Aberrant folding of pathogenic Parkin mutants: aggregation versus degradation

Loss-of-function mutations in the Parkin gene (PARK2) are responsible for the majority of autosomal recessive Parkinson disease. A growing body of evidence indicates that misfolding and aggregation of Parkin is a major mechanism of Parkin inactivation, accounting for the loss-of-function phenotype of various pathogenic Parkin mutants. Remarkably, wild-type Parkin is also prone to misfolding under certain cellular conditions, suggesting a more general role of Parkin in the pathogenesis of Parkinson disease. We now show that misfolding of Parkin can lead to two phenotypes: the formation of detergent-insoluble, aggregated Parkin, or destabilization of Parkin resulting in an accelerated proteasomal degradation. By combining two pathogenic Parkin mutations, we could demonstrate that destabilization of Parkin is dominant over the formation of detergent-insoluble Parkin aggregates. Furthermore, a comparative analysis with HHARI, an E3 ubiquitin ligase with an RBR domain highly homologous to that of Parkin, revealed that folding of Parkin is specifically dependent on the integrity of the C-terminal domain, but not on the presence of a putative PDZ-binding motif at the extreme C terminus.