The identification of monogenic variants of Parkinson’s disease (PD) has provided novel insights into its unknown pathogenesis. As the first protein linked to autosomal-recessive forms of PD, Parkin became a welcome tool to explain biochemical and neuropathological observations that had suggested involvement of the ubiquitin-proteasome system (UPS) in PD. Based on cellular expression studies and biochemical in vitro experiments, several researchers ascribed an E3-type, E2-dependent ubiquitin protein ligase activity to wild-type (but not mutant) Parkin proteins. Although the individual components of the proposed Parkin ubiquitin ligase complex in the normal human brain remain to be identified and the E3 ligase effect of Parkin function has not yet been confirmed in an animal model, the scientific exploration of a protein with several links to the UPS has provided many leads in PD research. This chapter describes assays that the authors have used to examine the cellular and in vitro effects of neural Parkin.
