Kinetic evidence in favor of glyoxalase III and against deglycase activity of DJ-1

DJ-1, a protein encoded by PARK7 plays a protective role against neurodegeneration. Since its glyoxalase III activity catalyzing methylglyoxal (MG) to lactate was discovered, DJ-1 has been re-established as a deglycase decomposing the MG-intermediates with amino acids and nucleotides (hemithioacetal and hemiaminal) rather than MG itself, but it is still debatable. Here, we have clarified that human DJ-1 directly recognizes MG, and not MG-intermediates, by monitoring the detailed catalytic processes and enantiomeric lactate products. The hemithioacetal intermediate between C106 of ¹⁵ N-labeled DJ-1 (^15N DJ-1) and MG was also monitored by NMR. TRIS molecule formed stable diastereotopic complexes with MG (K_d , 1.57 ± 0.27 mM) by utilizing its three OH groups, which likely disturbed the assay of deglycase activity. The low k_cat of DJ-1 for MG and its MG-induced structural perturbation may suggest that DJ-1 has a regulatory function as an in vivo sensor of reactive carbonyl stress.