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.
Methylglyoxal (MG) is a highly reactive metabolic intermediate, presumably accumulated during uncontrolled carbohydrate metabolism. The major source of MG is dihydroxyacetone phosphate, which is catalyzed by MG synthase (the mgs product) in bacteria. We observed Escherichia coli cell death when the ribose transport system, consisting of the RbsDACBK proteins, was overproduced on multicopy plasmids. Almost 100% of cell death occurs a few hours after ribose addition (>10 mM), due to an accumulation of extracellular MG as detected by 1 H-nuclear magnetic resonance ( 1 H-NMR). Under lethal conditions, the concentration of MG produced in the medium reached approximately 1 mM after 4 h of ribose addition as measured by high-performance liquid chromatography. An excess of the protein RbsD, recently characterized as a mutarotase that catalyzes the conversion between the -pyran and -furan forms of ribose, was critical in accumulating the lethal level of MG, which was also shown to require ribokinase (RbsK). The intracellular level of ribose 5-phosphate increased with the presence of the protein RbsD, as determined by 31 P-NMR. As expected, a mutation in the methylglyoxal synthase gene (mgs) abolished the production of MG. These results indicate that the enhanced ribose uptake and incorporation lead to an accumulation of MG, perhaps occurring via the pentose-phosphate pathway and via glycolysis with the intermediates fructose 6-phosphate and glyceraldehyde 3-phosphate. It was also demonstrated that a small amount of MG is synthesized by monoamine oxidase.
In this study, we simulated space flight of the nematode, Caenorhabditis elegans, on the ground and examined how it is affected by space radiation and G-forces. We simulated G-forces during launch in a gravity acceleration laboratory device in order to identify and isolate the effects of the G-forces. Following this, we irradiated C. elegans with accelerated protons (MC-50 Cyclotron) and gamma rays (iR 222 machine) at the same physical dose. We calculated the expected radiation dose according to Reitz [1] and simulation programs (NASA AP8MIN [2], NASA AE8MAX [2], and CREAM86 [3]) for 1 month (dose rate: 6 × 10 −3 Gy; 2.8 × 10 −2 Gy), 6 months (dose rate: 36 × 10 −3 Gy; 16.8 × 10 −2 Gy), and 2 years (dose rate: 144 × 10 −3 Gy; 67.2 × 10 −2 Gy) of space flight. There have been several trials that aimed to take C. elegans into orbit on US space shuttle missions including a mission on the shuttle Columbia. In this study, we simulated longer duration space flights and performed a whole-genome microarray analysis to observe phenotype variations whereas most such experiments were carried out during short duration space flights and focused on mutations and genotypic variations. We expect that the results of this study will be useful to predict the effects of long-term exposure of space radiation on living organisms.
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