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. It is also able to catalyze the dehydration of citrate and the hydration of cis-aconitate at a lower rate. Due to its broad substrate specificity, it seems to be responsible for the residual aconitase activity of the acnAB-null mutant. (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 2/2. Monomer. By propionate, but not acetate or glucose. Expression of prpBCDE operon is regulated by PrpR, CRP and a variety of sugars such as arabinose, galactose, glucose mannose and xylose. Cells lacking this gene abolished the residual aconitase activity of an AcnAB-null strain. PrpD catalyzes an unusual syn elimination, whereas the addition of water by AcnB to cis-2-methylaconitate occurs in the usual anti manner. Belongs to the PrpD family. There is uncertainty concerning the 2-methylcitrate stereochemistry. Brock et al. report a (2S,3S) stereochemistry, but Reddick et al. determined that the 2-methylcitrate has either (2S,3R) or (2R,3S) stereochemistry.