Machinery for protein sorting and assembly in the mitochondrial outer membrane

Wiedemann, Nils; Kozjak, Vera; Chacińska, Agnieszka; Schönfisch, Birgit; Rospert, Sabine; Ryan, Michael; Pfanner, Nikolaus; Meisinger, Chris

doi:10.1038/nature01753

Cited by 352 publications

(469 citation statements)

References 24 publications

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“…To do this, we developed a BN-PAGE based assay to analyze assembly of newly imported subunits of complex IV into preexisting protein complexes. Similar import and assembly assays have successfully been used to assess outer membrane protein complex biogenesis (Krimmer et al, 2001;Model et al, 2001;Kozjak et al, 2003;Paschen et al, 2003;Wiedemann et al, 2003). Newly imported Cox5a assembled into the complex Figure 6.…”

Section: Taz1 and Respiratory Chain Complexesmentioning

confidence: 98%

Taz1, an Outer Mitochondrial Membrane Protein, Affects Stability and Assembly of Inner Membrane Protein Complexes: Implications for Barth Syndrome

Brandner

Mick

Frazier

et al. 2005

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The Saccharomyces cerevisiae Taz1 protein is the orthologue of human Tafazzin, a protein that when inactive causes Barth Syndrome (BTHS), a severe inherited X-linked disease. Taz1 is a mitochondrial acyltransferase involved in the remodeling of cardiolipin. We show that Taz1 is an outer mitochondrial membrane protein exposed to the intermembrane space (IMS). Transport of Taz1 into mitochondria depends on the receptor Tom5 of the translocase of the outer membrane (TOM complex) and the small Tim proteins of the IMS, but is independent of the sorting and assembly complex (SAM). TAZ1 deletion in yeast leads to growth defects on nonfermentable carbon sources, indicative of a defect in respiration. Because cardiolipin has been proposed to stabilize supercomplexes of the respiratory chain complexes III and IV, we assess supercomplexes in taz1⌬ mitochondria and show that these are destabilized in taz1⌬ mitochondria. This leads to a selective release of a complex IV monomer from the III 2 IV 2 supercomplex. In addition, assembly analyses of newly imported subunits into complex IV show that incorporation of the complex IV monomer into supercomplexes is affected in taz1⌬ mitochondria. We conclude that inactivation of Taz1 affects both assembly and stability of respiratory chain complexes in the inner membrane of mitochondria. INTRODUCTIONBarth Syndrome is an X-linked recessive disorder that is characterized by cardioskeletal myopathy, neutropenia, increased urine levels of 3-methylglutaconic acid, abnormal mitochondria, and respiratory chain dysfunction (Barth et al., 1983(Barth et al., , 1996Kelley et al., 1991;D'Adamo et al., 1997). The disease is often fatal in infancy and early childhood because of cardiac failure and bacterial infections (Barth et al., 2004). Bione et al. (1996) identified the gene responsible, termed Tafazzin (TAZ), and localized it to region q28 on the X chromosome. Sequence analyses demonstrate that the Taz protein is highly conserved from yeast to man and that it displays sequence similarity to acyltransferases that participate in the metabolism of phospholipids (Neuwald, 1997). Phospholipid analyses of fibroblasts from patients and yeast taz1⌬ mutant cells show reduced cardiolipin levels and an altered acyl chain composition (Vreken et al., 2000;Vaz et al., 2003;Xu et al., 2003;Gu et al., 2004).Cardiolipin is formed by two glycerol-linked phosphatidyl moieties. The four acyl side chains are usually monoand di-unsaturated fatty acids in higher eukaryotes. Remodeling of cardiolipin through a cycle of deacylation and successive reacylation leads to the final and specific acyl composition. In heart and skeletal muscle mitochondria the tetralinoleoyl species predominates Xu et al., 2003;Hatch, 2004). Cardiolipin is primarily found in the mitochondrial membranes of eukaryotes (Hoch, 1992) and the bacterial cytoplasmic membrane. Although the molecular function of cardiolipin is still unclear, several studies have suggested that it is required for the proper function of some proteins and protein complexe...

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Section: Taz1 and Respiratory Chain Complexesmentioning

confidence: 98%

Taz1, an Outer Mitochondrial Membrane Protein, Affects Stability and Assembly of Inner Membrane Protein Complexes: Implications for Barth Syndrome

Brandner

Mick

Frazier

et al. 2005

MBoC

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190

150

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“…1). These two MOM complexes, the general import pore TOM and the SAM insertase, allow for the entire translocation and insertion of nearly all newly synthesized proteins destined to the mitochondrial organelle (2,3). The third protein family of typically high abundance (Ϸ10,000 copies per mitochondrion) is termed voltage-dependent anion channels (VDACs), because of the voltage sensitivity of its open probability (4,5).…”

mentioning

confidence: 99%

Structure of the human voltage-dependent anion channel

Bayrhuber

Meins

Habeck

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

508

626

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The voltage-dependent anion channel (VDAC), also known as mitochondrial porin, is the most abundant protein in the mitochondrial outer membrane (MOM). VDAC is the channel known to guide the metabolic flux across the MOM and plays a key role in mitochondrially induced apoptosis. Here, we present the 3D structure of human VDAC1, which was solved conjointly by NMR spectroscopy and x-ray crystallography. Human VDAC1 (hVDAC1) adopts a ␤-barrel architecture composed of 19 ␤-strands with an ␣-helix located horizontally midway within the pore. Bioinformatic analysis indicates that this channel architecture is common to all VDAC proteins and is adopted by the general import pore TOM40 of mammals, which is also located in the MOM.T he outer membrane of mitochondria (MOM) contains three integral membrane protein families, two of which form channels as part of larger protein complexes (for review, see ref. 1). These two MOM complexes, the general import pore TOM and the SAM insertase, allow for the entire translocation and insertion of nearly all newly synthesized proteins destined to the mitochondrial organelle (2, 3). The third protein family of typically high abundance (Ϸ10,000 copies per mitochondrion) is termed voltage-dependent anion channels (VDACs), because of the voltage sensitivity of its open probability (4, 5). Together, this small number of protein families is sufficient for full communication between mitochondria with their cellular environment (1).The VDAC channel was initially described as being reminiscent of bacterial porins and primarily responsible for the exchange of chemical energy equivalents between the cytosol and the mitochondrion (4, 6). Indeed, a variety of structural features (like barrel geometry and dimension) known from the bacterial precursors are maintained (7,8). By contrast, a variety of functions have been ascribed to the VDAC isoforms among which the direct coupling of the mitochondrial matrix to the energy maintenance of the cytosol seems to be the most general function (9). The structure of VDAC is of interest because of a substantial body of evidence connecting VDAC to apoptosis. It is suggested that VDAC is a critical player in the release of apoptogenic factors from mitochondria of mammalian cells, and consequently several hypotheses describing the mechanism of mitochondria-mediated apoptosis involving VDAC have been proposed (for review, see ref. 10). Results and DiscussionStructure Determination of hVDAC1: Combining NMR Spectroscopy and X-Ray Crystallography. In a parallel structural biology approach, we set out to characterize the structure of hVDAC1, the major isoform of this channel in mammalian tissues, by a combination of NMR spectroscopy and x-ray crystallography. The idea behind this project was to gain complementary structural information to have a solid basis for future studies, e.g., analysis of protein heterocomplex formation by NMR and crystal structures as a basis for drug target design. Only information derived from both methods and the application of an iterative s...

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“…They are then translocated across the outer membrane via the general-import pore of the TOM complex (5)(6)(7)(8). From the TOM complex, ␤-barrel precursors are relayed to a specialized hetero-oligomeric protein complex termed either topogenesis of outer-membrane ␤-barrel proteins (TOB complex) (9) or sorting and assembly machinery (SAM complex) (10).…”

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confidence: 99%

“…It is believed that the evolvement of 2 further TOB subunits, Mas37/Sam37/Tom37 and Tob38/Sam35/Tom38, is part of such an adaptation process. These latter 2 components are associated with Tob55 at the cytosolic side of the outer membrane (10,(15)(16)(17). The role of Mas37 in the biogenesis of mitochondrial ␤-barrel membrane proteins has not yet been identified.…”

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confidence: 99%

Signals in bacterial β-barrel proteins are functional in eukaryotic cells for targeting to and assembly in mitochondria

Walther

Papić

Bos

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

108

127

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The outer membranes of Gram-negative bacteria, mitochondria, and chloroplasts harbor ␤-barrel proteins. The signals that allow precursors of such proteins to be targeted to mitochondria were not characterized so far. To better understand the mechanism by which ␤-barrel precursor proteins are recognized and sorted within eukaryotic cells, we expressed the bacterial ␤-barrel proteins PhoE, OmpA, Omp85, and OmpC in Saccharomyces cerevisiae and demonstrated that they were imported into mitochondria. A detailed investigation of the import pathway of PhoE revealed that it is shared with mitochondrial ␤-barrel proteins. PhoE interacts initially with surface import receptors, and its further sorting depends on components of the TOB/SAM complex. The bacterial Omp85 and PhoE integrated into the mitochondrial outer membrane as nativelike oligomers. For the latter protein this assembly depended on the C-terminal Phe residue, which is important also for the correct assembly of PhoE into the bacterial outer membrane. Collectively, it appears that mitochondrial ␤-barrel proteins have not evolved eukaryotic-specific signals to ensure their import into mitochondria. Furthermore, the signal for assembly of ␤-barrel proteins into the bacterial outer membrane is functional in mitochondria.outer membrane ͉ PhoE ͉ protein import ͉ TOB complex ͉ TOM complex

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Machinery for protein sorting and assembly in the mitochondrial outer membrane

Cited by 352 publications

References 24 publications

Taz1, an Outer Mitochondrial Membrane Protein, Affects Stability and Assembly of Inner Membrane Protein Complexes: Implications for Barth Syndrome

Taz1, an Outer Mitochondrial Membrane Protein, Affects Stability and Assembly of Inner Membrane Protein Complexes: Implications for Barth Syndrome

Structure of the human voltage-dependent anion channel

Signals in bacterial β-barrel proteins are functional in eukaryotic cells for targeting to and assembly in mitochondria

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