Involved in the catabolism of oxalate and in the adapatation to low pH via the induction of the oxalate-dependent acid tolerance response (ATR). Catalyzes the decarboxylation of oxalyl-CoA to yield carbon dioxide and formyl-CoA. H(+) + oxalyl-CoA = CO2 + formyl-CoA Binds 1 Mg(2+) ion per subunit. Binds 1 thiamine pyrophosphate per subunit. Activated by ADP. kcat is 69.7 sec(-1) for decarboxylase activity with oxalyl-CoA as substrate (with 300 uM ADP at pH 6.5 and 30 degrees Celsius). kcat is 60.7 sec(-1) for decarboxylase activity with oxalyl-CoA as substrate (at pH 6.5 and 30 degrees Celsius). Optimum pH is between 5.5 and 7. Metabolic intermediate degradation; oxalate degradation; CO(2) and formate from oxalate: step 2/2. Homotetramer; dimer of dimers. By the acid response regulator EvgA. Belongs to the TPP enzyme family.