scholarly journals A nuclear-based quality control pathway for non-imported mitochondrial proteins

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Viplendra PS Shakya ◽  
William A Barbeau ◽  
Tianyao Xiao ◽  
Christina S Knutson ◽  
Max H Schuler ◽  
...  
Keyword(s):  
Quality Control ◽  
Steady State ◽  
Mitochondrial Proteins ◽  
Mitochondrial Targeting ◽  
Mitochondrial Import ◽  
Cellular Toxicity ◽  
Mitochondrial Impairment ◽  
Induced Stress ◽  
Precursor Proteins ◽  
Combined Action

Mitochondrial import deficiency causes cellular toxicity due to the accumulation of non-imported mitochondrial precursor proteins, termed mitoprotein-induced stress. Despite the burden mis-localized mitochondrial precursors place on cells, our understanding of the systems that dispose of these proteins is incomplete. Here, we cataloged the location and steady-state abundance of mitochondrial precursor proteins during mitochondrial impairment in S. cerevisiae. We found that a number of non-imported mitochondrial proteins localize to the nucleus, where they are subjected to proteasome-dependent degradation through a process we term nuclear-associated mitoprotein degradation (mitoNUC). Recognition and destruction of mitochondrial precursors by the mitoNUC pathway requires the presence of an N-terminal mitochondrial targeting sequence (MTS) and is mediated by combined action of the E3 ubiquitin ligases San1, Ubr1, and Doa10. Impaired breakdown of precursors leads to alternative sequestration in nuclear-associated foci. These results identify the nucleus as an important destination for the disposal of non-imported mitochondrial precursors.

scholarly journals The nucleus is a quality control center for non-imported mitochondrial proteins

2020 ◽  
Author(s):  
Viplendra P.S. Shakya ◽  
William A. Barbeau ◽  
Tianyao Xiao ◽  
Christina S. Knutson ◽  
Adam L. Hughes
Keyword(s):  
Quality Control ◽  
Steady State ◽  
Nuclear Protein ◽  
Protein Quality ◽  
Mitochondrial Proteins ◽  
Mitochondrial Targeting ◽  
Mitochondrial Import ◽  
Control Center ◽  
Mitochondrial Impairment ◽  
Precursor Proteins

AbstractMitochondrial import deficiency causes cellular stress due to the accumulation of non-imported mitochondrial precursor proteins. Despite the burden mis-localized mitochondrial precursors place on cells, our understanding of the systems that dispose of these proteins is incomplete. Here, we catalog the location and steady-state abundance of mitochondrial precursor proteins during mitochondrial impairment in S. cerevisiae. We find that a number of non-imported mitochondrial proteins localize to the nucleus, where they are eliminated by proteasome-based nuclear protein quality control. Recognition of mitochondrial precursors by the nuclear quality control machinery requires the presence of an N-terminal mitochondrial targeting sequence (MTS), and impaired breakdown of precursors leads to their buildup in nuclear-associated foci. These results identify the nucleus as a key destination for the disposal of non-imported mitochondrial precursors.

scholarly journals The GET pathway safeguards against non-imported mitochondrial protein stress

2020 ◽  
Author(s):  
Tianyao Xiao ◽  
Viplendra P.S. Shakya ◽  
Adam L. Hughes
Keyword(s):  
Endoplasmic Reticulum ◽  
Mitochondrial Protein ◽  
Transmembrane Proteins ◽  
Mitochondrial Proteins ◽  
Mitochondrial Import ◽  
Cellular Toxicity ◽  
Precursor Proteins ◽  
Dependent Protein ◽  
Er Targeting ◽  
Get Complex

SUMMARYDeficiencies in mitochondrial import cause the toxic accumulation of non-imported mitochondrial precursor proteins. Numerous fates for non-imported mitochondrial precursors have been identified, including proteasomal destruction, deposition into protein aggregates, and mis-targeting to other organelles. Amongst organelles, the endoplasmic reticulum (ER) has emerged as a key destination for non-imported mitochondrial proteins, but how ER-targeting of these proteins is achieved remains unclear. Here, we show that the guided entry of tail-anchored proteins (GET) complex is required for ER-targeting of endogenous mitochondrial multi-transmembrane proteins. Without a functional GET pathway, non-imported mitochondrial proteins destined for the ER are alternatively sequestered into Hsp42-dependent protein foci. The ER targeting of non-imported mitochondrial proteins by the GET complex prevents cellular toxicity and facilitates re-import of mitochondrial proteins from the ER via the recently identified ER-SURF pathway. Overall, this study outlines an important and unconventional role for the GET complex in mitigating stress associated with non-imported mitochondrial proteins.

scholarly journals The intermembrane space protein Mix23 is a novel stress-induced mitochondrial import factor

2020 ◽  
Vol 295 (43) ◽  
pp. 14686-14697 ◽  
Author(s):  
Eva Zöller ◽  
Janina Laborenz ◽  
Lena Krämer ◽  
Felix Boos ◽  
Markus Räschle ◽  
...  
Keyword(s):  
Protein Import ◽  
Mitochondrial Protein ◽  
Mitochondrial Proteins ◽  
Temperature Sensitive ◽  
Intermembrane Space ◽  
Mitochondrial Import ◽  
Induced Stress ◽  
Evolutionarily Conserved ◽  
Precursor Proteins ◽  
Biogenesis Of Mitochondria

The biogenesis of mitochondria requires the import of hundreds of precursor proteins. These proteins are transported post-translationally with the help of chaperones, meaning that the overproduction of mitochondrial proteins or the limited availability of chaperones can lead to the accumulation of cytosolic precursor proteins. This imposes a severe challenge to cytosolic proteostasis and triggers a specific transcription program called the mitoprotein-induced stress response, which activates the proteasome system. This coincides with the repression of mitochondrial proteins, including many proteins of the intermembrane space. In contrast, herein we report that the so-far-uncharacterized intermembrane space protein Mix23 is considerably up-regulated when mitochondrial import is perturbed. Mix23 is evolutionarily conserved and a homolog of the human protein CCDC58. We found that, like the subunits of the proteasome, Mix23 is under control of the transcription factor Rpn4. It is imported into mitochondria by the mitochondrial disulfide relay. Mix23 is critical for the efficient import of proteins into the mitochondrial matrix, particularly if the function of the translocase of the inner membrane 23 is compromised such as in temperature-sensitive mutants of Tim17. Our observations identify Mix23 as a novel regulator or stabilizer of the mitochondrial protein import machinery that is specifically up-regulated upon mitoprotein-induced stress conditions.

scholarly journals Coordinated Translocation of Presequence-Containing Precursor Proteins Across Two Mitochondrial Membranes: Knowns and Unknowns of How TOM and TIM23 Complexes Cooperate With Each Other

2022 ◽  
Vol 12 ◽  
Author(s):  
Marcel G. Genge ◽  
Dejana Mokranjac
Keyword(s):  
Protein Interactions ◽  
Nuclear Genome ◽  
Hydrophobic Surface ◽  
Mitochondrial Proteins ◽  
Intermembrane Space ◽  
Mitochondrial Targeting ◽  
Mitochondrial Membranes ◽  
Inner Mitochondrial Membrane ◽  
Precursor Proteins ◽  
Targeting Signals

The vast majority of mitochondrial proteins are encoded in the nuclear genome and synthesized on cytosolic ribosomes as precursor proteins with specific mitochondrial targeting signals. Mitochondrial targeting signals are very diverse, however, about 70% of mitochondrial proteins carry cleavable, N-terminal extensions called presequences. These amphipathic helices with one positively charged and one hydrophobic surface target proteins to the mitochondrial matrix with the help of the TOM and TIM23 complexes in the outer and inner membranes, respectively. Translocation of proteins across the two mitochondrial membranes does not take place independently of each other. Rather, in the intermembrane space, where the two complexes meet, components of the TOM and TIM23 complexes form an intricate network of protein–protein interactions that mediates initially transfer of presequences and then of the entire precursor proteins from the outer to the inner mitochondrial membrane. In this Mini Review, we summarize our current understanding of how the TOM and TIM23 complexes cooperate with each other and highlight some of the future challenges and unresolved questions in the field.

scholarly journals The mitochondrial surface receptor Tom70 protects the cytosol against mitoprotein-induced stress

2020 ◽  
Author(s):  
Sandra Backes ◽  
Yury S. Bykov ◽  
Markus Räschle ◽  
Jialin Zhou ◽  
Svenja Lenhard ◽  
...  
Keyword(s):  
Mitochondrial Membrane ◽  
Surface Protein ◽  
Mitochondrial Proteins ◽  
Outer Mitochondrial Membrane ◽  
Induced Stress ◽  
Precursor Proteins ◽  
Surface Receptor ◽  
Chaperone Binding

SummaryMost mitochondrial proteins are synthesized as precursors in the cytosol and post-translationally transported into mitochondria. The mitochondrial surface protein Tom70 acts at the interface of the cytosol and mitochondria. In vitro import experiments identified Tom70 as targeting receptor, particularly for hydrophobic carriers. Using in vivo methods and high content screens, we revisited the question of Tom70 function and considerably expanded the set of Tom70-dependent mitochondrial proteins. We demonstrate that the crucial activity of Tom70 is its ability to recruit cytosolic chaperones to the outer membrane. Indeed, tethering an unrelated chaperone-binding domain onto the mitochondrial surface complements most of the defects caused by Tom70 deletion. Tom70-mediated chaperone recruitment reduces the proteotoxicity of mitochondrial precursor proteins, in particular of hydrophobic inner membrane proteins. Thus, our work suggests that the predominant function of Tom70 is to tether cytosolic chaperones to the outer mitochondrial membrane, rather than to serve as a mitochondria-specifying targeting receptor.

scholarly journals Import of a major mitochondrial enzyme depends on synergy between two distinct helices of its presequence

2016 ◽  
Vol 473 (18) ◽  
pp. 2813-2829 ◽  
Author(s):  
Ester Kalef-Ezra ◽  
Dimitra Kotzamani ◽  
Ioannis Zaganas ◽  
Nitsa Katrakili ◽  
Andreas Plaitakis ◽  
...  
Keyword(s):  
Matrix Proteins ◽  
Mitochondrial Proteins ◽  
Mitochondrial Enzyme ◽  
Yeast Mitochondria ◽  
Mitochondrial Targeting ◽  
Mitochondrial Import ◽  
Transport Efficiency ◽  
Isolated Mitochondria ◽  
Intervening Sequences ◽  
Positively Charged

Mammalian glutamate dehydrogenase (GDH), a nuclear-encoded enzyme central to cellular metabolism, is among the most abundant mitochondrial proteins (constituting up to 10% of matrix proteins). To attain such high levels, GDH depends on very efficient mitochondrial targeting that, for human isoenzymes hGDH1 and hGDH2, is mediated by an unusually long cleavable presequence (N53). Here, we studied the mitochondrial transport of these proteins using isolated yeast mitochondria and human cell lines. We found that both hGDHs were very rapidly imported and processed in isolated mitochondria, with their presequences (N53) alone being capable of directing non-mitochondrial proteins into mitochondria. These presequences were predicted to form two α helices (α1: N 1–10; α2: N 16–32) separated by loops. Selective deletion of the α1 helix abolished the mitochondrial import of hGDHs. While the α1 helix alone had a very weak hGDH mitochondrial import capacity, it could direct efficiently non-mitochondrial proteins into mitochondria. In contrast, the α2 helix had no autonomous mitochondrial-targeting capacity. A peptide consisting of α1 and α2 helices without intervening sequences had GDH transport efficiency comparable with that of N53. Mutagenesis of the cleavage site blocked the intra-mitochondrial processing of hGDHs, but did not affect their mitochondrial import. Replacement of all three positively charged N-terminal residues (Arg3, Lys7 and Arg13) by Ala abolished import. We conclude that the synergistic interaction of helices α1 and α2 is crucial for the highly efficient import of hGDHs into mitochondria.

scholarly journals ER-SURF: Riding the Endoplasmic Reticulum Surface to Mitochondria

2021 ◽  
Vol 22 (17) ◽  
pp. 9655
Author(s):  
Christian Koch ◽  
Maya Schuldiner ◽  
Johannes M. Herrmann
Keyword(s):  
Quality Control ◽  
Endoplasmic Reticulum ◽  
Mitochondrial Membrane ◽  
Current Knowledge ◽  
Active Role ◽  
Mitochondrial Proteins ◽  
Receptor Proteins ◽  
Precursor Proteins ◽  
Surf Riding ◽  
Mitochondrial Membrane Protein

Most mitochondrial proteins are synthesized in the cytosol and targeted to the mitochondrial surface in a post-translational manner. The surface of the endoplasmic reticulum (ER) plays an active role in this targeting reaction. ER-associated chaperones interact with certain mitochondrial membrane protein precursors and transfer them onto receptor proteins of the mitochondrial surface in a process termed ER-SURF. ATP-driven proteins in the membranes of mitochondria (Msp1, ATAD1) and the ER (Spf1, P5A-ATPase) serve as extractors for the removal of mislocalized proteins. If the re-routing to mitochondria fails, precursors can be degraded by ER or mitochondria-associated degradation (ERAD or MAD respectively) in a proteasome-mediated reaction. This review summarizes the current knowledge about the cooperation of the ER and mitochondria in the targeting and quality control of mitochondrial precursor proteins.

The Research of Production Process Statistical Steady-State Based on the Hypothesis Test

2011 ◽  
Vol 314-316 ◽  
pp. 2433-2438
Author(s):  
Wei Zhi Wang
Keyword(s):  
Quality Control ◽  
Steady State ◽  
Production Process ◽  
Quantitative Method ◽  
Large Scale ◽  
Hypothesis Test ◽  
Influence Factors ◽  
Normal Operation ◽  
Scale Production ◽  
Large Scale Production

By only applying a after the event exam in the quality control of the batch production is not enough to meet the needs of modern large-scale production. To a certain extent, modern quality control is a dynamic process of the steady-state judge and adjustment. A simple and reliable steady-state judge rule and method is the premise to guarantee the normal operation. This paper provides a quantitative method to evaluate production process steady-state by analyzing influence factors based on mathematical statistics. The method is both suitable for simple production process and complex production process with sub-processes.

scholarly journals The mitochondrial import protein Mim1 promotes biogenesis of multispanning outer membrane proteins

2011 ◽  
Vol 194 (3) ◽  
pp. 387-395 ◽  
Author(s):  
Thomas Becker ◽  
Lena-Sophie Wenz ◽  
Vivien Krüger ◽  
Waltraut Lehmann ◽  
Judith M. Müller ◽  
...  
Keyword(s):  
Membrane Proteins ◽  
Outer Membrane ◽  
Outer Membrane Proteins ◽  
Mitochondrial Outer Membrane ◽  
Limited Information ◽  
Mitochondrial Import ◽  
Transmembrane Segments ◽  
Membrane Complex ◽  
Complex Functions ◽  
Precursor Proteins

The mitochondrial outer membrane contains translocase complexes for the import of precursor proteins. The translocase of the outer membrane complex functions as a general preprotein entry gate, whereas the sorting and assembly machinery complex mediates membrane insertion of β-barrel proteins of the outer membrane. Several α-helical outer membrane proteins are known to carry multiple transmembrane segments; however, only limited information is available on the biogenesis of these proteins. We report that mitochondria lacking the mitochondrial import protein 1 (Mim1) are impaired in the biogenesis of multispanning outer membrane proteins, whereas overexpression of Mim1 stimulates their import. The Mim1 complex cooperates with the receptor Tom70 in binding of precursor proteins and promotes their insertion and assembly into the outer membrane. We conclude that the Mim1 complex plays a central role in the import of α-helical outer membrane proteins with multiple transmembrane segments.

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