Mutations in the PARK2 (parkin) gene are responsible for an autosomal recessive form of Parkinson's disease. The parkin protein is a RING-in-between-RING E3 ubiquitin ligase that exhibits low basal activity. We describe the crystal structure of full-length rat parkin. The structure shows parkin in an autoinhibited state and provides insight into how it is activated. RING0 occludes the ubiquitin acceptor site Cys(431) in RING2, whereas a repressor element of parkin binds RING1 and blocks its E2-binding site. Mutations that disrupted these inhibitory interactions activated parkin both in vitro and in cells. Parkin is neuroprotective, and these findings may provide a structural and mechanistic framework for enhancing parkin activity.

Mutations in Parkin and PINK1 cause an inherited early-onset form of Parkinson's disease. The two proteins function together in a mitochondrial quality control pathway whereby PINK1 accumulates on damaged mitochondria and activates Parkin to induce mitophagy. How PINK1 kinase activity releases the auto-inhibited ubiquitin ligase activity of Parkin remains unclear. Here, we identify a binding switch between phospho-ubiquitin (pUb) and the ubiquitin-like domain (Ubl) of Parkin as a key element. By mutagenesis and SAXS, we show that pUb binds to RING1 of Parkin at a site formed by His302 and Arg305. pUb binding promotes disengagement of the Ubl from RING1 and subsequent Parkin phosphorylation. A crystal structure of Parkin Δ86–130 at 2.54 Å resolution allowed the design of mutations that specifically release the Ubl domain from RING1. These mutations mimic pUb binding and promote Parkin phosphorylation. Measurements of the E2 ubiquitin-conjugating enzyme UbcH7 binding to Parkin and Parkin E3 ligase activity suggest that Parkin phosphorylation regulates E3 ligase activity downstream of pUb binding.

Mutations in the ubiquitin ligase parkin are responsible for a familial form of Parkinson's disease. Parkin and the PINK1 kinase regulate a quality-control system for mitochondria. PINK1 phosphorylates ubiquitin on the outer membrane of damaged mitochondria, thus leading to recruitment and activation of parkin via phosphorylation of its ubiquitin-like (Ubl) domain. Here, we describe the mechanism of parkin activation by phosphorylation. The crystal structure of phosphorylated Bactrocera dorsalis (oriental fruit fly) parkin in complex with phosphorylated ubiquitin and an E2 ubiquitin-conjugating enzyme reveals that the key activating step is movement of the Ubl domain and release of the catalytic RING2 domain. Hydrogen/deuterium exchange and NMR experiments with the various intermediates in the activation pathway confirm and extend the interpretation of the crystal structure to mammalian parkin. Our results rationalize previously unexplained Parkinson's disease mutations and the presence of internal linkers that allow large domain movements in parkin.

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