The DJ-1L166P mutant protein associated with early onset Parkinson's disease is unstable and forms higher-order protein complexes

Parkinson's disease (PD) is a common neurodegenerative disorder that involves the selective degeneration of midbrain dopaminergic neurons. Recently DJ-1 mutations have been linked to autosomal-recessive early-onset Parkinsonism in two European families. By using gel filtration assays under physiological conditions we demonstrate that DJ-1 protein forms a dimeric structure. Conversely, the DJ-1(L166P) mutant protein shows a different elution profile as compared with DJ-1(WT) both in overexpression cellular systems or in lymphoblasts cells, suggesting that it might form higher order protein structures. Furthermore we observed that the level of DJ-1(L166P) mutant protein in the patient's lymphoblasts was very low as compared with the wild-type protein. We excluded a potential transcriptional impairment by performing quantitative RT-PCR on the patient's material. Pulse-chase experiments in transfected COS-1 cells and cycloheximide treatment in control and patient lymphoblasts indicated that the mutant protein was rapidly degraded. This rapid turnover and the structural changes of DJ-1(L166P) mutant protein might be crucial in the disease pathogenesis.