A missense mutation (L166P) in DJ‐1, linked to familial Parkinson's disease, confers reduced protein stability and impairs homo‐oligomerization

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Abstract
The identification of genetic mutations responsible for rare familial forms of Parkinson's disease (PD) have provided tremendous insight into the molecular pathogenesis of this disorder. Mutations in the DJ‐1 gene cause autosomal recessive early onset PD in two European families. A Dutch kindred displays a large homozygous genomic deletion encompassing exons 1–5 of the DJ‐1 gene, whereas an Italian kindred harbors a single homozygous L166P missense mutation. A homozygous M26I missense mutation was also recently reported in an Ashkenazi Jewish patient with early onset PD. Mutations in DJ‐1 are predicted to be loss of function. The recent determination of the crystal structure of human DJ‐1 demonstrates that it exists in a homo‐dimeric form in vitro, whereas the L166P mutant exists only as a monomer. Here, we examine the in vivo effects of the pathogenic L166P and M26I mutations on the properties of DJ‐1 in cell culture. We report that the L166P mutation confers markedly reduced protein stability to DJ‐1, which results from enhanced degradation by the 20S/26S proteasome but not from a loss of mRNA expression. Furthermore, the L166P mutant protein exhibits an impaired ability to self‐interact to form homo‐oligomers. In contrast, the M26I mutation does not appear to adversely affect either protein stability, turnover by the proteasome, or the capacity of DJ‐1 to form homo‐oligomers. These properties of the L166P mutation may contribute to the loss of normal DJ‐1 function and are likely to be the underlying cause of early onset PD in affected members of the Italian kindred.