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The MIA pathway: a key regulator of mitochondrial oxidative protein folding and biogenesis.

Mordas A, Tokatlidis K - Acc. Chem. Res. (2015)

Bottom Line: The solution NMR structure of Mia40 (and supporting biochemical experiments) showed that Mia40 is a novel type of disulfide donor whose recognition capacity for its substrates relies on a hydrophobic binding cleft found adjacent to a thiol active CPC motif.This consists of only 9 amino acids, found upstream or downstream of a unique Cys that is primed for docking to Mia40 when the substrate is accommodated in the Mia40 binding cleft.Maintenance of redox balance in mitochondria is crucial for normal cell physiology and depends on the cross-talk between the various redox signaling processes and the mitochondrial oxidative folding pathway.

View Article: PubMed Central - PubMed

Affiliation: †Institute of Molecular Cell and Systems Biology, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom.

ABSTRACT
Mitochondria are fundamental intracellular organelles with key roles in important cellular processes like energy production, Fe/S cluster biogenesis, and homeostasis of lipids and inorganic ions. Mitochondrial dysfunction is consequently linked to many human pathologies (cancer, diabetes, neurodegeneration, stroke) and apoptosis. Mitochondrial biogenesis relies on protein import as most mitochondrial proteins (about 10-15% of the human proteome) are imported after their synthesis in the cytosol. Over the last several years many mitochondrial translocation pathways have been discovered. Among them, the import pathway that targets proteins to the intermembrane space (IMS) stands out as it is the only one that couples import to folding and oxidation and results in the covalent modification of the incoming precursor that adopt internal disulfide bonds in the process (the MIA pathway). The discovery of this pathway represented a significant paradigm shift as it challenged the prevailing dogma that the endoplasmic reticulum is the only compartment of eukaryotic cells where oxidative folding can occur. The concept of the oxidative folding pathway was first proposed on the basis of folding and import data for the small Tim proteins that have conserved cysteine motifs and must adopt intramolecular disulfides after import so that they are retained in the organelle. The introduction of disulfides in the IMS is catalyzed by Mia40 that functions as a chaperone inducing their folding. The sulfhydryl oxidase Erv1 generates the disulfide pairs de novo using either molecular oxygen or, cytochrome c and other proteins as terminal electron acceptors that eventually link this folding process to respiration. The solution NMR structure of Mia40 (and supporting biochemical experiments) showed that Mia40 is a novel type of disulfide donor whose recognition capacity for its substrates relies on a hydrophobic binding cleft found adjacent to a thiol active CPC motif. Targeting of the substrates to this pathway is guided by a novel type of IMS targeting signal called ITS or MISS. This consists of only 9 amino acids, found upstream or downstream of a unique Cys that is primed for docking to Mia40 when the substrate is accommodated in the Mia40 binding cleft. Different routes exist to complete the folding of the substrates and their final maturation in the IMS. Identification of new Mia40 substrates (some even without the requirement of their cysteines) reveals an expanded chaperone-like activity of this protein in the IMS. New evidence on the targeting of redox active proteins like thioredoxin, glutaredoxin, and peroxiredoxin into the IMS suggests the presence of redox-dependent regulatory mechanisms of the protein folding and import process in mitochondria. Maintenance of redox balance in mitochondria is crucial for normal cell physiology and depends on the cross-talk between the various redox signaling processes and the mitochondrial oxidative folding pathway.

No MeSH data available.


Related in: MedlinePlus

Electron transfer acrossthe MIA pathway in the mitochondrial IMS.Precursors that have been synthesized on cytosolic ribosomes enterthe mitochondria through the TOM complex, in a reduced and unfoldedstate. Those destined for detainment in the IMS by oxidative foldingfollow the MIA pathway. Electron flow begins from the reduced precursorto the redox active cysteine-proline-cysteine (CPC) motif of Mia40/MIA40,to the N-terminus of one Erv1/ALR subunit, to the Erv1/ALR core FADdomain of the C-terminus of the other Erv1/ALR subunit, to cytochrome c (Cyt c), to cytochrome c oxidase, and last to oxygen (O2). Alternatively, electronscan flow from Erv1/ALR directly to O2, and in yeast fromCyt c to cytochrome c peroxidase(Ccp). Note that, in mammalian cells, MIA40 is soluble in the IMS.
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fig1: Electron transfer acrossthe MIA pathway in the mitochondrial IMS.Precursors that have been synthesized on cytosolic ribosomes enterthe mitochondria through the TOM complex, in a reduced and unfoldedstate. Those destined for detainment in the IMS by oxidative foldingfollow the MIA pathway. Electron flow begins from the reduced precursorto the redox active cysteine-proline-cysteine (CPC) motif of Mia40/MIA40,to the N-terminus of one Erv1/ALR subunit, to the Erv1/ALR core FADdomain of the C-terminus of the other Erv1/ALR subunit, to cytochrome c (Cyt c), to cytochrome c oxidase, and last to oxygen (O2). Alternatively, electronscan flow from Erv1/ALR directly to O2, and in yeast fromCyt c to cytochrome c peroxidase(Ccp). Note that, in mammalian cells, MIA40 is soluble in the IMS.

Mentions: In 2009, the full in vitro reconstitutedMIA pathway was reportedby the Koehler group using Tim13, as a twin CX3C substrate.20 Oxygen consumption assays were used to determinethe midpoint potentials (Em) of Mia40and Tim13 throughout the reaction, which began by incubating reducedTim13, Mia40, Erv1, and molecular oxygen. The resultant products wereoxidized Tim13 and hydrogen peroxide (H2O2),as expected. Importantly, the Em valueswere more positive along the reaction (from Tim13 to Mia40 to Erv1to oxygen), indicating that the electron transfer reaction was thermodynamicallyfavorable.20 Further support came froma study using Cox19 as a twin CX9C substrate and cytochrome c as the final electron acceptor21 showing a complete oxidation of Cox19. In this work, it was alsoreported that Erv1 functions as a noncovalently bound homodimer. Electronsfrom reduced Mia40 are shuttled to the N-terminus of one subunit ofErv1 and then onto the FAD domain of the C-terminus of the secondsubunit. These reconstitution assays in combination with detailedstructural studies of Mia40 and Erv1 began to reveal the molecularinteractions that result in electron transfer. A schematic depictionof the flow of electrons across the MIA pathway is shown in Figure 1.


The MIA pathway: a key regulator of mitochondrial oxidative protein folding and biogenesis.

Mordas A, Tokatlidis K - Acc. Chem. Res. (2015)

Electron transfer acrossthe MIA pathway in the mitochondrial IMS.Precursors that have been synthesized on cytosolic ribosomes enterthe mitochondria through the TOM complex, in a reduced and unfoldedstate. Those destined for detainment in the IMS by oxidative foldingfollow the MIA pathway. Electron flow begins from the reduced precursorto the redox active cysteine-proline-cysteine (CPC) motif of Mia40/MIA40,to the N-terminus of one Erv1/ALR subunit, to the Erv1/ALR core FADdomain of the C-terminus of the other Erv1/ALR subunit, to cytochrome c (Cyt c), to cytochrome c oxidase, and last to oxygen (O2). Alternatively, electronscan flow from Erv1/ALR directly to O2, and in yeast fromCyt c to cytochrome c peroxidase(Ccp). Note that, in mammalian cells, MIA40 is soluble in the IMS.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4551283&req=5

fig1: Electron transfer acrossthe MIA pathway in the mitochondrial IMS.Precursors that have been synthesized on cytosolic ribosomes enterthe mitochondria through the TOM complex, in a reduced and unfoldedstate. Those destined for detainment in the IMS by oxidative foldingfollow the MIA pathway. Electron flow begins from the reduced precursorto the redox active cysteine-proline-cysteine (CPC) motif of Mia40/MIA40,to the N-terminus of one Erv1/ALR subunit, to the Erv1/ALR core FADdomain of the C-terminus of the other Erv1/ALR subunit, to cytochrome c (Cyt c), to cytochrome c oxidase, and last to oxygen (O2). Alternatively, electronscan flow from Erv1/ALR directly to O2, and in yeast fromCyt c to cytochrome c peroxidase(Ccp). Note that, in mammalian cells, MIA40 is soluble in the IMS.
Mentions: In 2009, the full in vitro reconstitutedMIA pathway was reportedby the Koehler group using Tim13, as a twin CX3C substrate.20 Oxygen consumption assays were used to determinethe midpoint potentials (Em) of Mia40and Tim13 throughout the reaction, which began by incubating reducedTim13, Mia40, Erv1, and molecular oxygen. The resultant products wereoxidized Tim13 and hydrogen peroxide (H2O2),as expected. Importantly, the Em valueswere more positive along the reaction (from Tim13 to Mia40 to Erv1to oxygen), indicating that the electron transfer reaction was thermodynamicallyfavorable.20 Further support came froma study using Cox19 as a twin CX9C substrate and cytochrome c as the final electron acceptor21 showing a complete oxidation of Cox19. In this work, it was alsoreported that Erv1 functions as a noncovalently bound homodimer. Electronsfrom reduced Mia40 are shuttled to the N-terminus of one subunit ofErv1 and then onto the FAD domain of the C-terminus of the secondsubunit. These reconstitution assays in combination with detailedstructural studies of Mia40 and Erv1 began to reveal the molecularinteractions that result in electron transfer. A schematic depictionof the flow of electrons across the MIA pathway is shown in Figure 1.

Bottom Line: The solution NMR structure of Mia40 (and supporting biochemical experiments) showed that Mia40 is a novel type of disulfide donor whose recognition capacity for its substrates relies on a hydrophobic binding cleft found adjacent to a thiol active CPC motif.This consists of only 9 amino acids, found upstream or downstream of a unique Cys that is primed for docking to Mia40 when the substrate is accommodated in the Mia40 binding cleft.Maintenance of redox balance in mitochondria is crucial for normal cell physiology and depends on the cross-talk between the various redox signaling processes and the mitochondrial oxidative folding pathway.

View Article: PubMed Central - PubMed

Affiliation: †Institute of Molecular Cell and Systems Biology, College of Medical Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom.

ABSTRACT
Mitochondria are fundamental intracellular organelles with key roles in important cellular processes like energy production, Fe/S cluster biogenesis, and homeostasis of lipids and inorganic ions. Mitochondrial dysfunction is consequently linked to many human pathologies (cancer, diabetes, neurodegeneration, stroke) and apoptosis. Mitochondrial biogenesis relies on protein import as most mitochondrial proteins (about 10-15% of the human proteome) are imported after their synthesis in the cytosol. Over the last several years many mitochondrial translocation pathways have been discovered. Among them, the import pathway that targets proteins to the intermembrane space (IMS) stands out as it is the only one that couples import to folding and oxidation and results in the covalent modification of the incoming precursor that adopt internal disulfide bonds in the process (the MIA pathway). The discovery of this pathway represented a significant paradigm shift as it challenged the prevailing dogma that the endoplasmic reticulum is the only compartment of eukaryotic cells where oxidative folding can occur. The concept of the oxidative folding pathway was first proposed on the basis of folding and import data for the small Tim proteins that have conserved cysteine motifs and must adopt intramolecular disulfides after import so that they are retained in the organelle. The introduction of disulfides in the IMS is catalyzed by Mia40 that functions as a chaperone inducing their folding. The sulfhydryl oxidase Erv1 generates the disulfide pairs de novo using either molecular oxygen or, cytochrome c and other proteins as terminal electron acceptors that eventually link this folding process to respiration. The solution NMR structure of Mia40 (and supporting biochemical experiments) showed that Mia40 is a novel type of disulfide donor whose recognition capacity for its substrates relies on a hydrophobic binding cleft found adjacent to a thiol active CPC motif. Targeting of the substrates to this pathway is guided by a novel type of IMS targeting signal called ITS or MISS. This consists of only 9 amino acids, found upstream or downstream of a unique Cys that is primed for docking to Mia40 when the substrate is accommodated in the Mia40 binding cleft. Different routes exist to complete the folding of the substrates and their final maturation in the IMS. Identification of new Mia40 substrates (some even without the requirement of their cysteines) reveals an expanded chaperone-like activity of this protein in the IMS. New evidence on the targeting of redox active proteins like thioredoxin, glutaredoxin, and peroxiredoxin into the IMS suggests the presence of redox-dependent regulatory mechanisms of the protein folding and import process in mitochondria. Maintenance of redox balance in mitochondria is crucial for normal cell physiology and depends on the cross-talk between the various redox signaling processes and the mitochondrial oxidative folding pathway.

No MeSH data available.


Related in: MedlinePlus