Defective mitochondrial quality control is shown to be a mechanism for neurodegeneration in some forms of Parkinson's disease.
PINK1 (PTEN induced putative kinase 1) and PARKIN (also known as PARK2) have been identified as the causal genes responsible for hereditary recessive early-onset Parkinsonism. PINK1 is a Ser/Thr kinase that specifically accumulates on depolarized mitochondria, whereas parkin is an E3 ubiquitin ligase that catalyses ubiquitin transfer to mitochondrial substrates. PINK1 acts as an upstream factor for parkin and is essential both for the activation of latent E3 parkin activity and for recruiting parkin onto depolarized mitochondria. Recently, mechanistic insights into mitochondrial quality control mediated by PINK1 and parkin have been revealed, and PINK1-dependent phosphorylation of parkin has been reported. However, the requirement of PINK1 for parkin activation was not bypassed by phosphomimetic parkin mutation, and how PINK1 accelerates the E3 activity of parkin on damaged mitochondria is still obscure. Here we report that ubiquitin is the genuine substrate of PINK1. PINK1 phosphorylated ubiquitin at Ser 65 both in vitro and in cells, and a Ser 65 phosphopeptide derived from endogenous ubiquitin was only detected in cells in the presence of PINK1 and following a decrease in mitochondrial membrane potential. Unexpectedly, phosphomimetic ubiquitin bypassed PINK1-dependent activation of a phosphomimetic parkin mutant in cells. Furthermore, phosphomimetic ubiquitin accelerates discharge of the thioester conjugate formed by UBCH7 (also known as UBE2L3) and ubiquitin (UBCH7∼ubiquitin) in the presence of parkin in vitro, indicating that it acts allosterically. The phosphorylation-dependent interaction between ubiquitin and parkin suggests that phosphorylated ubiquitin unlocks autoinhibition of the catalytic cysteine. Our results show that PINK1-dependent phosphorylation of both parkin and ubiquitin is sufficient for full activation of parkin E3 activity. These findings demonstrate that phosphorylated ubiquitin is a parkin activator.
Dynamic membrane repair and remodelling is an elemental process that maintains cell integrity and mediates efficient cellular function. Here we report that MG53, a muscle-specific tripartite motif family protein (TRIM72), is a component of the sarcolemmal membrane-repair machinery. MG53 interacts with phosphatidylserine to associate with intracellular vesicles that traffic to and fuse with sarcolemmal membranes. Mice null for MG53 show progressive myopathy and reduced exercise capability, associated with defective membrane-repair capacity. Injury of the sarcolemmal membrane leads to entry of the extracellular oxidative environment and MG53 oligomerization, resulting in recruitment of MG53-containing vesicles to the injury site. After vesicle translocation, entry of extracellular Ca 2+ facilitates vesicle fusion to reseal the membrane. Our data indicate that intracellular vesicle translocation and Ca 2+ -dependent membrane fusion are distinct steps involved in the repair of membrane damage and that MG53 may initiate the assembly of the membrane repair machinery in an oxidation-dependent manner.To maintain cellular homeostasis, eukaryotic cells must conserve the integrity of their plasma membrane through active recycling and repair in response to various sources of damage 1 . Defects in the intrinsic membrane repair response have been linked to numerous disease states, including muscular dystrophy, heart failure and neurodegeneration [2][3][4][5] . Repair of plasma membrane damage requires recruitment of intracellular vesicles to injury sites 6,7 . One protein that has been linked to membrane repair in skeletal muscle is dysferlin [8][9][10] , which is thought to act as a fusogen that participates in restoration of sarcolemmal membrane integrity following muscle injury. Evidence for this role of dysferlin comes, in part, from studies showing that ablation of dysferlin in mice results in muscular dystrophy 8 .Repair of damage to the plasma membrane is an active and dynamic process that requires several steps, including participation of molecular sensor(s) that can detect acute injury to 6 Correspondence should be addressed to J.M. or H.T. (maj2@umdnj.edu; takeshim@pharm.kyoto-u.ac.jp).Note: Supplementary Information is available on the Nature Cell Biology website. COMPETING FINANCIAL INTERESTSThe authors declare no competing financial interests. NIH Public Access Author ManuscriptNat Cell Biol. Author manuscript; available in PMC 2010 November 23. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript the plasma membrane, nucleation of intracellular vesicles at the injury site and vesicle fusion to enable membrane patch formation. It is well demonstrated that entry of extracellular Ca 2+ is involved in the fusion of intracellular vesicles to reseal the injured plasma membrane 6,11,12 , whereas the molecular machinery involved in sensing the damaged membrane signal and the nucleation process for repair-patch formation have not been fully resolved.We have previously established an immunopr...
The xeroderma pigmentosum group C (XPC) protein complex plays a key role in recognizing DNA damage throughout the genome for mammalian nucleotide excision repair (NER). Ultraviolet light (UV)-damaged DNA binding protein (UV-DDB) is another complex that appears to be involved in the recognition of NER-inducing damage, although the precise role it plays and its relationship to XPC remain to be elucidated. Here we show that XPC undergoes reversible ubiquitylation upon UV irradiation of cells and that this depends on the presence of functional UV-DDB activity. XPC and UV-DDB were demonstrated to interact physically, and both are polyubiquitylated by the recombinant UV-DDB-ubiquitin ligase complex. The polyubiquitylation altered the DNA binding properties of XPC and UV-DDB and appeared to be required for cell-free NER of UV-induced (6-4) photoproducts specifically when UV-DDB was bound to the lesion. Our results strongly suggest that ubiquitylation plays a critical role in the transfer of the UV-induced lesion from UV-DDB to XPC.
Degradation of mitochondria via a selective form of autophagy, named mitophagy, is a fundamental mechanism conserved from yeast to humans that regulates mitochondrial quality and quantity control. Mitophagy is promoted via specific mitochondrial outer membrane receptors, or ubiquitin molecules conjugated to proteins on the mitochondrial surface leading to the formation of autophagosomes surrounding mitochondria. Mitophagy-mediated elimination of mitochondria plays an important role in many processes including early embryonic development, cell differentiation, inflammation, and apoptosis. Recent advances in analyzing mitophagy in vivo also reveal high rates of steady-state mitochondrial turnover in diverse cell types, highlighting the intracellular housekeeping role of mitophagy. Defects in mitophagy are associated with various pathological conditions such as neurodegeneration, heart failure, cancer, and aging, further underscoring the biological relevance. Here, we review our current molecular understanding of mitophagy, and its physiological implications, and discuss how multiple mitophagy pathways coordinately modulate mitochondrial fitness and populations.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.