Involved in the 3-hydroxypropionate cycle used for autotrophic carbon dioxide fixation. Catalyzes the transfer of CoA moiety from succinyl-CoA to L-malate to yield L-malyl-CoA. It is highly specific for succinyl-CoA as the CoA donor, however it can accept L-citramalate instead of L-malate as the CoA acceptor. (S)-malate + succinyl-CoA = (S)-malyl-CoA + succinate (3S)-citramalate + succinyl-CoA = (3S)-citramalyl-CoA + succinate Optimum pH is 6.5. Optimum temperature is 55 degrees Celsius. Forms a large complex composed of six heterodimers (alpha, beta). Under autotrophic growth conditions. Belongs to the CoA-transferase III family.