Involved in the glyoxylate assimilation cycle used to regenerate acetyl-CoA and produce pyruvate as universal precursor for biosynthesis. Catalyzes the hydration of 3-methylfumaryl-CoA (mesaconyl-C4-CoA) to (3S)-citramalyl-CoA. (3S)-citramalyl-CoA = 3-methylfumaryl-CoA + H2O Inhibited by 3-methylfumaryl-CoA concentrations above 0.3 mM. kcat is 1045 sec(-1) for hydratase activity with 3-methylfumaryl-CoA (at 45 degrees Celsius). Homodimer. Belongs to the HTD2 family.