Cytoplasmic chaperones determine the targeting pathway of precursor proteins to mitochondria.

Komiya, Tohru; Sakaguchi, Masao; Mihara, Katsuyoshi

doi:10.1002/j.1460-2075.1996.tb00370.x

Cited by 96 publications

(106 citation statements)

References 45 publications

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“…In vivo specificity might be achieved by the affinity of the various precursors for their respective receptors localized at the outer face of organelles. However, specificity might occur at an earlier step, since precursors may bind to cytosolic or membrane chaperones after, or even during, their translation (28,30,31). In the framework of this hypothesis, our data suggest that in vivo binding to chaperones and/or to chloroplast receptors requires, in addition to the transit peptide, residues of the mature TPT protein.…”

Section: Fig 2 Import Of Tpt5-cat and Tpt23-cat Into Isolated Chlormentioning

confidence: 66%

“…A more likely hypothesis would be that structural features required for in vivo mitochondrial or chloroplast uptake are missing in the TPT transit peptide. Failure of import could occur due to lack of interaction of the precursor either with specific chaperones involved in organellar targeting (28) or with receptors at the organelle outer membrane. The precursor would then be processed by a cytosolic protease.…”

Section: Fig 2 Import Of Tpt5-cat and Tpt23-cat Into Isolated Chlormentioning

confidence: 99%

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Different in Vitro and in Vivo Targeting Properties of the Transit Peptide of a Chloroplast Envelope Inner Membrane Protein

Silva-Filho¹,

Wieers²,

Flügge³

et al. 1997

Journal of Biological Chemistry

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The triose phosphate 3-phosphoglycerate phosphate translocator (TPT) is a chloroplast envelope inner membrane protein whose transit peptide has structural properties typical of a mitochondrial presequence. To study the TPT transit peptide in more detail, we constructed two chimeric genes encompassing the TPT transit peptide and either 5 or 23 amino-terminal residues of the mature TPT, both linked to the reporter chloramphenicol acetyltransferase (cat) gene. The precursors were synthesized in vitro and translocated to and processed in purified plant mitochondria. However, this import was not specific since both precursors were also imported into isolated chloroplasts. To extend this analysis in vivo, the chimeric genes were introduced into tobacco by genetic transformation. Analysis of CAT distribution in subcellular fractions of transgenic plants did not confirm the data obtained in vitro. With the construct retaining only 5 residues of the mature TPT, CAT was found in the cytosolic fraction. Extension of the TPT transit peptide to 23 residues of the mature TPT allowed specific import and processing of CAT into chloroplasts. These results indicate that, despite its unusual structure, the TPT transit peptide is able to target a passenger protein specifically into chloroplasts, provided that NH 2 -terminal residues of the mature TPT are still present. The discrepancy between the in vitro and in vivo data suggests that the translocation machinery is more stringent in the latter case and that sorting of proteins might not be addressed adequately by in vitro experiments.

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Section: Fig 2 Import Of Tpt5-cat and Tpt23-cat Into Isolated Chlormentioning

confidence: 66%

Section: Fig 2 Import Of Tpt5-cat and Tpt23-cat Into Isolated Chlormentioning

confidence: 99%

Different in Vitro and in Vivo Targeting Properties of the Transit Peptide of a Chloroplast Envelope Inner Membrane Protein

Silva-Filho¹,

Wieers²,

Flügge³

et al. 1997

Journal of Biological Chemistry

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“…Although pADH and F 1 ␤ were reported to require external ATP (18), we found here that they do not require external ATP for their import into mitochondria and that the previously observed requirement of external ATP arose from the decrease in their import competency before binding to mitochondria. This means that, because MSF requires ATP to release the substrate precursor protein at the docking site of the TOM complex, Tom70 (24,25), the presequence-containing precursor proteins studied here do not require MSF in the reticulocyte lysate for their import into mitochondria either. Previous in vitro studies showed that MSF was required for mitochondrial protein import if artificially denatured precursor proteins were pre-loaded onto MSF before incubation with isolated mitochondria (24,25).…”

Section: Discussionmentioning

confidence: 97%

“…It has been shown that ctHsp70 is important for the maintenance of import competence of some mitochondrial precursor proteins (18,21,23). However other studies reported that mitochondrial precursor proteins bound to ctHsp70 can be transferred to Tom20 of the TOM complex without hydrolysis of ATP (24,25). MSF in the rat cytosol binds to mitochondrial precursor proteins, prevents their aggregate formation, and targets them to Tom70 of the TOM complex (26).…”

mentioning

confidence: 99%

“…MSF in the rat cytosol binds to mitochondrial precursor proteins, prevents their aggregate formation, and targets them to Tom70 of the TOM complex (26). In vitro import experiments with purified MSF showed that docking of the mitochondrial protein-MSF complex to Tom70 does not need ATP hydrolysis, but subsequent release of MSF from the TOM complex/precursor protein requires it (24,25). Based on the analyses of the requirement of external ATP for the import of various mitochondrial precursor proteins (18), Lithgow et al proposed that a group of precursor proteins that require external ATP for their import depend on MSF and enter mitochondria via Tom70 (27).…”

mentioning

confidence: 99%

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Reinvestigation of the Requirement of Cytosolic ATP for Mitochondrial Protein Import

Asai

Takahashi

Esaki

et al. 2004

Journal of Biological Chemistry

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Protein import into mitochondria requires the energy of ATP hydrolysis inside and/or outside mitochondria. Although the role of ATP in the mitochondrial matrix in mitochondrial protein import has been extensively studied, the role of ATP outside mitochondria (external ATP) remains only poorly characterized. Here we developed a protocol for depletion of external ATP without significantly reducing the import competence of precursor proteins synthesized in vitro with reticulocyte lysate. We tested the effects of external ATP on the import of various precursor proteins into isolated yeast mitochondria. We found that external ATP is required for maintenance of the import competence of mitochondrial precursor proteins but that, once they bind to mitochondria, the subsequent translocation of presequencecontaining proteins, but not the ADP/ATP carrier, proceeds independently of external ATP. Because depletion of cytosolic Hsp70 led to a decrease in the import competence of mitochondrial precursor proteins, external ATP is likely utilized by cytosolic Hsp70. In contrast, the ADP/ATP carrier requires external ATP for efficient import into mitochondria even after binding to mitochondria, a situation that is only partly attributed to cytosolic Hsp70.Many eukaryotic proteins have to move across one or more biological membrane(s) to reach their destinations after synthesis (1). Protein translocation across the organellar membranes is mediated by translocators or translocases, which are membrane-protein complexes and provide a protein-conducting channel through which organellar proteins thread, in most cases, in unfolded conformations. Several translocation systems can actively unfold precursor proteins and achieve their vectorial movement across the membranes by using various forms of energy (2, 3).Mitochondria consist of the outer and inner membranes and two aqueous compartments, the intermembrane space and matrix. The vast majority of mitochondrial proteins are synthesized in the cytosol and imported into mitochondria. Precursors of most matrix proteins and many inner membrane proteins have a positively charged presequence that contains targeting information for mitochondria and is removed by the processing peptidase in the matrix. These proteins utilize the translocase of the outer mitochondrial membrane (TOM) 1 to cross the outer membrane and the translocase of the inner mitochondrial membrane, the TIM23 complex, for translocation across the inner membrane (4, 5). The targeting information in the presequence is recognized by Tom20, a general presequence receptor subunit of the TOM complex (6). Polytopic inner membrane proteins, including members of the carrier protein family such as the ADP/ATP carrier (AAC), are not synthesized with cleavable presequences but instead contain internal mitochondrial targeting signals. Members of the carrier protein family utilize the TOM complex to cross the outer membrane and another translocase of the inner membrane, the TIM22 complex, for integration into the inner membrane (7,8). These...

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Targeting and insertion of nuclear-encoded preproteins into the mitochondrial outer membrane

Mihara

2000

Bioessays

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Most mitochondrial proteins are synthesized in the cytosol as preproteins with a cleavable presequence and are delivered to the import receptors on the mitochondria by cytoplasmic import factors. The proteins are then imported to the intramitochondrial compartments by the import systems of the outer and inner membranes, TOM and TIM. Mitochondrial outer membrane proteins are synthesized without a cleavable presequence and most of them contain hydrophobic transmembrane domains, which, in conjunction with the flanking segments, function as the mitochondria import signals. Some of the proteins are inserted into the outer membrane by the TOM machinery; the import signal probably arrests further translocation and is released from the translocation channel to the lipid bilayer. The other proteins are inserted into the membrane by a novel pathway independent of the TOM machinery. This article reviews recent developments in the biogenesis of mitochondrial outer membrane proteins. BioEssays 22:364–371, 2000. © 2000 John Wiley & Sons, Inc.

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Cytoplasmic chaperones determine the targeting pathway of precursor proteins to mitochondria.

Cited by 96 publications

References 45 publications

Different in Vitro and in Vivo Targeting Properties of the Transit Peptide of a Chloroplast Envelope Inner Membrane Protein

Different in Vitro and in Vivo Targeting Properties of the Transit Peptide of a Chloroplast Envelope Inner Membrane Protein

Reinvestigation of the Requirement of Cytosolic ATP for Mitochondrial Protein Import

Targeting and insertion of nuclear-encoded preproteins into the mitochondrial outer membrane

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