berthold, C.L. ''et al''. “Crystallographic Snapshots of Oxalyl-CoA Decarboxylase Give Insights into Catalysis by Nonoxidative ThDP-Dependent Decarboxylases.” Structure 15, 7 (2007).〕 Despite their similarities, only oxalyl-CoA decarboxylase is necessary for the formation of ATP in Oxalobacter formigenes, and exogenous ADP has been demonstrated to increase the decarboxylase activity of OXC, but not acetolactate synthase.〔Maestri, O. and Joset, F. “Regulation by external pH and stationary growth phase of the acetolactate synthase from Synechocystis PCC6803.” Mol.Microbiol. 37, 4 (2000).〕〔Whitlow, K.J. and Polgase, W.J. “Regulation of acetohydroxy acid synthase in streptomycin-dependent Escherichia coli.” J. Bacteriol 121, 1 (1970).〕
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