Cellular parkin mutants are soluble under non-stress conditions.

The parkin gene encodes an E3 ubiquitin ligase and loss of function mutations herein are the most frequent cause of early-onset Parkinson's disease. Reports have suggested that aggregation of mutant protein is the cause of the loss of function. We established stably transfected SH-SY5Y dopaminergic cell lines expressing wild-type and mutant parkin proteins. All the mutant proteins were soluble but could be rendered insoluble by subjecting the cellsto stress by proteasomal inhibition, treatment with oxidants and upon transient expression of the mutant proteins. A functional assay demonstrated that the R42P mutant retained functional activity in contrast to the W453stop mutant. Accordingly, the functional impairment by the mutations is not simply caused by turning the proteins insoluble.