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Structural Basis for Activation of the Thiamin Diphosphate-dependent Enzyme Oxalyl-CoA Decarboxylase by Adenosine Diphosphate * S Received for publication, September 8, 2005, and in revised form, October 7, 2005 Published, JBC Papers in Press, October 10, 2005, DOI 10.1074/jbc.M509921200 Catrine L. Berthold , Patricia Moussatche § , Nigel G. J. Richards § , and Ylva Lindqvist ‡1 From the Molecular Structural Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, S-17177 Stockholm, Sweden and the § Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200 Oxalyl-coenzyme A decarboxylase is a thiamin diphosphate-de- pendent enzyme that plays an important role in the catabolism of the highly toxic compound oxalate. We have determined the crystal structure of the enzyme from Oxalobacter formigenes from a hemi- hedrally twinned crystal to 1.73 A ˚ resolution and characterized the steady-state kinetic behavior of the decarboxylase. The monomer of the tetrameric enzyme consists of three ± / ² -type domains, com- monly seen in this class of enzymes, and the thiamin diphosphate- binding site is located at the expected subunit-subunit interface between two of the domains with the cofactor bound in the con- served V-conformation. Although oxalyl-CoA decarboxylase is structurally homologous to acetohydroxyacid synthase, a molecule of ADP is bound in a region that is cognate to the FAD-binding site observed in acetohydroxyacid synthase and presumably fulfils a similar role in stabilizing the protein structure. This difference between the two enzymes may have physiological importance since oxalyl-CoA decarboxylation is an essential step in ATP generation in O. formigenes , and the decarboxylase activity is stimulated by exogenous ADP. Despite the significant degree of structural conser- vation between the two homologous enzymes and the similarity in catalytic mechanism to other thiamin diphosphate-dependent enzymes, the active site residues of oxalyl-CoA decarboxylase are unique. A suggestion for the reaction mechanism of the enzyme is presented. Oxalic acid is one of nature’s most highly oxidized organic com- pounds, and its dianion is a strong chelator of metal cations, especially Ca 2 ± , causing oxalate to be highly toxic to many organisms (1). In humans, elevated levels of oxalate are associated with several diseases, including the formation of calcium oxalate stones in the kidney (uroli- thiasis), renal failure, cardiomyopathy, and cardiac conductance disor- ders (1–3). Relatively large amounts of oxalate are introduced into the body through the diet, although this diacid may also arise as a byproduct of normal cellular metabolism (4). Because humans, in common with other mammals, are not able to degrade oxalate, this compound must be eliminated by excretion in the urine or via the intestine (5). The recent observation that a symbiotic, gut-dwelling bacterium, Oxalobacter for- migenes
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