Catalyzes the conversion of methylglyoxal (MG) to D-lactate in a single glutathione (GSH)-independent step. Selective for MG, does not use glyoxal as substrate. Plays a role in detoxifying endogenously produced MG, particularly when glycerol is the principal carbon source (PubMed:24302734). Important for viability in stationary phase (By similarity). H2O + methylglyoxal = (R)-lactate + H(+) kcat is 7.8 sec(-1) with methylglyoxal as substrate. Monomer. Has a 3- to 5-fold increase in levels of intracellular methylglyoxal compared with wild-type cells grown in the same media. Belongs to the peptidase C56 family. HSP31-like subfamily.