scholarly journals Two distinct membrane potential–dependent steps drive mitochondrial matrix protein translocation

2016 ◽  
Vol 216 (1) ◽  
pp. 83-92 ◽  
Author(s):  
Alexander Benjamin Schendzielorz ◽  
Christian Schulz ◽  
Oleksandr Lytovchenko ◽  
Anne Clancy ◽  
Bernard Guiard ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Mitochondrial Membrane ◽  
Matrix Protein ◽  
Protein Translocation ◽  
Driving Forces ◽  
Matrix Proteins ◽  
Mitochondrial Matrix ◽  
Inner Mitochondrial Membrane ◽  
The Matrix ◽  
Energy Dependent

Two driving forces energize precursor translocation across the inner mitochondrial membrane. Although the membrane potential (Δψ) is considered to drive translocation of positively charged presequences through the TIM23 complex (presequence translocase), the activity of the Hsp70-powered import motor is crucial for the translocation of the mature protein portion into the matrix. In this study, we show that mitochondrial matrix proteins display surprisingly different dependencies on the Δψ. However, a precursor’s hypersensitivity to a reduction of the Δψ is not linked to the respective presequence, but rather to the mature portion of the polypeptide chain. The presequence translocase constituent Pam17 is specifically recruited by the receptor Tim50 to promote the transport of hypersensitive precursors into the matrix. Our analyses show that two distinct Δψ-driven translocation steps energize precursor passage across the inner mitochondrial membrane. The Δψ- and Pam17-dependent import step identified in this study is positioned between the two known energy-dependent steps: Δψ-driven presequence translocation and adenosine triphosphate–driven import motor activity.

scholarly journals The Peroxisome Biogenesis Factors Pex4p, Pex22p, Pex1p, and Pex6p Act in the Terminal Steps of Peroxisomal Matrix Protein Import

2000 ◽  
Vol 20 (20) ◽  
pp. 7516-7526 ◽  
Author(s):  
Cynthia S. Collins ◽  
Jennifer E. Kalish ◽  
James C. Morrell ◽  
J. Michael McCaffery ◽  
Stephen J. Gould
Keyword(s):  
Matrix Protein ◽  
Protein Import ◽  
Protein Translocation ◽  
Matrix Proteins ◽  
Peroxisome Biogenesis ◽  
Peroxisomal Membrane ◽  
The Matrix ◽  
Peroxisomal Targeting ◽  
Targeting Signal ◽  
Mutant Cells

ABSTRACT Peroxisomes are independent organelles found in virtually all eukaryotic cells. Genetic studies have identified more than 20PEX genes that are required for peroxisome biogenesis. The role of most PEX gene products, peroxins, remains to be determined, but a variety of studies have established that Pex5p binds the type 1 peroxisomal targeting signal and is the import receptor for most newly synthesized peroxisomal matrix proteins. The steady-state abundance of Pex5p is unaffected in mostpex mutants of the yeast Pichia pastorisbut is severely reduced in pex4 andpex22 mutants and moderately reduced in pex1and pex6 mutants. We used these subphenotypes to determine the epistatic relationships among several groups ofpex mutants. Our results demonstrate that Pex4p acts after the peroxisome membrane synthesis factor Pex3p, the Pex5p docking factors Pex13p and Pex14p, the matrix protein import factors Pex8p, Pex10p, and Pex12p, and two other peroxins, Pex2p and Pex17p. Pex22p and the interacting AAA ATPases Pex1p and Pex6p were also found to act after Pex10p. Furthermore, Pex1p and Pex6p were found to act upstream of Pex4p and Pex22p. These results suggest that Pex1p, Pex4p, Pex6p, and Pex22p act late in peroxisomal matrix protein import, after matrix protein translocation. This hypothesis is supported by the phenotypes of the corresponding mutant strains. As has been shown previously for P. pastoris pex1,pex6, and pex22 mutant cells, we show here thatpex4Δ mutant cells contain peroxisomal membrane protein-containing peroxisomes that import residual amounts of peroxisomal matrix proteins.

scholarly journals Cation selectivity of the presequence translocase channel Tim23 is crucial for efficient protein import

eLife ◽  
2017 ◽  
Vol 6 ◽  
Author(s):  
Niels Denkert ◽  
Alexander Benjamin Schendzielorz ◽  
Mariam Barbot ◽  
Lennart Versemann ◽  
Frank Richter ◽  
...  
Keyword(s):  
Amino Acids ◽  
Mitochondrial Membrane ◽  
Protein Import ◽  
Matrix Proteins ◽  
Mitochondrial Matrix ◽  
Amino Acid Residues ◽  
Inner Mitochondrial Membrane ◽  
Cation Selectivity ◽  
Pore Lining ◽  
Positively Charged

Virtually all mitochondrial matrix proteins and a considerable number of inner membrane proteins carry a positively charged, N-terminal presequence and are imported by the TIM23 complex (presequence translocase) located in the inner mitochondrial membrane. The voltage-regulated Tim23 channel constitutes the actual protein-import pore wide enough to allow the passage of polypeptides with a secondary structure. In this study, we identify amino acids important for the cation selectivity of Tim23. Structure based mutants show that selectivity is provided by highly conserved, pore-lining amino acids. Mutations of these amino acid residues lead to reduced selectivity properties, reduced protein import capacity and they render the Tim23 channel insensitive to substrates. We thus show that the cation selectivity of the Tim23 channel is a key feature for substrate recognition and efficient protein import.

scholarly journals Mitochondrial Lon protease is a gatekeeper for proteins newly imported into the matrix

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Yuichi Matsushima ◽  
Kazuya Takahashi ◽  
Song Yue ◽  
Yuki Fujiyoshi ◽  
Hideaki Yoshioka ◽  
...  
Keyword(s):  
Protease Activity ◽  
Matrix Protein ◽  
Protein Import ◽  
Atp Hydrolysis ◽  
Lon Protease ◽  
Mitochondrial Matrix ◽  
The Matrix ◽  
Specific Proteins ◽  
Aggregation Activity ◽  
Hydrolysis Activity

AbstractHuman ATP-dependent Lon protease (LONP1) forms homohexameric, ring-shaped complexes. Depletion of LONP1 causes aggregation of a broad range of proteins in the mitochondrial matrix and decreases the levels of their soluble forms. The ATP hydrolysis activity, but not protease activity, of LONP1 is critical for its chaperone-like anti-aggregation activity. LONP1 forms a complex with the import machinery and an incoming protein, and protein aggregation is linked with matrix protein import. LONP1 also contributes to the degradation of imported, aberrant, unprocessed proteins using its protease activity. Taken together, our results show that LONP1 functions as a gatekeeper for specific proteins imported into the mitochondrial matrix.

scholarly journals Shedding light on the mitochondrial matrix through a functional membrane transporter

2020 ◽  
Vol 11 (4) ◽  
pp. 1052-1065 ◽  
Author(s):  
Alberto Blázquez-Moraleja ◽  
Ines Sáenz-de-Santa María ◽  
María D. Chiara ◽  
Delia Álvarez-Fernández ◽  
Inmaculada García-Moreno ◽  
...  
Keyword(s):  
Membrane Potential ◽  
Mitochondrial Membrane ◽  
Living Cells ◽  
Membrane Transporter ◽  
Mitochondrial Matrix ◽  
Functional Membrane

A BODIPY derivative of carnitine enters mitochondria regardless of their membrane potential and in an enantioselective way through a specific mitochondrial membrane transporter in living cells.

scholarly journals In Vitro Import of a Nuclearly Encoded tRNA into the Mitochondrion of Trypanosoma brucei

1999 ◽  
Vol 19 (9) ◽  
pp. 6253-6259 ◽  
Author(s):  
Audra E. Yermovsky-Kammerer ◽  
Stephen L. Hajduk
Keyword(s):  
Membrane Potential ◽  
Trypanosoma Brucei ◽  
Mitochondrial Membrane ◽  
Protein Component ◽  
Proper Function ◽  
Mitochondrial Rna ◽  
Inner Mitochondrial Membrane ◽  
Trna Import ◽  
Trna Substrate

ABSTRACT All of the mitochondrial tRNAs of Trypanosoma bruceihave been shown to be encoded in the nucleus and must be imported into the mitochondrion. The import of nuclearly encoded tRNAs into the mitochondrion has been demonstrated in a variety of organisms and is essential for proper function in the mitochondrion. An in vitro import assay has been developed to study the pathway of tRNA import inT. brucei. The in vitro system utilizes crude isolated trypanosome mitochondria and synthetic RNAs transcribed from a cloned nucleus-encoded tRNA gene cluster. The substrate, composed of tRNASer and tRNALeu, is transcribed in tandem with a 59-nucleotide intergenic region. The tandem tRNA substrate is imported rapidly, while the mature-size tRNALeu fails to be imported in this system. These results suggest that the preferred substrate for tRNA import into trypanosome mitochondria is a precursor molecule composed of tandemly linked tRNAs. Import of the tandem tRNA substrate requires (i) a protein component that is associated with the surface of the mitochondrion, (ii) ATP pools both outside and within the mitochondrion, and (iii) a membrane potential. Dissipation of the proton gradient across the inner mitochondrial membrane by treatment with an uncoupling agent inhibits import of the tandem tRNA substrate. Characterization of the import requirements indicates that mitochondrial RNA import proceeds by a pathway including a protein component associated with the outer mitochondrial membrane, ATP-dependent steps, and a mitochondrial membrane potential.

scholarly journals CO2 and HCO3- Permeability of the Rat Liver Mitochondrial Membrane

2016 ◽  
Vol 39 (5) ◽  
pp. 2014-2024 ◽  
Author(s):  
Mariela Arias-Hidalgo ◽  
Jan Hegermann ◽  
Georgios Tsiavaliaris ◽  
Fabrizio Carta ◽  
Claudiu T. Supuran ◽  
...  
Keyword(s):  
Cell Membrane ◽  
Mitochondrial Membrane ◽  
Gas Permeability ◽  
Alternative Pathway ◽  
Biological Membrane ◽  
Red Cell ◽  
Inner Mitochondrial Membrane ◽  
Red Cell Membrane ◽  
The Matrix ◽  
Rat Livers

Background/Aims: Across the mitochondrial membrane an exceptionally intense exchange of O2 and CO2 occurs. We have asked, 1) whether the CO2 permeability, PM,CO2, of this membrane is also exceptionally high, and 2) whether the mitochondrial membrane is sufficiently permeable to HCO3- to make passage of this ion an alternative pathway for exit of metabolically produced CO2. Methods: The two permeabilities were measured using the previously published mass spectrometric 18O exchange technique to study suspensions of mitochondria freshly isolated from rat livers. The mitochondria were functionally and morphologically in excellent condition. Results: The intramitochondrial CA activity was exclusively localized in the matrix. PM,CO2 of the inner mitochondrial membrane was 0.33 (SD ± 0.03) cm/s, which is the highest value reported for any biological membrane, even two times higher than PM,CO2 of the red cell membrane. PM,HCO3- was 2· 10-6 (SD ± 2· 10-6) cm/s and thus extremely low, almost 3 orders of magnitude lower than PM,HCO3- of the red cell membrane. Conclusion: The inner mitochondrial membrane is almost impermeable to HCO3- but extremely permeable to CO2. Since gas channels are absent, this membrane constitutes a unique example of a membrane of very high gas permeability due to its extremely low content of cholesterol.

Mechanisms by which mitochondria transport calcium

1990 ◽  
Vol 258 (5) ◽  
pp. C755-C786 ◽  
Author(s):  
T. E. Gunter ◽  
D. R. Pfeiffer
Keyword(s):  
Membrane Potential ◽  
Mitochondrial Membrane ◽  
Permeability Transition ◽  
Electrochemical Gradient ◽  
Matrix Space ◽  
Available Energy ◽  
Outward Transport ◽  
Wide Range ◽  
The Matrix ◽  
Efflux Mechanism

It has been firmly established that the rapid uptake of Ca2+ by mitochondria from a wide range of sources is mediated by a uniporter which permits transport of the ion down its electrochemical gradient. Several mechanisms of Ca2+ efflux from mitochondria have also been extensively discussed in the literature. Energized mitochondria must expend a significant amount of energy to transport Ca2+ against its electrochemical gradient from the matrix space to the external space. Two separate mechanisms have been found to mediate this outward transport: a Ca2+/nNa+ exchanger and a Na(+)-independent efflux mechanism. These efflux mechanisms are considered from the perspective of available energy. In addition, a reversible Ca2(+)-induced increase in inner membrane permeability can also occur. The induction of this permeability transition is characterized by swelling of the mitochondria, leakiness to small ions such as K+, Mg2+, and Ca2+, and loss of the mitochondrial membrane potential. It has been suggested that the permeability transition and its reversal may also function as a mitochondrial Ca2+ efflux mechanism under some conditions. The characteristics of each of these mechanisms are discussed, as well as their possible physiological functions.

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