Parkin E3 ubiquitin-protein ligase (PRKN)

Parkin is a neuroprotective E3 ubiquitin-protein ligase that plays a critical role in maintaining cellular health through the ubiquitin-proteasome system and mitochondrial quality control. The protein consists of 465 amino acids organized into five distinct structural domains: an N-terminal ubiquitin-like domain (Ubl), a unique RING0 domain, followed by RING1, an in-between-RING (IBR) domain, and RING2 domains collectively forming the RING-between-RING (RBR) architecture. Structurally, Parkin adopts a compact, autoinhibited conformation stabilized by multiple hydrophobic interactions. The protein coordinates eight zinc ions through its various RING-like domains, with each zinc ion playing crucial roles in maintaining structural integrity. The RING0 domain exhibits a unique hairpin arrangement of zinc coordination, while the IBR domain forms a distinctive dual scissor-like and GAG knuckle-like zinc-binding structure that is critical for stabilizing the overall geometry and orientation of the RING domains. Parkin functions as a RING/HECT hybrid E3 ligase, combining features of both classical enzyme families. The RING1 domain serves as the binding site for E2 ubiquitin-conjugating enzymes such as UbcH7 and UbcH8, while the RING2 domain contains the catalytic machinery. The catalytic site features a cysteine residue at position 431 (Cys431) that forms a transient thioester bond with ubiquitin, along with histidine 433 (His433) and glutamate 444 (Glu444), forming a catalytic triad essential for ubiquitin transfer activity. In its basal state, Parkin is autoinhibited through multiple mechanisms. The Ubl domain and a repressor (REP) linker region physically occlude the E2 binding site on RING1, while the RING0 domain partially covers the catalytic cysteine on RING2. This autoinhibition can be relieved through phosphorylation of Serine 65 in the Ubl domain or through mutations at interdomain interfaces, both of which increase Parkin's ubiquitin ligase activity. The protein's primary biological function involves mitochondrial quality control and mitophagy. Parkin is recruited to damaged mitochondria where it is activated by PINK1 kinase, which phosphorylates both ubiquitin and Parkin itself. Once activated, Parkin ubiquitinates various mitochondrial outer membrane proteins, marking damaged mitochondria for autophagic degradation. Beyond mitochondrial substrates, Parkin can ubiquitinate several other proteins including synphilin-1, alpha-synuclein, Pael-R, synaptotagmin XI, Sept5, and the transcription factor SIM2. Mutations in Parkin are one of the most common hereditary factors in autosomal recessive juvenile Parkinsonism (AR-JP). Over 120 pathogenic mutations have been identified throughout all domains of the protein, with mutations clustering in three functional regions: zinc coordination residues affecting structural stability, the E2 binding region affecting enzyme recruitment, and the catalytic region around Cys431. Notable disease-causing mutations include T351P which causes global unfolding of the IBR domain, and R334C which causes structural rearrangement. The precise mechanism by which loss of Parkin function leads to dopaminergic neuron death remains under investigation, though the prevailing hypothesis suggests that Parkin normally helps degrade proteins that are toxic to these neurons.

Other names

ParkinPARK2E3 ubiquitin-protein ligase parkinParkin RBR E3 ubiquitin protein ligase

E3 ubiquitin ligase activity - catalyzes the transfer of ubiquitin from E2 ubiquitin-conjugating enzymes to substrate proteins. Functions through both RING domain-mediated E2 binding and HECT-like catalytic cysteine mechanism. Forms thioester intermediate with ubiquitin at catalytic cysteine residue (Cys431). Targets damaged or misfolded proteins for degradation.