Editors' ChoiceStructural Biology

The key to unlocking PARKIN

Sci. Signal.  01 Sep 2015:
Vol. 8, Issue 392, pp. ec248
DOI: 10.1126/scisignal.aad3217

The E3 ubiquitin ligase PARKIN and the kinase PINK1 interact to clear damaged mitochondria, and mutations in either result in autosomal-recessive juvenile Parkinsonism (AR-JP). PINK1 is recruited to depolarized mitochondria and phosphorylates ubiquitin and the ubiquitin-like domain (Ubl) of PARKIN. Wauer et al. investigated the molecular mechanism by which PARKIN was activated by PINK1 through phosphorylated ubiquitin (pUb). They solved the crystal structure of the complex formed between pUb and PARKIN from the body louse Pediculus humanus corporis (PhPARKIN). Key interaction sites between PARKIN and pUb identified from the structure included residues in PARKIN that are mutated in AR-JP. Autoubiquitylation assays revealed that human PARKIN (HsPARKIN) was activated by pUb. Pharmacological depolarization of mitochondria in HeLa cells led to the rapid mitochondrial localization of yellow fluorescent protein–tagged HsPARKIN, but not of tagged PARKIN mutants defective in pUb binding. Cytosolic PARKIN exists in an autoinhibited conformation in which binding to E2 Ub-conjugating enzymes is blocked by the N-terminal region of the Ubl domain and a repressor domain (REP). The structure of pUb and PhPARKN showed that binding of pUb to a helix domain called pUBH in PhPARKIN destabilized the inhibitory interactions of the REP domain and released the Ubl domain from the PARKIN core, which would enable PARKIN activation and enable PINK1 to phosphorylate the exposed Ubl domain at Ser65. Western blotting analysis with an antibody specific for PARKIN phosphorylated at Ser65 showed that PARKIN phosphorylation in vitro by PINK1 was enhanced in the presence of pUb. Nuclear magnetic resonance measurements showed that the Ubl domain underwent conformational changes when phosphorylated on Ser65, which would prevent it from interacting with the RING1 domain. These data suggest that drugs that disrupt the Ubl domain in autoinhibited PARKIN may lead to PARKIN activation and provide therapies for patients with Parkinson’s disease.

T. Wauer, M. Simicek, A. Schubert, D. Komander, Mechanism of phospho-ubiquitin-induced PARKIN activation. Nature 524, 370–374 (2015). [PubMed]