A mechanistic review of Parkin activation.

Parkin and phosphatase and tensin homolog (PTEN)-induced kinase 1 (PINK1) constitute a feed-forward signalling pathway that mediates autophagic removal of damaged mitochondria (mitophagy). With over 130 mutations identified to date in over 1000 patients with early onset parkinsonism, Parkin is considered a hot spot of signalling pathways involved in PD aetiology. Parkin is an E3 ligase and how its activity is regulated has been extensively studied: inter-domain interactions exert a tight inhibition on Parkin activity; binding to phospho-ubiquitin relieves this auto-inhibition; and phosphorylation of Parkin shifts the equilibrium towards maximal Parkin activation. This review focusses on recent, structural findings on the regulation of Parkin activity. What follows is a mechanistic introduction to the family of E3 ligases that includes Parkin, followed by a brief description of structural elements unique to Parkin that lock the enzyme in an autoinhibited state, contrasted with emerging models that have shed light on possible mechanisms of Parkin activation.