Involved in the methylaspartate cycle. Catalyzes the reversible hydration of mesaconyl-CoA (2-methylfumaryl-CoA) to yield beta-methylmalyl-CoA ((2R,3S)-beta-methylmalyl-CoA) (PubMed:28932214). Shows also activity with mesaconyl-C4-CoA (3-methylfumaryl-CoA), (S)-citramalyl-CoA and (S)-malyl-CoA (PubMed:28932214). (2R,3S)-beta-methylmalyl-CoA = 2-methylfumaryl-CoA + H2O Shows highest activity at 0.5 M KCl. Does not require divalent ions for activity. Homodimer. Belongs to the enoyl-CoA hydratase/isomerase family.