Involved in the methylaspartate cycle. Catalyzes the transfer of the CoA moiety from succinyl-CoA to mesaconate to generate mesaconyl-CoA (2-methylfumaryl-CoA) and succinate. mesaconate + succinyl-CoA = 2-methylfumaryl-CoA + succinate Belongs to the CoA-transferase III family. Extended N-terminus.