Involved in the assimilation of dimethylsulphoniopropionate (DMSP), an important compound in the fixation of carbon in marine phytoplankton. Catalyzes the ATP-dependent ligation of methylmercaptopropionate (MMPA) and CoA to yield methylmercaptopropionate-CoA (MMPA-CoA) (PubMed:21562561, PubMed:24443527). It is also active with short-chain-fatty-acid (carboxylic acids up to six carbons in length) (PubMed:21562561, PubMed:24443527). 3-(methylsulfanyl)propanoate + ATP + CoA = 3-(methylsulfanyl)propanoyl-CoA + AMP + diphosphate Activated by LiCl and NH(4)Cl. Inhibited by dimethylsulfoniopropionate (DMSP). MMPA concentrations above 2 mM relieve the DMSP inhibition and 80% of activity is regained at an MMPA concentration of 8 mM. kcat is 14.9 sec(-1) for ligase activity with MMPA as substrate. kcat is 7.2 sec(-1) for ligase activity with butyrate as substrate. kcat is 3.7 sec(-1) for ligase activity with propionate as substrate. kcat is 1 sec(-1) for ligase activity with acrylate as substrate. Optimum pH is between 7.5. Lipid metabolism; fatty acid metabolism. Homodimer. Cells lacking this gene show a delayed growth on methylmercaptopropionate (MMPA). Belongs to the ATP-dependent AMP-binding enzyme family.