scholarly journals The Dynamin-Related Gtpase, Mgm1p, Is an Intermembrane Space Protein Required for Maintenance of Fusion Competent Mitochondria

2000 ◽  
Vol 151 (2) ◽  
pp. 341-352 ◽  
Author(s):  
Edith D. Wong ◽  
Jennifer A. Wagner ◽  
Steven W. Gorsich ◽  
J. Michael McCaffery ◽  
Janet M. Shaw ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Mitochondrial Fission ◽  
Mitochondrial Fusion ◽  
Mitochondrial Outer Membrane ◽  
Mitochondrial Morphology ◽  
Temperature Sensitive ◽  
Intermembrane Space ◽  
Direct Role ◽  
Membrane Fission ◽  
Mitochondrial Intermembrane Space

Mutations in the dynamin-related GTPase, Mgm1p, have been shown to cause mitochondrial aggregation and mitochondrial DNA loss in Saccharomyces cerevisiae cells, but Mgm1p's exact role in mitochondrial maintenance is unclear. To study the primary function of MGM1, we characterized new temperature sensitive MGM1 alleles. Examination of mitochondrial morphology in mgm1 cells indicates that fragmentation of mitochondrial reticuli is the primary phenotype associated with loss of MGM1 function, with secondary aggregation of mitochondrial fragments. This mgm1 phenotype is identical to that observed in cells with a conditional mutation in FZO1, which encodes a transmembrane GTPase required for mitochondrial fusion, raising the possibility that Mgm1p is also required for fusion. Consistent with this idea, mitochondrial fusion is blocked in mgm1 cells during mating, and deletion of DNM1, which encodes a dynamin-related GTPase required for mitochondrial fission, blocks mitochondrial fragmentation in mgm1 cells. However, in contrast to fzo1 cells, deletion of DNM1 in mgm1 cells restores mitochondrial fusion during mating. This last observation indicates that despite the phenotypic similarities observed between mgm1 and fzo1 cells, MGM1 does not play a direct role in mitochondrial fusion. Although Mgm1p was recently reported to localize to the mitochondrial outer membrane, our studies indicate that Mgm1p is localized to the mitochondrial intermembrane space. Based on our localization data and Mgm1p's structural homology to dynamin, we postulate that it functions in inner membrane remodeling events. In this context, the observed mgm1 phenotypes suggest that inner and outer membrane fission is coupled and that loss of MGM1 function may stimulate Dnm1p-dependent outer membrane fission, resulting in the formation of mitochondrial fragments that are structurally incompetent for fusion.

scholarly journals Sam50-Mic19-Mic60 axis Determines Mitochondrial Cristae Architecture by Mediating Mitochondrial Outer and Inner Membrane Contact

2018 ◽  
Author(s):  
Junhui Tang ◽  
Kuan Zhang ◽  
Jun Dong ◽  
Chaojun Yan ◽  
Shi Chen ◽  
...  
Keyword(s):  
Membrane Protein ◽  
Outer Membrane ◽  
Mitochondrial Outer Membrane ◽  
Mitochondrial Morphology ◽  
Intermembrane Space ◽  
Inner Membrane ◽  
Atp Production ◽  
Mitochondrial Intermembrane Space ◽  
Membrane Contact ◽  
Inner Membrane Protein

ABSTRACTMitochondrial cristae are critical for efficient oxidative phosphorylation, however, how cristae architecture is precisely organized remains largely unknown. Here, we discovered that Mic19, a core component of MICOS (mitochondrial contact site and cristae organizing system) complex, can be cleaved at N-terminal by mitochondrial protease OMA1. Mic19 directly interacts with mitochondrial outer-membrane protein Sam50 (the key subunit of SAM complex) and inner-membrane protein Mic60 (the key component of MICOS complex) to form Sam50-Mic19-Mic60 axis, which dominantly connects SAM and MICOS complexes to assemble MIB (mitochondrial intermembrane space bridging) supercomplex for mediating mitochondrial outer- and inner-membrane contact. OMA1-mediated Mic19 cleavage causes Sam50-Mic19-Mic60 axis disruption, which separates SAM and MICOS and leads to MIB disassembly. Disrupted Sam50-Mic19-Mic60 axis, even in the presence of SAM and MICOS complexes, causes the abnormal mitochondrial morphology, loss of mitochondrial cristae junctions, abnormal cristae distribution and reduced ATP production. Importantly, Sam50 displays punctate distribution at mitochondrial outer membrane, and acts as an anchoring point to guide the formation of mitochondrial cristae junctions. Therefore, we propose a model that Sam50-Mic19-Mic60 axis mediated SAM-MICOS complexes integration determines mitochondrial cristae architecture.

scholarly journals Regulation of mitochondrial fusion by the F-box protein Mdm30 involves proteasome-independent turnover of Fzo1

2006 ◽  
Vol 173 (5) ◽  
pp. 645-650 ◽  
Author(s):  
Mafalda Escobar-Henriques ◽  
Benedikt Westermann ◽  
Thomas Langer
Keyword(s):  
Outer Membrane ◽  
Outer Membrane Proteins ◽  
Critical Role ◽  
Mitochondrial Fusion ◽  
Yeast Cells ◽  
Mitochondrial Outer Membrane ◽  
Central Component ◽  
Mitochondrial Morphology ◽  
Proteolytic Pathway ◽  
F Box Protein

Mitochondrial morphology depends on balanced fusion and fission events. A central component of the mitochondrial fusion apparatus is the conserved GTPase Fzo1 in the outer membrane of mitochondria. Mdm30, an F-box protein required for mitochondrial fusion in vegetatively growing cells, affects the cellular Fzo1 concentration in an unknown manner. We demonstrate that mitochondrial fusion requires a tight control of Fzo1 levels, which is ensured by Fzo1 turnover. Mdm30 binds to Fzo1 and, dependent on its F-box, mediates proteolysis of Fzo1. Unexpectedly, degradation occurs along a novel proteolytic pathway not involving ubiquitylation, Skp1–Cdc53–F-box (SCF) E3 ubiquitin ligase complexes, or 26S proteasomes, indicating a novel function of an F-box protein. This contrasts to the ubiquitin- and proteasome-dependent turnover of Fzo1 in α-factor–arrested yeast cells. Our results therefore reveal not only a critical role of Fzo1 degradation for mitochondrial fusion in vegetatively growing cells but also the existence of two distinct proteolytic pathways for the turnover of mitochondrial outer membrane proteins.

Abstract 393: MCL-1 Promotes Survival and Influences Mitochondrial Dynamics in Cardiac Myocytes

2015 ◽  
Vol 117 (suppl_1) ◽  
Author(s):  
Alexandra G Moyzis ◽  
Robert L Thomas ◽  
Jennifer Kuo ◽  
Åsa B Gustafsson
Keyword(s):  
Cell Death ◽  
Cardiac Myocytes ◽  
Apoptotic Cell ◽  
Mitochondrial Dynamics ◽  
Mitochondrial Fission ◽  
Apoptotic Cell Death ◽  
Mitochondrial Fusion ◽  
Mitochondrial Outer Membrane ◽  
Mitochondrial Morphology ◽  
Rapid Degradation

The BCL-2 family proteins are important regulators of mitochondrial structure and integrity. MCL-1 is an anti-apoptotic BCL-2 protein that is highly expressed in the myocardium compared to the other anti-apoptotic proteins BCL-2 and BCL-X L. Recently, we reported that MCL-1 is essential for myocardial homeostasis. Cardiac-specific deletion of MCL-1 in mice led to rapid mitochondrial dysfunction, hypertrophy, and lethal cardiomyopathy. Surprisingly, MCL-1 deficient myocytes did not undergo apoptotic cell death. Instead, the cells displayed signs of mitochondrial deterioration and necrotic cell death, suggesting that MCL-1 has an additional role in maintaining mitochondrial function in cardiac myocytes. Similarly, deletion of MCL-1 in fibroblasts caused rapid mitochondrial fragmentation followed by cell death at 72 hours. Interestingly, the MCL-1 deficient fibroblasts retained cytochrome c in the mitochondria , confirming that the cells were not undergoing apoptotic cell death. We have also identified that MCL-1 localizes to the mitochondrial outer membrane (OM) and the matrix in the myocardium and that the two forms respond differently to stress. MCL-1 OM was rapidly degraded after myocardial infarction or fasting, whereas MCL-1 Matrix levels were maintained. Similarly, starvation of MEFs resulted in rapid degradation of MCL-1 OM , whereas MCL-1 Matrix showed delayed degradation. Treatment with the mitochondrial uncoupler FCCP led to rapid degradation of both forms. This suggests that the susceptibility to degradation is dependent on its localization and the nature of the stress. Our data also suggests that these two forms perform distinct functions in regulating mitochondrial morphology and survival. Overexpression of MCL-1 Matrix promoted mitochondrial fusion in fibroblasts under baseline conditions and protected cells against FCCP-mediated mitochondrial fission and clearance by autophagosomes. Thus, our data suggest that MCL-1 exists in two separate locations where it performs different functions. MCL-1 Matrix promotes mitochondrial fusion, which protects cells against excessive mitochondrial clearance during unfavorable conditions.

scholarly journals Mdm12p, a Component Required for Mitochondrial Inheritance That Is Conserved between Budding and Fission Yeast

1997 ◽  
Vol 136 (3) ◽  
pp. 545-553 ◽  
Author(s):  
Karen H. Berger ◽  
L. Farah Sogo ◽  
Michael P. Yaffe
Keyword(s):  
Membrane Protein ◽  
Fission Yeast ◽  
Outer Membrane ◽  
Subcellular Fractionation ◽  
Biochemical Properties ◽  
Dominant Negative ◽  
Mitochondrial Outer Membrane ◽  
Mitochondrial Morphology ◽  
Temperature Sensitive ◽  
Giant Mitochondria

Saccharomyces cerevisiae cells lacking the MDM12 gene product display temperature-sensitive growth and possess abnormally large, round mitochondria that are defective for inheritance by daughter buds. Analysis of the wild-type MDM12 gene revealed its product to be a 31-kD polypeptide that is homologous to a protein of the fission yeast Schizosaccharomyces pombe. When expressed in S. cerevisiae, the S. pombe Mdm12p homolog conferred a dominant-negative phenotype of giant mitochondria and aberrant mitochondrial distribution, suggesting partial functional conservation of Mdm12p activity between budding and fission yeast. The S. cerevisiae Mdm12p was localized by indirect immunofluorescence microscopy and by subcellular fractionation and immunodetection to the mitochondrial outer membrane and displayed biochemical properties of an integral membrane protein. Mdm12p is the third mitochondrial outer membrane protein required for normal mitochondrial morphology and distribution to be identified in S. cerevisiae and the first such mitochondrial component that is conserved between two different species.

scholarly journals A novel insertion pathway of mitochondrial outer membrane proteins with multiple transmembrane segments

2007 ◽  
Vol 179 (7) ◽  
pp. 1355-1363 ◽  
Author(s):  
Hidenori Otera ◽  
Yohsuke Taira ◽  
Chika Horie ◽  
Yurina Suzuki ◽  
Hiroyuki Suzuki ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Outer Membrane Proteins ◽  
Benzodiazepine Receptor ◽  
Mitochondrial Outer Membrane ◽  
Intermembrane Space ◽  
Transmembrane Segments ◽  
Import Receptors ◽  
Mitochondrial Intermembrane Space

The central channel Tom40 of the preprotein translocase of outer membrane (TOM) complex is thought to be responsible for the import of virtually all preproteins synthesized outside the mitochondria. In this study, we analyze the topogenesis of the peripheral benzodiazepine receptor (PBR), which integrates into the mitochondrial outer membrane (MOM) through five hydrophobic transmembrane segments (TMSs) and functions in cholesterol import into the inner membrane. Analyses of in vitro and in vivo import into TOM component–depleted mitochondria reveal that PBR import (1) depends on the import receptor Tom70 but requires neither the Tom20 and Tom22 import receptors nor the import channel Tom40, (2) shares the post-Tom70 pathway with the C-tail–anchored proteins, and (3) requires factors of the mitochondrial intermembrane space. Furthermore, membrane integration of mitofusins and mitochondrial ubiquitin ligase, the MOM proteins with two and four TMSs, respectively, proceeds through the same initial pathway. These findings reveal a previously unidentified pathway of the membrane integration of MOM proteins with multiple TMSs.

scholarly journals The intramitochondrial dynamin-related GTPase, Mgm1p, is a component of a protein complex that mediates mitochondrial fusion

2003 ◽  
Vol 160 (3) ◽  
pp. 303-311 ◽  
Author(s):  
Edith D. Wong ◽  
Jennifer A. Wagner ◽  
Sidney V. Scott ◽  
Voytek Okreglak ◽  
Timothy J. Holewinske ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Mitochondrial Fission ◽  
Mitochondrial Fusion ◽  
Intermembrane Space ◽  
Inner Membrane ◽  
Self Assembling ◽  
Novel Method ◽  
Membrane Components

Abalance between fission and fusion events determines the morphology of mitochondria. In yeast, mitochondrial fission is regulated by the outer membrane–associated dynamin-related GTPase, Dnm1p. Mitochondrial fusion requires two integral outer membrane components, Fzo1p and Ugo1p. Interestingly, mutations in a second mitochondrial-associated dynamin-related GTPase, Mgm1p, produce similar phenotypes to fzo1 and ugo cells. Specifically, mutations in MGM1 cause mitochondrial fragmentation and a loss of mitochondrial DNA that are suppressed by abolishing DNM1-dependent fission. In contrast to fzo1ts mutants, blocking DNM1-dependent fission restores mitochondrial fusion in mgm1ts cells during mating. Here we show that blocking DNM1-dependent fission in Δmgm1 cells fails to restore mitochondrial fusion during mating. To examine the role of Mgm1p in mitochondrial fusion, we looked for molecular interactions with known fusion components. Immunoprecipitation experiments revealed that Mgm1p is associated with both Ugo1p and Fzo1p in mitochondria, and that Ugo1p and Fzo1p also are associated with each other. In addition, genetic analysis of specific mgm1 alleles indicates that Mgm1p's GTPase and GTPase effector domains are required for its ability to promote mitochondrial fusion and that Mgm1p self-interacts, suggesting that it functions in fusion as a self-assembling GTPase. Mgm1p's localization within mitochondria has been controversial. Using protease protection and immuno-EM, we have shown previously that Mgm1p localizes to the intermembrane space, associated with the inner membrane. To further test our conclusions, we have used a novel method using the tobacco etch virus protease and confirm that Mgm1p is present in the intermembrane space compartment in vivo. Taken together, these data suggest a model where Mgm1p functions in fusion to remodel the inner membrane and to connect the inner membrane to the outer membrane via its interactions with Ugo1p and Fzo1p, thereby helping to coordinate the behavior of the four mitochondrial membranes during fusion.

scholarly journals Redox activation of mitochondrial intermembrane space Cu,Zn-superoxide dismutase

2005 ◽  
Vol 387 (1) ◽  
pp. 203-209 ◽  
Author(s):  
Pedro IÑARREA ◽  
Hadi MOINI ◽  
Daniel RETTORI ◽  
Derick HAN ◽  
Jesús MARTÍNEZ ◽  
...  
Keyword(s):  
Superoxide Dismutase ◽  
Outer Membrane ◽  
Alkylating Agents ◽  
Liver Mitochondria ◽  
Oxidative Modification ◽  
Mitochondrial Outer Membrane ◽  
Rat Liver Mitochondria ◽  
Intermembrane Space ◽  
H2o2 Treatment ◽  
Mitochondrial Intermembrane Space

The localization of Cu,Zn-superoxide dismutase in the mitochondrial intermembrane space suggests a functional relationship with superoxide anion (O2•−) released into this compartment. The present study was aimed at examining the functionality of Cu,Zn-superoxide dismutase and elucidating the molecular basis for its activation in the intermembrane space. Intact rat liver mitochondria neither scavenged nor dismutated externally generated O2•−, unless the mitochondrial outer membrane was disrupted selectively by digitonin. The activation of the intermembrane space Cu,Zn-superoxide dismutase following the disruption of mitochondrial outer membrane was largely inhibited by bacitracin, an inhibitor of protein disulphide-isomerase. Thiol alkylating agents, such as N-methylmaleimide or iodoacetamide, decreased intermembrane space Cu,Zn-superoxide dismutase activation during, but not after, disruption of the outer membrane. This inhibitory effect was overcome by exposing mitochondria to low micromolar concentrations of H2O2 before disruption of the outer membrane in the presence of the alkylating agents. Moreover, H2O2 treatment alone enabled intact mitochondria to scavenge externally generated O2•−. These findings suggest that intermembrane space Cu,Zn-superoxide dismutase is inactive in intact mitochondria and that an oxidative modification of its critical thiol groups is necessary for its activation.

scholarly journals Role of MMM1 in Maintaining Mitochondrial Morphology inNeurospora crassa

2000 ◽  
Vol 11 (9) ◽  
pp. 2961-2971 ◽  
Author(s):  
Holger Prokisch ◽  
Walter Neupert ◽  
Benedikt Westermann
Keyword(s):  
Outer Membrane ◽  
Transmembrane Domain ◽  
Female Sterility ◽  
Mitochondrial Outer Membrane ◽  
Mitochondrial Morphology ◽  
Temperature Sensitive ◽  
Dependent Manner ◽  
Giant Mitochondria ◽  
Mitochondrial Transport ◽  
General Importance

Mmm1p is a protein required for maintenance of mitochondrial morphology in budding yeast. It was proposed that it is required to mediate the interaction of the mitochondrial outer membrane with the actin cytoskeleton. We report the cloning and characterization of MMM1 of the filamentous fungus Neurospora crassa, an organism that uses microtubules for mitochondrial transport. Mutation of themmm-1 gene leads to a temperature-sensitive slow growth phenotype and female sterility. Mutant cells harbor abnormal giant mitochondria at all stages of the asexual life cycle, whereas actin filament-depolymerizing drugs have no effect on mitochondrial morphology. The MMM1 protein has a single transmembrane domain near the N terminus and exposes a large C-terminal domain to the cytosol. The protein can be imported into the outer membrane in a receptor-dependent manner. Our findings suggest that MMM1 is a factor of general importance for mitochondrial morphology independent of the cytoskeletal system used for mitochondrial transport.

scholarly journals MMM1 encodes a mitochondrial outer membrane protein essential for establishing and maintaining the structure of yeast mitochondria.

1994 ◽  
Vol 126 (6) ◽  
pp. 1375-1391 ◽  
Author(s):  
S M Burgess ◽  
M Delannoy ◽  
R E Jensen
Keyword(s):  
Outer Membrane ◽  
Cell Function ◽  
Mitochondrial Outer Membrane ◽  
Mitochondrial Morphology ◽  
Temperature Sensitive ◽  
Restrictive Temperature ◽  
Cell Periphery ◽  
Permissive Temperature ◽  
Yeast Saccharomyces Cerevisiae ◽  
Mitochondrial Structure

In the yeast Saccharomyces cerevisiae, mitochondria are elongated organelles which form a reticulum around the cell periphery. To determine the mechanism by which mitochondrial shape is established and maintained, we screened yeast mutants for those defective in mitochondrial morphology. One of these mutants, mmm1, is temperature-sensitive for the external shape of its mitochondria. At the restrictive temperature, elongated mitochondria appear to quickly collapse into large, spherical organelles. Upon return to the permissive temperature, wild-type mitochondrial structure is restored. The morphology of other cellular organelles is not affected in mmm1 mutants, and mmm1 does not disrupt normal actin or tubulin organization. Cells disrupted in the MMM1 gene are inviable when grown on nonfermentable carbon sources and show abnormal mitochondrial morphology at all temperatures. The lethality of mmm1 mutants appears to result from the inability to segregate the aberrant-shaped mitochondria into daughter cells. Mitochondrial structure is therefore important for normal cell function. Mmm1p is located in the mitochondrial outer membrane, with a large carboxyl-terminal domain facing the cytosol. We propose that Mmm1p maintains mitochondria in an elongated shape by attaching the mitochondrion to an external framework, such as the cytoskeleton.

scholarly journals Gag3p, an Outer Membrane Protein Required for Fission of Mitochondrial Tubules

2000 ◽  
Vol 151 (2) ◽  
pp. 333-340 ◽  
Author(s):  
Peter Fekkes ◽  
Kelly A. Shepard ◽  
Michael P. Yaffe
Keyword(s):  
Outer Membrane ◽  
Mitochondrial Fission ◽  
Mitochondrial Outer Membrane ◽  
Mitochondrial Morphology ◽  
Gene Products ◽  
Mitochondrial Fragmentation ◽  
Gene Encoding ◽  
Peripheral Protein ◽  
And Function ◽  
Two Hybrid

Mitochondrial morphology and function depend on MGM1, a Saccharomyces cerevisiae gene encoding a dynamin-like protein of the mitochondrial outer membrane. Here, we show that mitochondrial fragmentation and mitochondrial genome loss caused by lesions in MGM1 are suppressed by three novel mutations, gag1, gag2, and gag3 (for glycerol-adapted growth). Cells with any of the gag mutations displayed aberrant mitochondrial morphology characterized by elongated, unbranched tubes and highly fenestrated structures. Additionally, each of the gag mutations prevented mitochondrial fragmentation caused by loss of the mitochondrial fusion factor, Fzo1p, or by treatment of cells with sodium azide. The gag1 mutation mapped to DNM1 that encodes a dynamin-related protein required for mitochondrial fission. GAG3 encodes a novel WD40-repeat protein previously found to interact with Dnm1p in a two-hybrid assay. Gag3p was localized to mitochondria where it was found to associate as a peripheral protein on the cytosolic face of the outer membrane. This association requires neither the DNM1 nor GAG2 gene products. However, the localization of Dnm1p to the mitochondrial outer membrane is substantially reduced by the gag2 mutation, but unaffected by loss of Gag3p. These results indicate that Gag3p plays a distinct role on the mitochondrial surface to mediate the fission of mitochondrial tubules.

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