Human DJ-1 is a genetic cause of early-onset Parkinson's disease (PD), although its biochemical function is unknown. We report here that human DJ-1 and its homologs of the mouse and Caenorhabditis elegans are novel types of glyoxalase, converting glyoxal or methylglyoxal to glycolic or lactic acid, respectively, in the absence of glutathione. Purified DJ-1 proteins exhibit typical Michaelis–Menten kinetics, which were abolished completely in the mutants of essential catalytic residues, consisting of cysteine and glutamic acid. The presence of DJ-1 protected mouse embryonic fibroblast and dopaminergically derived SH-SY5Y cells from treatments of glyoxals. Likewise, C. elegans lacking cDJR-1.1, a DJ-1 homolog expressed primarily in the intestine, protected worms from glyoxal-induced death. Sub-lethal doses of glyoxals caused significant degeneration of the dopaminergic neurons in C. elegans lacking cDJR-1.2, another DJ-1 homolog expressed primarily in the head region, including neurons. Our findings that DJ-1 serves as scavengers for reactive carbonyl species may provide a new insight into the causation of PD.

Summary: Hsp31 encoded by hchA is known as a heat‐inducible molecular chaperone. Although structure studies revealed that Hsp31 has a putative catalytic triad consisting of Asp‐214, His‐186 and Cys‐185, its enzymatic function, besides weak amino‐peptidase activity, is still unknown. We found that Hsp31 displays glyoxalase activity that catalyses the conversion of methylglyoxal (MG) to d‐lactate without an additional cofactor. The glyoxalase activity was completely abolished in the hchA‐deficient strain, confirming the relationship between the hchA gene and its enzymatic activity in vivo. Hsp31 exhibits Michaelis–Menten kinetics for substrates MG with K_m and k_cat of 1.43 ± 0.12 mM and 156.9 ± 5.5 min⁻¹ respectively. The highest glyoxalase activity was found at 35–40°C and pH of 6.0–8.0, and the activity was significantly inhibited by Cu²⁺, Fe³⁺ and Zn²⁺. Mutagenesis studies based on our evaluation of conserved catalytic residues revealed that the Cys‐185 and Glu‐77 were essential for catalysis, whereas His‐186 was less crucial for enzymatic function, although it participates in the catalytic process. The stationary‐phase Escherichia coli cells became more susceptible to MG when hchA was deleted, which was complemented by an expression of plasmid‐encoded hchA. Furthermore, an accumulation of intracellular MG was observed in hchA‐deficient strains.

Glyoxal (GO) and methylglyoxal (MG), belonging to α-oxoaldehydes, are produced by organisms from bacteria to humans by glucose oxidation, lipid peroxidation, and DNA oxidation. Since glyoxals contain two adjacent reactive carbonyl groups, they are referred to as reactive electrophilic species (RES), and are damaging to proteins and nucleotides. Therefore, glyoxals cause various diseases in humans, such as diabetes and neurodegenerative diseases, from which all living organisms need to be protected. Although the glyoxalase system has been known for some time, details on how glyoxals are sensed and detoxified in the cell have not been fully elucidated, and are only beginning to be uncovered. In this review, we will summarize the current knowledge on bacterial responses to glyoxal, and specifically focus on the glyoxal-associated regulators YqhC and NemR, as well as their detoxification mediated by glutathione (GSH)-dependent/independent glyoxalases and NAD(P)H-dependent reductases. Furthermore, we will address questions and future directions.

Methylglyoxal (MG) is a toxic metabolite known to accumulate in various cell types. We detected in vivo conversion of MG to acetol in MG-accumulating Escherichia coli cells by use of ¹ H nuclear magnetic resonance ( ¹ H-NMR) spectroscopy. A search for homologs of the mammalian aldo-keto reductases (AKRs), which are known to exhibit activity to MG, revealed nine open reading frames from the E. coli genome. Based on both sequence similarities and preliminary characterization with ¹ H-NMR for crude extracts of the corresponding mutant strains, we chose five genes, yafB , yqhE , yeaE , yghZ , and yajO , for further study. Quantitative assessment of the metabolites produced in vitro from the crude extracts of these mutants and biochemical study with purified AKRs indicated that the yafB , yqhE , yeaE , and yghZ genes are involved in the conversion of MG to acetol in the presence of NADPH. When we assessed their in vivo catalytic activities by creating double mutants, all of these genes except for yqhE exhibited further sensitivities to MG in a glyoxalase-deficient strain. The results imply that the glutathione-independent detoxification of MG can occur through multiple pathways, consisting of yafB , yqhE , yeaE , and yghZ genes, leading to the generation of acetol.

The reactive α-oxoaldehydes such as glyoxal (GO) and methylglyoxal (MG) are generated in vivo from sugars through oxidative stress. GO and MG are believed to be removed from cells by glutathione-dependent glyoxalases and other aldehyde reductases. We isolated a number of GO-resistant (GO ^r ) mutants from Escherichia coli strain MG1655 on LB plates containing 10 mM GO. By tagging the mutations with the transposon Tn phoA -132 and determining their cotransductional linkages, we were able to identify a locus to which most of the GO ^r mutations were mapped. DNA sequencing of the locus revealed that it contains the yqhC gene, which is predicted to encode an AraC-type transcriptional regulator of unknown function. The GO ^r mutations we identified result in missense changes in yqhC and were concentrated in the predicted regulatory domain of the protein, thereby constitutively activating the product of the adjacent gene yqhD . The transcriptional activation of yqhD by wild-type YqhC and its mutant forms was established by an assay with a β-galactosidase reporter fusion, as well as with real-time quantitative reverse transcription-PCR. We demonstrated that YqhC binds to the promoter region of yqhD and that this binding is abolished by a mutation in the potential target site, which is similar to the consensus sequence of its homolog SoxS. YqhD facilitates the removal of GO through its NADPH-dependent enzymatic reduction activity by converting it to ethadiol via glycolaldehyde, as detected by nuclear magnetic resonance, as well as by spectroscopic measurements. Therefore, we propose that YqhC is a transcriptional activator of YqhD, which acts as an aldehyde reductase with specificity for certain aldehydes, including GO.

Canine preaxial polydactyly (PPD) in the hind limb is a developmental trait that restores the first digit lost during canine evolution. Using a linkage analysis, we previously demonstrated that the affected gene in a Korean breed is located on canine chromosome 16. The candidate locus was further limited to a linkage disequilibrium (LD) block of <213 kb composing the single gene, LMBR1, by LD mapping with single nucleotide polymorphisms (SNPs) for affected individuals from both Korean and Western breeds. The ZPA regulatory sequence (ZRS) in intron 5 of LMBR1 was implicated in mammalian polydactyly. An analysis of the LD haplotypes around the ZRS for various dog breeds revealed that only a subset is assigned to Western breeds. Furthermore, two distinct affected haplotypes for Asian and Western breeds were found, each containing different single-base changes in the upstream sequence (pZRS) of the ZRS. Unlike the previously characterized cases of PPD identified in the mouse and human ZRS regions, the canine mutations in pZRS lacked the ectopic expression of sonic hedgehog in the anterior limb bud, distinguishing its role in limb development from that of the ZRS.