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. H2O + oxaloacetate + propanoyl-CoA = (2S,3S)-2-methylcitrate + CoA + H(+) acetyl-CoA + H2O + oxaloacetate = citrate + CoA + H(+) Organic acid metabolism; propanoate degradation. Carbohydrate metabolism; tricarboxylic acid cycle; isocitrate from oxaloacetate: step 1/2. Homodimer. Activated by PrpR. Cells lacking both prpC and prpD genes are unable to grow on propionate or cholesterol as the sole carbon source. The vitamin B12 restores growth of the prpDC mutant. It suggests the capacity of the MCM-dependent methylmalonyl pathway to support the metabolism of propionate independently of the methylcitrate cycle. Belongs to the citrate synthase family.