Involved in the catabolism of short chain fatty acids (SCFA) via the tricarboxylic acid (TCA)(acetyl degradation route) and via the 2-methylcitrate cycle I (propionate degradation route). Catalyzes the Claisen condensation of propionyl-CoA and oxaloacetate (OAA) to yield 2-methylcitrate (2-MC) and CoA. Also catalyzes the condensation of oxaloacetate with acetyl-CoA but with a lower specificity. H2O + oxaloacetate + propanoyl-CoA = (2S,3S)-2-methylcitrate + CoA + H(+) acetyl-CoA + H2O + oxaloacetate = citrate + CoA + H(+) kcat is 8 sec(-1) for 2-methylcitrate synthase activity with propionyl-CoA as substrate (at pH 8 and 23 degrees Celsius). kcat is 21 sec(-1) for citrate synthase activity with acetyl-CoA as substrate (at pH 8 and 23 degrees Celsius). Optimum temperature is 31 degrees Celsius. Cold-active. Is rapidly inactivated at 45 degrees Celsius, and shows significant activity at 10 degrees Celsius and below. Organic acid metabolism; propanoate degradation. Carbohydrate metabolism; tricarboxylic acid cycle; isocitrate from oxaloacetate: step 1/2. Homodimer. By growth on propionate, but not acetate or glucose. Belongs to the citrate synthase family.