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The E3 ubiquitin ligase PARKIN (encoded by PARK2) and the protein kinase PINK1 (encoded by PARK6) are mutated in autosomal-recessive juvenile Parkinsonism (AR-JP) and work together in the disposal of damaged mitochondria by mitophagy. PINK1 is stabilized on the outside of depolarized mitochondria and phosphorylates polyubiquitin as well as the PARKIN ubiquitin-like (Ubl) domain. These phosphorylation events lead to PARKIN recruitment to mitochondria, and activation by an unknown allosteric mechanism. Here we present the crystal structure of Pediculus humanus PARKIN in complex with Ser65-phosphorylated ubiquitin (phosphoUb), revealing the molecular basis for PARKIN recruitment and activation. The phosphoUb binding site on PARKIN comprises a conserved phosphate pocket and harbours residues mutated in patients with AR-JP. PhosphoUb binding leads to straightening of a helix in the RING1 domain, and the resulting conformational changes release the Ubl domain from the PARKIN core; this activates PARKIN. Moreover, phosphoUb-mediated Ubl release enhances Ubl phosphorylation by PINK1, leading to conformational changes within the Ubl domain and stabilization of an open, active conformation of PARKIN. We redefine the role of the Ubl domain not only as an inhibitory but also as an activating element that is restrained in inactive PARKIN and released by phosphoUb. Our work opens up new avenues to identify small-molecule PARKIN activators., Competing Interests: Statement DK is part of the DUB Alliance that includes Cancer Research Technology and FORMA Therapeutics, and is a consultant for FORMA Therapeutics.

Protein ubiquitination regulates many cellular processes via attachment of structurally and functionally distinct ubiquitin (Ub) chains. Several atypical chain types have remained poorly characterized because the enzymes mediating their assembly and receptors with specific binding properties have been elusive. We found that the human HECT E3 ligases UBE3C and AREL1 assemble K48/K29- and K11/K33-linked Ub chains, respectively, and can be used in combination with DUBs to generate K29- and K33-linked chains for biochemical and structural analyses. Solution studies indicate that both chains adopt open and dynamic conformations. We further show that the N-terminal Npl4-like zinc finger (NZF1) domain of the K29/K33-specific deubiquitinase TRABID specifically binds K29/K33-linked diUb, and a crystal structure of this complex explains TRABID specificity and suggests a model for chain binding by TRABID. Our work uncovers linkage-specific components in the Ub system for atypical K29- and K33-linked Ub chains, providing tools to further understand these unstudied posttranslational modifications., (Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.)

A correction to the article "Mechanism of phospho-ubiquitin-induced PARKIN activation" which was published in issue #524 is presented.