Alpha-oxoaldehydes such as methylglyoxal (MGO) and glyoxal (GO) are highly reactive as to modify cellular macromolecules, causing cell death. The major system known to detoxify such compounds includes glyoxalase I and II that requires glutathione (GSH) as a co-factor. Here we characterized two homologs of human DJ-1, a protein associated with Parkinson’s disease, in C.elegans as novel glyoxalases. The two homologs, each named DJR-1.1 and DJR-1.2, share high structural similarity with human DJ-1 and have superimposable catalytic residues for its enzymatic activity. Purified DJR-1.1 and DJR-1.2 proteins showed activities against both methylglyoxal and glyoxal, yielding lactic acid and glycolic acid as products, respectively. Activities of worm extracts from wild type and knockout DJR mutant C. elegans also showed that both DJR-1.1 and DJR-1.2 exert glyoxalase activities in tissue extracts. Endogenous glyoxal levels of DJR mutants were significantly higher than that of wild type worms under normal conditions, and aging of these mutants lead to higher levels of glyoxal-induced Nε-carboxymethyl lysine (CML), one of the deleterious advanced glycation end products (AGEs) caused by glyoxal. DJR-1.1 was expressed throughout the intestine of worms, locating in both nucleus and cytoplasm, while DJR-1.2 was expressed in the cytoplasm of various chemosensory neurons and glial cells. The expression of DJR-1.2 was dramatically increased when worms were starved and entered the dauer stage, which was correlated with an increase in its enzymatic activity. The dauer-specific expression of DJR-1.2 depends on DAF-16 transcription regulator, a homologue of mammalian FOXO. The C.elegans mutants of DJR-1.1 and DJR-1.2 exhibited varying degrees of sensitivities to glyoxal and methylglyoxal, which were rescued by corresponding transgenics, although normal life spans of these mutants were essentially unchanged. Mutants of DJR-1.2 also lead to a significant loss of dopaminergic neurons caused by methylglyoxal or glyoxal, which were rescued by corresponding transgenics. We concluded that the C.elegans DJRs plays a critical role in the removal of α-oxoaldehydes, protecting worms from neurodegeneration and death caused by carbonyl stress.
DJ-1은 파킨슨병(Parkinson`s disease)의 초기 발병 원인 유전자로 알려져 있다. 이 유전자는 최초에 종양유전자로서 발견되었고, 이 단백질은 산화적 스트레스로부터 세포를 보호하는 작용과, MPP+, 6-OHDA 및 로테논 (rotenone)과 같은 PD-유발자에 대한 신경보호작용을 포함한 다양한 작용을 한다는 것이 보고되었다. 본 연구에서는 인간 DJ-1 단백질의 유사체를 녹아웃 시킨 선충에서 반응성 전자 친화물질인 글리옥살과 메틸글리옥살을 처리한 경우 선충 (Caenorhabditis elegans)의 죽음과 도파민성 신경 손실을 확인하였다. 선충은 2개의 DJ-1 유사체를 가지고 있는데 DJR-1.1은 주로 장에서 발현되며, DJR-1.2는 뉴런을 포함하는 머리 부위에서 발현된다. DJR-1.1/1.2를 녹아웃시킨 경우 수명에는 영향이 없었다. 그러나 글리옥살 혹은 메틸글리옥살 처리 후에는 녹아웃 균주가 생존률이 낮아지는 것을 보이며, DJR-1.2의 녹아웃 균주는 도파민 신경세포 손실이 더 크게 나타나는 것을 확인하였다. 이 DJR-1.2는 선충이 휴면기에 들어갈 경우 발현이 증가되며 이 발현증가는 DAF-16이라는 유전자 발현조절 인자에 의한 것으로 드러났다. DJR-1.2의 발현이 증가할 경우 글리옥살라제로서의 효소의 활성도 함께 증가하는 것으로 나타났다. 이러한 발견들은 DJ-1 단백질이 반응성 카르보닐 종의 소거자로 작용한다는 것을 증명한 것이며, 파킨슨병 발병 원인에 새로운 관점을 제시할 것으로 기대하고 있다.
