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 dehydration of 2-methylcitrate (2-MC) to yield the cis isomer of 2-methyl-aconitate (PubMed:18375549, PubMed:22365605). Could also catalyze the dehydration of citrate and the hydration of cis-aconitate (By similarity). (2S,3S)-2-methylcitrate = 2-methyl-cis-aconitate + H2O citrate = D-threo-isocitrate Organic acid metabolism; propanoate degradation. Carbohydrate metabolism; tricarboxylic acid cycle; isocitrate from oxaloacetate: step 1/2. Monomer. 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 on propionate as the sole carbon source. It suggests the capacity of the MCM-dependent methylmalonyl pathway to support the metabolism of propionate independently of the methylcitrate cycle. Belongs to the PrpD family.