Catalyzes the decarboxylation of (R)-methylmalonyl-CoA to propionyl-CoA. Could be part of a pathway that converts succinate to propanoate. (R)-methylmalonyl-CoA + H(+) = CO2 + propanoyl-CoA Dimer of homotrimers. Belongs to the enoyl-CoA hydratase/isomerase family. Extended N-terminus.