AAA proteases of mitochondria: quality control of membrane proteins and regulatory functions during mitochondrial biogenesis

Langer, Thomas; Käser, Michael; Klanner, Carola; Leonhard, Klaus

doi:10.1042/bst0290431

Cited by 95 publications

(74 citation statements)

References 3 publications

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“…Mitochondria have their own proteolytic system, two AAA protease complexes in the inner membrane, whose function is to degrade unfolded membrane proteins. 5 Cytosolic proteosomes have also been shown to mediate degradation of proteins on the inner and outer mitochondrial membrane. 6 In addition to proteolytic and proteosomal degradation, recent evidence points to a lysosomal pathway in which vesicles bud from mitochondrial tubules, sequester selected mitochondrial cargos, and then deliver those mitochondrial components to the lysosome for degradation.…”

Section: Open Questionsmentioning

confidence: 99%

The pathways of mitophagy for quality control and clearance of mitochondria

2012

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Selective autophagy of mitochondria, known as mitophagy, is an important mitochondrial quality control mechanism that eliminates damaged mitochondria. Mitophagy also mediates removal of mitochondria from developing erythrocytes, and contributes to maternal inheritance of mitochondrial DNA through the elimination of sperm-derived mitochondria. Recent studies have identified specific regulators of mitophagy that ensure selective sequestration of mitochondria as cargo. In yeast, the mitochondrial outer membrane protein autophagy-related gene 32 (ATG32) recruits the autophagic machinery to mitochondria, while mammalian Nix is required for degradation of erythrocyte mitochondria. The elimination of damaged mitochondria in mammals is mediated by a pathway comprised of PTEN-induced putative protein kinase 1 (PINK1) and the E3 ubiquitin ligase Parkin. PINK1 and Parkin accumulate on damaged mitochondria, promote their segregation from the mitochondrial network, and target these organelles for autophagic degradation in a process that requires Parkin-dependent ubiquitination of mitochondrial proteins. Here we will review recent advances in our understanding of the different pathways of mitophagy. In addition, we will discuss the relevance of these pathways in neurons where defects in mitophagy have been implicated in neurodegeneration. Facts Mitophagy mediates clearance of damaged mitochondria, and is also involved in the removal of mitochondria from maturing erythrocytes and eliminating sperm-derived mitochondria after fertilization. In yeast, the mitochondrial outer membrane protein autophagy-related gene 32 (ATG32) recruits the core autophagic machinery to mitochondria for their selective removal. A pathway containing PTEN-induced putative protein kinase 1 (PINK1) and Parkin responds to loss of mitochondrial membrane potential by targeting damaged mitochondria for clearance. The PINK1/Parkin pathway is triggered when PINK1 is stabilized on the outer membrane of damaged mitochondria, where it facilitates recruitment of cytosolic Parkin. Damaged mitochondria are prevented from moving and fusing with the mitochondrial reticulum in preparation for their mitophagic clearance. Open QuestionsHow distinct are the mitophagy pathways triggered by different stimuli or conditions?To what extent does Parkin activate mitophagy by causing the degradation of mitochondrial surface proteins or hyperubiquitinating the mitochondrial surface? How do PINK1 and Parkin interact with one another and with substrates on the mitochondrial surface in causing mitophagy? In contrast to the remarkable conservation of the core autophagic machinery, why are mitophagy-specific genes so little conserved between yeast and mammals? How best should mitophagy be triggered by researchers probing physiologically relevant pathways?The mitochondrion is an important actor in the life of a eukaryotic cell, but, like all good actors, a mitochondrion needs to exit the stage at the right time. Mitophagy removes mitochondria once they have played their part. This artic...

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Section: Open Questionsmentioning

confidence: 99%

The pathways of mitophagy for quality control and clearance of mitochondria

2012

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“…Moreover, intramembrane peptidases appear to recognize only substrates containing one transmembrane segment, whereas Oma1 was found to cleave a polytopic membrane protein. On the other hand, Oma1 can be distinguished from peptidases mediating the complete turnover of membrane proteins, like the 26 S proteasome or AAA proteases (51,52), as proteolysis by Oma1 seemingly does not depend on ATP and results in the accumulation of proteolytic fragments of a polytopic substrate protein. Oma1, together with its homologues, therefore comprises a novel class of peptidases that recognize membrane-embedded polypeptides as substrates.…”

Section: Oma1 Forms a High Molecular Mass Complex In The Innermentioning

confidence: 99%

Oma1, a Novel Membrane-bound Metallopeptidase in Mitochondria with Activities Overlapping with the m-AAA Protease

Käser

Kambacheld

Kisters‐Woike

et al. 2003

Journal of Biological Chemistry

139

147

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The integrity of the inner membrane of mitochondria is maintained by a membrane-embedded quality control system that ensures the removal of misfolded membrane proteins. Two ATP-dependent AAA proteases with catalytic sites at opposite membrane surfaces are key components of this proteolytic system. Here we describe the identification of a novel conserved metallopeptidase that exerts activities overlapping with the m-AAA protease and was therefore termed Oma1. Both peptidases are integral parts of the inner membrane and mediate the proteolytic breakdown of a misfolded derivative of the polytopic inner membrane protein Oxa1. The m-AAA protease cleaves off the matrix-exposed C-terminal domain of Oxa1 and processively degrades its transmembrane domain. In the absence of the m-AAA protease, proteolysis of Oxa1 is mediated in an ATP-independent manner by Oma1 and a yet unknown peptidase resulting in the accumulation of N-and C-terminal proteolytic fragments. Oma1 exposes its proteolytic center to the matrix side; however, mapping of Oma1 cleavage sites reveals clipping of Oxa1 in loop regions at both membrane surfaces. These results identify Oma1 as a novel component of the quality control system in the inner membrane of mitochondria. Proteins homologous to Oma1 are present in higher eukaryotic cells, eubacteria and archaebacteria, suggesting that Oma1 is the founding member of a conserved family of membrane-embedded metallopeptidases.The majority of mitochondrial proteins is nuclear encoded and synthesized at cytosolic ribosomes. Import into mitochondria is mediated by various protein translocases in the outer and inner membrane that allow the passage of preproteins only in a largely unfolded conformation (1, 2). Folding and assembly of mitochondrial proteins must therefore occur inside mitochondria. Little is known about the efficiency of this process, but it is clear that mitochondria, as other organelles, harbor a quality control system that ensures the recognition and removal of non-native polypeptides, preventing their potentially harmful accumulation within the organelle (3). Notably, a functional impairment of components of this system leads to neurodegeneration in various forms of hereditary spastic paraplegia, illustrating the importance of protein quality control for mitochondrial function (4, 5).Molecular chaperone proteins and ATP-dependent proteases present in different subcompartments of mitochondria maintain protein quality control within the organelle (3). In line with the endosymbiotic origin of mitochondria, many of these components exhibit significant homology to bacterial proteins. ATP-dependent proteases homologous to Lon proteases (6 -8) and, at least in some organisms, Clp proteases (9, 10) have been identified in the mitochondrial matrix space, whereas the inner membrane harbors two AAA proteases homologous to bacterial FtsH proteases (11). These membrane-embedded peptidases were termed m-and i-AAA proteases to indicate their different topology in the inner membrane; the m-AAA protease is activ...

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“…The concerted accumulation of COX subunits is regulated by posttranslational degradation of most unassembled Cox1 and the other highly hydrophobic core subunits (27). Recently, we along with others have proposed an additional level of regulation, namely, an assembly-controlled synthesis of Cox1 (1,2,39,56).…”

mentioning

confidence: 99%

Mss51 and Ssc1 Facilitate Translational Regulation of Cytochrome c Oxidase Biogenesis

Fontanesi¹,

Soto

Horn

et al. 2010

Molecular and Cellular Biology

122

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The intricate biogenesis of multimeric organellar enzymes of dual genetic origin entails several levels of regulation. In Saccharomyces cerevisiae, mitochondrial cytochrome c oxidase (COX) assembly is regulated translationally. Synthesis of subunit 1 (Cox1) is contingent on the availability of its assembly partners, thereby acting as a negative feedback loop that coordinates COX1 mRNA translation with Cox1 utilization during COX assembly. The COX1 mRNA-specific translational activator Mss51 plays a fundamental role in this process. Here, we report that Mss51 successively interacts with the COX1 mRNA translational apparatus, newly synthesized Cox1, and other COX assembly factors during Cox1 maturation/assembly. Notably, the mitochondrial Hsp70 chaperone Ssc1 is shown to be an Mss51 partner throughout its metabolic cycle. We conclude that Ssc1, by interacting with Mss51 and Mss51-containing complexes, plays a critical role in Cox1 biogenesis, COX assembly, and the translational regulation of these processes.

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AAA proteases of mitochondria: quality control of membrane proteins and regulatory functions during mitochondrial biogenesis

Cited by 95 publications

References 3 publications

The pathways of mitophagy for quality control and clearance of mitochondria

The pathways of mitophagy for quality control and clearance of mitochondria

Oma1, a Novel Membrane-bound Metallopeptidase in Mitochondria with Activities Overlapping with the m-AAA Protease

Mss51 and Ssc1 Facilitate Translational Regulation of Cytochrome c Oxidase Biogenesis

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