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2JI8: X-Ray Structure Of Oxalyl-Coa Decarboxylase In Complex With Formyl-Coa
Crystallographic snapshots of oxalyl-CoA decarboxylase give insights into catalysis by nonoxidative ThDP-dependent decarboxylases
Structure (2007) 15 p.853-861
Despite more than five decades of extensive studies of thiamin diphosphate (ThDP) enzymes, there remain many uncertainties as to how these enzymes achieve their rate enhancements. Here, we present a clear picture of catalysis for the simple nonoxidative decarboxylase, oxalyl-coenzyme A (CoA) decarboxylase, based on crystallographic snapshots along the catalytic cycle and kinetic data on active site mutants. First, we provide crystallographic evidence that, upon binding of oxalyl-CoA, the C-terminal 13 residues fold over the substrate, aligning the substrate alpha-carbon for attack by the ThDP-C2 atom. The second structure presented shows a covalent reaction intermediate after decarboxylation, interpreted as being nonplanar. Finally, the structure of a product complex is presented. In accordance with mutagenesis data, no side chains of the enzyme are implied to directly participate in proton transfer except the glutamic acid (Glu-56), which promotes formation of the 1',4'-iminopyrimidine tautomer of ThDP needed for activation.
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