A Moonlighting Human Protein Is Involved in Mitochondrial Import of tRNA
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In yeast Saccharomyces cerevisiae, ~3% of the lysine transfer RNA acceptor 1 (tRK1) pool is imported into mitochondria while the second isoacceptor, tRK2, fully remains in the cytosol. The mitochondrial function of tRK1 is suggested to boost mitochondrial translation under stress conditions. Strikingly, yeast tRK1 can also be imported into human mitochondria in vivo, and can thus be potentially used as a vector to address RNAs with therapeutic anti-replicative capacity into mitochondria of sick cells. Better understanding of the targeting mechanism in yeast and human is thus critical. Mitochondrial import of tRK1 in yeast proceeds first through a drastic conformational rearrangement of tRK1 induced by enolase 2, which carries this freight to the mitochondrial pre-lysyl-tRNA synthetase (preMSK). The latter may cross the mitochondrial membranes to reach the matrix where imported tRK1 could be used by the mitochondrial translation apparatus. This work focuses on the characterization of the complex that tRK1 forms with human enolases and their role on the interaction between tRK1 and human pre-lysyl-tRNA synthetase (preKARS2).Keywords:
Mitochondrial matrix
Cells of the yeast Saccharomyces cerevisiae are transformable by DNA under non‐artificial conditions
Transformants of bakers' yeast (Saccharomyces cerevisiae) can be generated when non-growing cells metabolize sugars (without additional nutrients) in the presence of plasmid DNA. These results suggest that there is a mechanism by which DNA can naturally be taken up by the yeast cell. Natural transformation does not take place in common complete or minimal yeast culture media such as YPD and YNB. The starvation conditions used in our experiments thus seem to be an important prerequisite for such transformation events. Copyright © 2000 John Wiley & Sons, Ltd.
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Fluorescent protein-based reporters used to measure intracellular H2O2 were developed to overcome the limitations of small permeable dyes. The two major families of genetically encoded redox reporters are the reduction-oxidation sensitive green fluorescent protein (roGFP)-based proteins fused to peroxiredoxins and HyPer and derivatives. We have used the most sensitive probes of each family, roGFP2-Tpx1.C169S and HyPer7, to monitor steady-state and fluctuating levels of peroxides in fission yeast. While both are able to monitor the nanomolar fluctuations of intracellular H2O2, the former is two-five times more sensitive than HyPer7, and roGFP2-Tpx1.C169S is partially oxidized in the cytosol of wild-type cells while HyPer7 is fully reduced. We have successfully expressed HyPer7 in the mitochondrial matrix, and it is ~40% oxidized, suggesting higher steady-state levels of peroxides, in the low micromolar range, than in the cytosol. Cytosolic HyPer7 can detect negligible H2O2 in the cytosol from mitochondrial origin unless the main H2O2 scavenger, the cytosolic peroxiredoxin Tpx1, is absent, while mitochondrial HyPer7 is oxidized to the same extent in wild-type and ∆tpx1 cells. We conclude that there is a bidirectional flux of H2O2 across the matrix and the cytosol, but Tpx1 rapidly and efficiently scavenges mitochondrial-generated peroxides and stops their steady-state cytosolic levels rising.
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Scavenger
Peroxiredoxin
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Redox signaling from mitochondria (mt) to the cytosol and plasma membrane (PM) has been scarcely reported, such as in the case of hypoxic cell adaptation or (2-oxo-) 2-keto-isocaproate (KIC) β-like-oxidation stimulating insulin secretion in pancreatic β-cells. Mutual redox state influence between mitochondrial major compartments, the matrix and the intracristal space, and the cytosol is therefore derived theoretically in this article to predict possible conditions, when mt-to-cytosol and mt-to-PM signals may occur, as well as conditions in which the cytosolic redox signaling is not overwhelmed by the mitochondrial antioxidant capacity. Possible peroxiredoxin 3 participation in mt-to-cytosol redox signaling is discussed, as well as another specific case, whereby mitochondrial superoxide release is diminished, whereas the matrix MnSOD is activated. As a result, the enhanced conversion to H2O2 allows H2O2 diffusion into the cytosol, where it could be a predominant component of the H2O2 release. In both of these ways, mt-to-cytosol and mt-to-PM signals may be realized. Finally, the use of redox-sensitive probes is discussed, which disturb redox equilibria, and hence add a surplus redox-buffering to the compartment, where they are localized. Specifically, when attempts to quantify net H2O2 fluxes are to be made, this should be taken into account.
Mitochondrial matrix
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The release of two mitochondrial proteins, cytochrome c and apoptosis‐inducing factor (AIF), into the soluble cytoplasm of cells undergoing apoptosis is well established. Using spectrophotometric determination of enzyme activity, the accumulation of adenylate kinase (AK) activity in the cytosolic fraction of apoptotic cells has also been observed recently. However, three isozymes, AK1, AK2 and AK3, have been characterized in mammalian cells and shown to be localized in the cytosol, mitochondrial intermembrane space and mitochondrial matrix, respectively, and it is unknown which one of these isozymes accumulates in the cytosol during apoptosis. We now demonstrate that in apoptotic cells only AK2 was translocated into the cytosol concomitantly with cytochrome c . The amount of AK1 in cytosol, as well as the amount of matrix‐associated AK3, remained unchanged during the apoptotic process. Thus, our data suggest that only intermembrane proteins are released from mitochondria during the early phase of the apoptotic process.
Mitochondrial intermembrane space
Intermembrane space
Mitochondrial matrix
Mitochondrial apoptosis-induced channel
Apoptosis-inducing factor
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Abstract Hundreds of mitochondrial precursor proteins are synthesized in the cytosol and imported into mitochondria in a post-translational reaction. The early processes associated with mitochondrial protein targeting remain poorly understood. Here we show that in baker’s yeast, the cytosol has the capacity to transiently store matrix-destined precursors in dedicated deposits which we named MitoStores. MitoStores are strongly enhanced when protein import into mitochondria is competitively inhibited by a clogging of mitochondrial import sites, but also formed under physiological conditions when cells grow on non-fermentable carbon sources. MitoStores are enriched for a specific subset of nuclear encoded mitochondrial proteins, in particular those containing N-terminal mitochondrial targeting sequences. MitoStore formation is controlled by the heat shock proteins Hsp42 and Hsp104, potentially to suppress the toxic potential of accumulating mitochondrial precursor proteins. Thus, the cytosolic protein quality control system plays an active role during early stages in mitochondrial protein targeting by the coordinated and localized sequestration of mitochondrial precursor proteins. Summary The yeast cytosol can deposit precursors of mitochondrial proteins in specific granules called MitoStores. MitoStores are controlled by the cytosolic chaperone system, in particular by Hsp42 and Hsp104. MitoStore formation suppresses the toxicity arising from non-imported mitochondrial precursor proteins.
Mitochondrial matrix
Chaperone (clinical)
DNAJA3
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This protocol outlines a method for extracting total lipids from Baker's yeast, Saccharomyces cerevisiae. It has been adapted from Roy et al., J. Lipid Res. 2018. doi: 10.1194/jlr.M088559.
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One of the key feature of prions is the ability to be stable in two alternative conformations. Besides the intensively studied mammalian prions, there are also prion proteins present in the yeast Saccharomyces cerevisiae. Research in this field has lead to opposite hypotheses that explain the sense of presence of [PSI+] prion in yeast cells. Some authors postulate e of role of the prions in the evolution of S. cerevisiae, whereas other investigators point out the negative influence of these particles upon the yeast physiology. In recent years, yeast prions are used for anti-prion drug screening, because of common features with mammalian prions. This work presents the most intensively studied fields of the research carried out on [PSI+] prion in yeast.
Prion Proteins
Fungal prion
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Ethyl methanesulfonate
Methyl methanesulfonate
Strain (injury)
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Polyphosphate
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