Showing papers on "Mitochondrial carrier published in 2004"
TL;DR: The mitochondrial outer membrane is not just a barrier but a site of regulation of mitochondrial function, which includes total blockage of the flux of anionic metabolites leading to permeabilization of the outer membrane to small proteins followed by apoptotic cell death.
Abstract: The mitochondrial outer membrane is not just a barrier but a site of regulation of mitochondrial function. The VDAC family of proteins are the major pathways for metabolite flux through the outer membrane. These can be regulated in a variety of ways and the integration of these regulatory inputs allows mitochondrial metabolism to be adjusted to changing cellular conditions. This includes total blockage of the flux of anionic metabolites leading to permeabilization of the outer membrane to small proteins followed by apoptotic cell death.
475 citations
TL;DR: The binding of small Tim proteins to Mia40 is crucial for their transport across the outer membrane and represents an initial step in their assembly into IMS complexes.
Abstract: Mitochondria import nuclear-encoded precursor proteins to four different subcompartments. Specific import machineries have been identified that direct the precursor proteins to the mitochondrial outer membrane, inner membrane or matrix, respectively. However, a machinery dedicated to the import of mitochondrial intermembrane space (IMS) proteins has not been found so far. We have identified the essential IMS protein Mia40 (encoded by the Saccharomyces cerevisiae open reading frame YKL195w). Mitochondria with a mutant form of Mia40 are selectively inhibited in the import of several small IMS proteins, including the essential proteins Tim9 and Tim10. The import of proteins to the other mitochondrial subcompartments does not depend on functional Mia40. The binding of small Tim proteins to Mia40 is crucial for their transport across the outer membrane and represents an initial step in their assembly into IMS complexes. We conclude that Mia40 is a central component of the protein import and assembly machinery of the mitochondrial IMS.
442 citations
TL;DR: The events that occur during the fusion of double-membraned mitochondria are unknown and as an essential step toward determining the mechanism of mitochondrial fusion, this event in vitro is captured.
Abstract: The events that occur during the fusion of double-membraned mitochondria are unknown. As an essential step toward determining the mechanism of mitochondrial fusion, we have captured this event in vitro. Mitochondrial outer and inner membrane fusion events were separable and mechanistically distinct, but both required guanosine 5'-triphosphate hydrolysis. Homotypic trans interactions of the ancient outer transmembrane guanosine triphosphatase, Fzo1, were required to promote the fusion of mitochondrial outer membranes, whereas electrical potential was also required for fusion of inner membranes. Our conclusions provide fundamental insights into the molecular events driving mitochondrial fusion and advance our understanding of the evolution of mitochondrial fusion in eukaryotic cells.
424 citations
TL;DR: Together, these data are the first to identify a function for Sumo1 on the mitochondria and suggest a novel role for the participation ofSumo1 in mitochondrial fission.
367 citations
TL;DR: Members of the Omp85 protein family are found in eukaryotes ranging from plants to humans and are essential for cell viability in yeast and conditional omp85 mutants have defects that arise from compromised insertion of integral proteins.
Abstract: Integral proteins in the outer membrane of mitochondria control all aspects of organelle biogenesis, being required for protein import, mitochondrial fission, and, in metazoans, mitochondrial aspects of programmed cell death. How these integral proteins are assembled in the outer membrane had been unclear. In bacteria, Omp85 is an essential component of the protein insertion machinery, and we show that members of the Omp85 protein family are also found in eukaryotes ranging from plants to humans. In eukaryotes, Omp85 is present in the mitochondrial outer membrane. The gene encoding Omp85 is essential for cell viability in yeast, and conditional omp85 mutants have defects that arise from compromised insertion of integral proteins like voltage-dependent anion channel (VDAC) and components of the translocase in the outer membrane of mitochondria (TOM) complex into the mitochondrial outer membrane.
361 citations
TL;DR: Human Fis1 is characterized and results indicate that the levels of hFis1 at the mitochondrial surface influences mitochondrial fission events and hence overall mitochondrial morphology within the cell.
Abstract: Mitochondria undergo balanced fission and fusion events that enable their appropriate networking within the cell. In yeast, three factors have been identified that co-ordinate fission events at the mitochondrial outer membrane. Fis1p acts as the outer membrane receptor for recruitment of the dynamin member, Dnm1p and the WD40-repeat-containing protein Mdv1p. In mammals, the Dnm1p counterpart Drp1 has been characterized, but other components have not. Here, we report the characterization of human Fis1 (hFis1). hFis1 is inserted into the mitochondrial outer membrane via a C-terminal transmembrane domain that, along with a short basic segment, is essential for its targeting. Although expression of hFis1 does not complement the phenotype of yeast cells lacking Fis1p, overexpression of hFis1 in tissue culture cells nevertheless causes mitochondrial fragmentation and aggregation. This aggregation could be suppressed by expressing a dominant-negative Drp1 mutant (Drp1 K38A ). Knockdown of hFis1 in COS-7 cells using RNA interference results in mitochondrial morphology defects with notable extensions in the length of mitochondrial tubules. These results indicate that the levels of hFis1 at the mitochondrial surface influences mitochondrial fission events and hence overall mitochondrial morphology within the cell.
328 citations
TL;DR: It is concluded that Mdm10 plays a specific role in the biogenesis of the TOM complex, indicating a connection between the mitochondrial protein assembly apparatus and the machinery for maintenance of mitochondrial morphology.
269 citations
TL;DR: The data show that a novel pathway, to which the authors refer as alternative topogenesis, represents a key regulatory mechanism ensuring the balanced formation of both Mgm1 isoforms and through this process the mitochondrial ATP level might control mitochondrial morphology.
Abstract: Mitochondrial morphology and inheritance of mitochondrial DNA in yeast depend on the dynamin-like GTPase Mgm1. It is present in two isoforms in the intermembrane space of mitochondria both of which are required for Mgm1 function. Limited proteolysis of the large isoform by the mitochondrial rhomboid protease Pcp1/Rbd1 generates the short isoform of Mgm1 but how this is regulated is unclear. We show that near its NH2 terminus Mgm1 contains two conserved hydrophobic segments of which the more COOH-terminal one is cleaved by Pcp1. Changing the hydrophobicity of the NH2-terminal segment modulated the ratio of the isoforms and led to fragmentation of mitochondria. Formation of the short isoform of Mgm1 and mitochondrial morphology further depend on a functional protein import motor and on the ATP level in the matrix. Our data show that a novel pathway, to which we refer as alternative topogenesis, represents a key regulatory mechanism ensuring the balanced formation of both Mgm1 isoforms. Through this process the mitochondrial ATP level might control mitochondrial morphology.
229 citations
TL;DR: A recently discovered sorting and assembly machinery (SAM complex) is essential for integration and assembly of outer-membrane proteins, revealing unexpected connections to mitochondrial evolution and morphology.
Abstract: The general preprotein translocase of the outer mitochondrial membrane (TOM complex) transports virtually all mitochondrial precursor proteins, but cannot assemble outer-membrane precursors into functional complexes. A recently discovered sorting and assembly machinery (SAM complex) is essential for integration and assembly of outer-membrane proteins, revealing unexpected connections to mitochondrial evolution and morphology.
216 citations
TL;DR: The in silico analysis of the complete Arabidopsis genome has revealed almost 60 genes encoding putative members of the mitochondrial carrier family, crucial for obtaining an integrated view of mitochondrial function in plant cell metabolism.
185 citations
TL;DR: It is shown that the cytoplasmic domain of Ugo1p directly interacts with Fzo1p, whereas its intermembrane space domain binds to Mgm1p and thereby link these two GTPases during mitochondrial fusion.
TL;DR: It is proposed that the biogenesis pathway of β-barrel proteins of the outer mitochondrial membrane not only requires TOM and SAM components, but also involves components of the intermembrane space.
TL;DR: Because phosphate recycles via the phosphate carrier in mitochondria, the three isoforms of the ATP-Mg/Pi carrier are most likely responsible for the net uptake or efflux of adenine nucleotides into or from the mitochondria and hence for the variation in the matrix adanine nucleotide content, which has been found to change in many physiopathological situations.
TL;DR: The isolated tim8 and tim13 mutants in Neurospora crassa are isolated and it is shown that mitochondria lacking the Tim8-Tim13 complex were deficient in the import of the outer membrane β-barrel proteins Tom40 and porin.
TL;DR: The location of the core protein in the outer mitochondrial membrane suggests that it could modulate apoptosis or lipid transfer, both of which are associated with this subcellular compartment, during HCV infection.
Abstract: The hepatitis C virus (HCV) core protein represents the first 191 amino acids of the viral precursor polyprotein and is cotranslationally inserted into the membrane of the endoplasmic reticulum (ER). Processing at position 179 by a recently identified intramembrane signal peptide peptidase leads to the generation and potential cytosolic release of a 179-amino-acid matured form of the core protein. Using confocal microscopy, we observed that a fraction of the mature core protein colocalized with mitochondrial markers in core-expressing HeLa cells and in Huh-7 cells containing the full-length HCV replicon. Subcellular fractionation confirmed this observation and showed that the core protein associates with purified mitochondrial fractions devoid of ER contaminants. The core protein also fractionated with mitochondrion-associated membranes, a site of physical contact between the ER and mitochondria. Using immunoelectron microscopy and in vitro mitochondrial import assays, we showed that the core protein is located on the mitochondrial outer membrane. A stretch of 10 amino acids within the hydrophobic C terminus of the processed core protein conferred mitochondrial localization when it was fused to green fluorescent protein. The location of the core protein in the outer mitochondrial membrane suggests that it could modulate apoptosis or lipid transfer, both of which are associated with this subcellular compartment, during HCV infection.
TL;DR: Interactions of Bid with mitochondrial cardiolipin at the contact site can contribute significantly to its functions, according to the findings of this study.
Abstract: Release of cytochrome c from the mitochondrial intermembrane space is critical to apoptosis induced by a variety of death stimuli. Bid is a BH3-only prodeath Bcl-2 family protein that can potently activate this efflux. In the current study, we investigated the mitochondrial localization of Bid and its interactions with mitochondrial phospholipids, focusing on their relationships with Bid-induced cytochrome c release. We found that Bid binding to the mitochondria required only three of its eight helical structures (α4-α6), but not the BH3 domain, and the binding could not be inhibited by the antideath molecule Bcl-xL. Membrane fractionations indicated that tBid bound to mitochondrial outer membranes at both contact and noncontact sites. Bid could interact with specific cardiolipin species on intact mitochondria as identified by mass spectrometry. Like the binding to the mitochondria, this interaction could not be blocked by the mutation in the BH3 domain or by Bcl-xL. However, a cardiolipin-specific dye, 10-N-nonyl acridine orange, could preferentially suppress Bid binding to the mitochondrial contact site and inhibit Bid-induced mitochondrial cristae reorganization and cytochrome c release. These findings thus suggest that interactions of Bid with mitochondrial cardiolipin at the contact site can contribute significantly to its functions.
TL;DR: Two novel mitochondrial outer membrane proteins in yeast, Tom13 and Tom38/Sam35, are reported that mediate assembly of mitochondrial β-barrel proteins, Tom40, and/or porin in the outer membrane.
Abstract: Mitochondrial outer and inner membranes contain translocators that achieve protein translocation across and/or insertion into the membranes. Recent evidence has shown that mitochondrial β-barrel protein assembly in the outer membrane requires specific translocator proteins in addition to the components of the general translocator complex in the outer membrane, the TOM40 complex. Here we report two novel mitochondrial outer membrane proteins in yeast, Tom13 and Tom38/Sam35, that mediate assembly of mitochondrial β-barrel proteins, Tom40, and/or porin in the outer membrane. Depletion of Tom13 or Tom38/Sam35 affects assembly pathways of the β-barrel proteins differently, suggesting that they mediate different steps of the complex assembly processes of β-barrel proteins in the outer membrane.
TL;DR: The projection structure of the yeast ADP/ATP carrier by electron crystallography shows that carriers could form homo‐dimers in the membrane, inconsistent with the consensus that mitochondrial carriers exist as homo-dimers.
TL;DR: It is speculated that Mmm2p and Mmm1p are components of independent machinery, whose dynamic interactions are required to maintain mitochondrial shape and mtDNA structure.
Abstract: The mitochondrial outer membrane protein, Mmm1p, is required for normal mitochondrial shape in yeast. To identify new morphology proteins, we isolated mutations incompatible with the mmm1-1 mutant. One of these mutants, mmm2-1, is defective in a novel outer membrane protein. Lack of Mmm2p causes a defect in mitochondrial shape and loss of mitochondrial DNA (mtDNA) nucleoids. Like the Mmm1 protein (Aiken Hobbs, A.E., M. Srinivasan, J.M. McCaffery, and R.E. Jensen. 2001. J. Cell Biol. 152:401–410.), Mmm2p is located in dot-like particles on the mitochondrial surface, many of which are adjacent to mtDNA nucleoids. While some of the Mmm2p-containing spots colocalize with those containing Mmm1p, at least some of Mmm2p is separate from Mmm1p. Moreover, while Mmm2p and Mmm1p both appear to be part of large complexes, we find that Mmm2p and Mmm1p do not stably interact and appear to be members of two different structures. We speculate that Mmm2p and Mmm1p are components of independent machinery, whose dynamic interactions are required to maintain mitochondrial shape and mtDNA structure.
TL;DR: Unlike the yeast orthologue, SAMC catalysed virtually only countertransport, exhibited a higher transport affinity for SAM and was strongly inhibited by tannic acid and Bromocresol Purple.
Abstract: The mitochondrial carriers are a family of transport proteins that, with a few exceptions, are found in the inner membranes of mitochondria. They shuttle metabolites and cofactors through this membrane, and connect cytoplasmic functions with others in the matrix. SAM (S-adenosylmethionine) has to be transported into the mitochondria where it is converted into S-adenosylhomocysteine in methylation reactions of DNA, RNA and proteins. The transport of SAM has been investigated in rat liver mitochondria, but no protein has ever been associated with this activity. By using information derived from the phylogenetically distant yeast mitochondrial carrier for SAM and from related human expressed sequence tags, a human cDNA sequence was completed. This sequence was overexpressed in bacteria, and its product was purified, reconstituted into phospholipid vesicles and identified from its transport properties as the human mitochondrial SAM carrier (SAMC). Unlike the yeast orthologue, SAMC catalysed virtually only countertransport, exhibited a higher transport affinity for SAM and was strongly inhibited by tannic acid and Bromocresol Purple. SAMC was found to be expressed in all human tissues examined and was localized to the mitochondria. The physiological role of SAMC is probably to exchange cytosolic SAM for mitochondrial S-adenosylhomocysteine. This is the first report describing the identification and characterization of the human SAMC and its gene.
TL;DR: Arabidopsis mitochondria contain a protein with high sequence identity to a plastid protein import receptor, which is more similar to translocase of the outer mitochondrial membrane components than to chloroplastic Toc components.
TL;DR: Together, the data suggest that caspase-2 possesses an unparalleled ability to engage the mitochondrial apoptotic pathway by permeabilizing the outer mitochondrial membrane and/or by breaching the association of cytochrome c with the inner mitochondrial membrane.
TL;DR: The results make SCaMC one of most complex subfamilies of mitochondrial carriers and suggest that the large number of isoforms and splice variants may confer different calcium sensitivity to the transport activity of these carriers.
TL;DR: Genetical analysis revealed that the Mmr1p–Myo2p pathway is independent of the Ypt11p– myo 2p pathway, suggesting that an essential system for mitochondrial distribution is composed of two independent Myo2P pathways.
Abstract: Class V myosins play a pivotal role in organelle distribution. In the budding yeast, Myo2p, a class V myosin, is essential for mitochondrial distribution. We identified MMR1 as a high-dose suppressor of the myo2 mitochondrial defect and that Mmr1p resides restrictively on the bud-localizing mitochondria and forms a complex with Myo2p tail. Mmr1p loss delayed mitochondrial transfer to buds and completely abolished mitochondrial distribution in the absence of Ypt11p, which promotes mitochondrial distribution by complex formation with Myo2p tail. The myo2-573 mutation, which causes a mitochondrial distribution defect and inactivates the Mmr1p function, reduced association between Myo2p and Mmr1p and depolarized Mmr1p localization on mitochondria. These strongly suggest that Mmr1p is a key mitochondrial component of the link between Myo2p and mitochondria for Myo2p-dependent mitochondrial distribution. Genetical analysis revealed that the Mmr1p–Myo2p pathway is independent of the Ypt11p–Myo2p pathway, suggesting that an essential system for mitochondrial distribution is composed of two independent Myo2p pathways.
TL;DR: Domain mapping of yeast Cox17 reveals that the carboxyl-terminal segment of the protein has a function within the intermembrane space that is independent of copper ion binding.
01 Jan 2004
TL;DR: This paper discusses the role of Tetrahydrofolate Synthesis and One-Carbon Metabolism in Plants, and the roles of Reactive Oxygen Species and Antioxidants in Plant Mitochondria.
Abstract: Mitochondrial Structure and Function in Plants- Mitochondrial Morphology, Dynamics and Inheritance- Protein Targeting and Import- Gene Expression in Higher Plant Mitochondria- Mitochondria-Nucleus Interactions: Evidence for Mitochondrial Retrograde Communication in Plant Cells- Plant Mitochondrial Genome Evolution and Gene Transfer to the Nucleus- Mitochondrial Mutations in Plants- Proteome Analyses for Characterization of Plant Mitochondria- Alternative Mitochondrial Electron Transport Proteins in Higher Plants- Regulation of Electron Transport in the Respiratory Chain of Plant Mitochondria- Plant Mitochondrial Carriers- The Uniqueness of Tetrahydrofolate Synthesis and One-Carbon Metabolism in Plants- Photorespiration: Photosynthesis in the Mitochondria- Roles for Reactive Oxygen Species and Antioxidants in Plant Mitochondria
TL;DR: The results fit a model in which regulated interactions between Tim44 and mtHsp70, controlled by polypeptide binding, are required for efficient translocation across the mitochondrial inner membrane in vivo.
Abstract: Preproteins synthesized on cytosolic ribosomes, but destined for the mitochondrial matrix, pass through the presequence translocase of the inner membrane. Translocation is driven by the import motor, having at its core the essential chaperone mtHsp70 (Ssc1 in yeast). MtHsp70 is tethered to the translocon channel at the matrix side of the inner membrane by the peripheral membrane protein Tim44. A key question in mitochondrial import is how the mtHsp70-Tim44 interaction is regulated. Here we report that Tim44 interacts with both the ATPase and peptide-binding domains of mtHsp70. Disruption of these interactions upon binding of polypeptide substrates requires concerted conformational changes involving both domains of mtHsp70. Our results fit a model in which regulated interactions between Tim44 and mtHsp70, controlled by polypeptide binding, are required for efficient translocation across the mitochondrial inner membrane in vivo.
TL;DR: It is shown that, following its synthesis on mitochondrial ribosomes, subunit 6 of the ATPase (Atp6p) can be cross-linked to Atp10p, a mitochondrial inner membrane component necessary for the biogenesis of the hydrophobic F0 sector of theATPase.
TL;DR: RNA interference was successful in dramatically decreasing the abundance of the mRNAs for Ccp1 and Ccp2 in the RNAi strains, but did not exhibit a mutant carbon concentrating phenotype as determined by the cells’ apparent affinity for dissolved inorganic carbon.
Abstract: The unicellular green alga Chlamydomonas reinhardtii acclimates to a low-CO2 environment by modifying the expression of a number of messages. Many of the genes that increase in abundance during acclimation to low−2 are under the control of the putative transcription factor Cia5. C. reinhardtii mutants null for cia5 do not express several of the known low−2 inducible genes and do not grow in a low−2 environment. Two of the genes under the control of Cia5, Ccp1 and Ccp2, encode polypeptides that are localized to the chloroplast envelope and have a high degree of similarity to members of the mitochondrial carrier family of proteins. Since their discovery, Ccp1/2 have been candidates for bicarbonate uptake proteins of the chloroplast envelope membrane. In this report, RNA interference was successful in dramatically decreasing the abundance of the mRNAs for Ccp1 and Ccp2. The abundance of the Ccp1 and Ccp2 proteins were also reduced in the RNAi strains. The RNAi strains grew slower than WT in a low−2 environment, but did not exhibit a mutant carbon concentrating phenotype as determined by the cells’ apparent affinity for dissolved inorganic carbon. Possible explanations of this RNAi phenotype are discussed.
TL;DR: Protein expression studies indicate that DDP1 and TIMM13 show non-uniform expression in mammals, and expression is prominent in the large neurons in the brain, which is in agreement with the expression pattern of aralar1, which might contribute to the pathologic process associated with MTS.
Abstract: The biogenesis of the mitochondrial inner membrane is dependent on two distinct 70 kDa protein complexes. TlMM8a partners with TIMM13 in the mitochondrial intermembrane space to form a 70 kDa complex and facilitates the import of the inner membrane substrate TIMM23. We have identified a new class of substrates, citrin and aralarl, which are Ca 2+ -binding aspartate/glutamate carriers (AGCs) of the mitochondrial inner membrane, using cross-linking and immunoprecipitation assays in isolated mitochondria. The AGCs function in the aspartate-malate NADH shuttle that moves reducing equivalents from the cytosol to the mitochondrial matrix. Mohr-Tranebjaerg syndrome (MTSIDFN-1, deafnessldystonia syndrome) results from a mutation in deafness/dystonia protein 1/translocase of mitochondrial inner membrane 8a (DDP1/TIMM8a) and loss of the 70 kDa complex. A lymphoblast cell line derived from an MTS patient had decreased NADH levels and defects in mitochondrial protein import. Protein expression studies indicate that DDP1 and TIMM13 show non-uniform expression in mammals, and expression is prominent in the large neurons in the brain, which is in agreement with the expression pattern of aralar1. Thus, insufficient NADH shuttling, linked with changes in Ca 2+ concentration, in sensitive cells of the central nervous system might contribute to the pathologic process associated with MTS.