Interaction between RING1 (R1) and the Ubiquitin-like (UBL) Domains Is Critical for the Regulation of Parkin Activity

Abstract

Parkin is an E3 ligase that contains a ubiquitin-like (UBL)domain Parkinson disease (PD)3 is a neurodegenerative disorder that results from degenerated dopaminergic neurons in the substantia nigra. Most cases of PD are sporadic, and ϳ10% are familial (1). Gene mutations that are known to be responsible for the onset of the disease include PARK2 (Parkin), PARK6 (PINK1), PARK7 (DJ-1), LRRK2, and SNCA (␣-synuclein). LRRK2 and SNCA mutations are believed to cause PD through a gain of function, whereas PARK2, PARK6, and PARK7 mutations cause PD through a loss of function (2-4).Autosomal recessive early onset parkinsonism is linked to several loci, including PARK2 and PARK6 (5). The PARK2 gene encodes Parkin, an E3 ubiquitin ligase that consists of 465 amino acid residues. Parkin is composed of an ubiquitin-like (UBL) domain at the N terminus and a R1-in-between-ring (IBR)-Rind 2 (R2) motif at the C terminus (6 -8). Structurally, Parkin is a RING-type E3 ligase, but functionally it acts as a RING/HECT hybrid E3 ligase (9 -12). Parkin functions like a RING-type E3 ligase by interacting with E2 enzymes, UbcH7 and UbcH8, via the IBR domain, whereas the RING1 domain binds to substrates, allowing direct substrate ubiquitination. Parkin can also function like a HECT-type E3 ligase by catalyzing the transfer of ubiquitin from an E2 ubiquitin-conjugating enzyme to the substrates via the active-site residues, Cys-431 and His-433. E2 enzymes that support Parkin function as a HECT-type E3 ligase are UbcH7, UbcH8, and Ubc13/Uev1a heterodimer (13,14).Substrates that are ubiquitinated by active Parkin include mitofusin (Mfn) 1 and 2, dynamin-related protein 1 (Drp1), voltage-dependent anion-selective channel protein 1 (VDAC1), mitochondrial Rho GTPase (Miro), and translocase of outer membrane 20 (TOM20) (15)(16)(17)(18)(19)(20). Parkin ligates these substrates with [21][22][23]. The substrates of Parkin with Lys-48-linked polyubiquitin chains are degraded by the ubiquitin proteasome system (23-26). However, those polyubiquitinated with Lys-63 or Lys-27 ubiquitin linkage recruit ubiquitin-binding adaptors such as histone deacetylase 6 (HDAC6) and p62/SQSTM1 (21,(27)(28)(29). The stability of Mfn1 and -2 and Drp1 are reduced by 30,31). TOM20 is both mono-and polyubiquitinated by Parkin by . In the case of VDAC1, Parkin catalyzes polyubiquitination with ubiquitin Lys-27 and Lys-63 linkages, which leads to recruitment of p62/SQSTM1 and subsequent induction of mitophagy (18,32).

Mitophagy imbalance in cardiomyocyte ischaemia/reperfusion injury

“…Activated Parkin ubiquitinates OMM proteins. 26,27 The ubiquitination serves as recognition tag for LC adaptors to selectively target damaged mitochondria into mitophagosomes. The OMM translocation and activation of Parkin require PINK1.…”

PARIS induced defects in mitochondrial biogenesis drive dopamine neuron loss under conditions of parkin or PINK1 deficiency

“…Among the PD genes, the most compelling mitochondrial link exists for PTEN Induced Kinase 1 (PINK1) and parkin whose functions converge in common signaling pathways to regulate multiple domains of mitochondrial network homeostasis and quality control [4]. Besides the mitochondria, both PINK1 and parkin are localized to various other cellular compartments including the cytosol and exert neuroprotective functions [5][6][7][8][9][10][11][12][13].…”

Decision between mitophagy and apoptosis by Parkin via VDAC1 ubiquitination

“…Among the PD-associated genes mentioned above, PARK6 encodes PTEN-induced putative kinase1 (PINK1) and PARK2 encodes Parkin, which is a RING/HECT type E3 ubiquitin ligase. Parkin is phosphorylated at serine 65 located within the ubiquitinlike (UBL) domain by PINK1 and then its E3 ligase activity is activated (8,9). PINK1 is a serine/threonine kinase that is activated under mitochondrial damages.…”