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Nature Dec 2020Mitochondria require nicotinamide adenine dinucleotide (NAD) to carry out the fundamental processes that fuel respiration and mediate cellular energy transduction....
Mitochondria require nicotinamide adenine dinucleotide (NAD) to carry out the fundamental processes that fuel respiration and mediate cellular energy transduction. Mitochondrial NAD transporters have been identified in yeast and plants, but their existence in mammals remains controversial. Here we demonstrate that mammalian mitochondria can take up intact NAD, and identify SLC25A51 (also known as MCART1)-an essential mitochondrial protein of previously unknown function-as a mammalian mitochondrial NAD transporter. Loss of SLC25A51 decreases mitochondrial-but not whole-cell-NAD content, impairs mitochondrial respiration, and blocks the uptake of NAD into isolated mitochondria. Conversely, overexpression of SLC25A51 or SLC25A52 (a nearly identical paralogue of SLC25A51) increases mitochondrial NAD levels and restores NAD uptake into yeast mitochondria lacking endogenous NAD transporters. Together, these findings identify SLC25A51 as a mammalian transporter capable of importing NAD into mitochondria.
Topics: Animals; Biological Transport; Cell Line; Cell Respiration; Genetic Complementation Test; Humans; Mice; Mitochondria; Mitochondrial Proteins; NAD; Nucleotide Transport Proteins; Organic Cation Transport Proteins; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins
PubMed: 32906142
DOI: 10.1038/s41586-020-2741-7 -
Annual Review of Biophysics May 2020Mitochondria are essential organelles in eukaryotes. Most mitochondrial proteins are encoded by the nuclear genome and translated in the cytosol. Nuclear-encoded... (Review)
Review
Mitochondria are essential organelles in eukaryotes. Most mitochondrial proteins are encoded by the nuclear genome and translated in the cytosol. Nuclear-encoded mitochondrial proteins need to be imported, processed, folded, and assembled into their functional states. To maintain protein homeostasis (proteostasis), mitochondria are equipped with a distinct set of quality control machineries. Deficiencies in such systems lead to mitochondrial dysfunction, which is a hallmark of aging and many human diseases, such as neurodegenerative diseases, cardiovascular diseases, and cancer. In this review, we discuss the unique challenges and solutions of proteostasis in mitochondria. The import machinery coordinates with mitochondrial proteases and chaperones to maintain the mitochondrial proteome. Moreover, mitochondrial proteostasis depends on cytosolic protein quality control mechanisms during crises. In turn, mitochondria facilitate cytosolic proteostasis. Increasing evidence suggests that enhancing mitochondrial proteostasis may hold therapeutic potential to protect against protein aggregation-associated cellular defects.
Topics: Cell Nucleus; Cytosol; Humans; Mitochondria; Mitochondrial Proteins; Proteostasis
PubMed: 31928428
DOI: 10.1146/annurev-biophys-121219-081604 -
Trends in Cell Biology Oct 2023Mitochondria perform crucial functions in cellular metabolism, protein and lipid biogenesis, quality control, and signaling. The systematic analysis of protein complexes... (Review)
Review
Mitochondria perform crucial functions in cellular metabolism, protein and lipid biogenesis, quality control, and signaling. The systematic analysis of protein complexes and interaction networks provided exciting insights into the structural and functional organization of mitochondria. Most mitochondrial proteins do not act as independent units, but are interconnected by stable or dynamic protein-protein interactions. Protein translocases are responsible for importing precursor proteins into mitochondria and form central elements of several protein interaction networks. These networks include molecular chaperones and quality control factors, metabolite channels and respiratory chain complexes, and membrane and organellar contact sites. Protein translocases link the distinct networks into an overarching network, the mitochondrial import network (MitimNet), to coordinate biogenesis, membrane organization and function of mitochondria.
PubMed: 37914576
DOI: 10.1016/j.tcb.2023.10.004 -
Biochimica Et Biophysica Acta.... Jan 2021Mitochondria accumulate copper in their matrix for the eventual maturation of the cuproenzymes cytochrome c oxidase and superoxide dismutase. Transport into the matrix... (Review)
Review
Mitochondria accumulate copper in their matrix for the eventual maturation of the cuproenzymes cytochrome c oxidase and superoxide dismutase. Transport into the matrix is achieved by mitochondrial carrier family (MCF) proteins. The major copper transporting MCF described to date in yeast is Pic2, which imports the metal ion into the matrix. Pic2 is one of ~30 MCFs that move numerous metabolites, nucleotides and co-factors across the inner membrane for use in the matrix. Genetic and biochemical experiments showed that Pic2 is required for cytochrome c oxidase activity under copper stress, and that it is capable of transporting ionic and complexed forms of copper. The Pic2 ortholog SLC25A3, one of 53 mammalian MCFs, functions as both a copper and a phosphate transporter. Depletion of SLC25A3 results in decreased accumulation of copper in the matrix, a cytochrome c oxidase defect and a modulation of cytosolic superoxide dismutase abundance. The regulatory roles for copper and cuproproteins resident to the mitochondrion continue to expand beyond the organelle. Mitochondrial copper chaperones have been linked to the modulation of cellular copper uptake and export and the facilitation of inter-organ communication. Recently, a role for matrix copper has also been proposed in a novel cell death pathway termed cuproptosis. This review will detail our understanding of the maturation of mitochondrial copper enzymes, the roles of mitochondrial signals in regulating cellular copper content, the proposed mechanisms of copper transport into the organelle and explore the evolutionary origins of copper homeostasis pathways.
Topics: Copper; Electron Transport Complex IV; Humans; Mitochondria; Mitochondrial Proteins; Molecular Chaperones; Phosphate Transport Proteins; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins; Superoxide Dismutase
PubMed: 32979421
DOI: 10.1016/j.bbamcr.2020.118867 -
The Journal of Biological Chemistry Jul 2022An ever-increasing number of proteins have been shown to translocate across various membranes of bacterial as well as eukaryotic cells in their folded states as a part... (Review)
Review
An ever-increasing number of proteins have been shown to translocate across various membranes of bacterial as well as eukaryotic cells in their folded states as a part of physiological and/or pathophysiological processes. Herein, we provide an overview of the systems/processes that are established or likely to involve the membrane translocation of folded proteins, such as protein export by the twin-arginine translocation system in bacteria and chloroplasts, unconventional protein secretion and protein import into the peroxisome in eukaryotes, and the cytosolic entry of proteins (e.g., bacterial toxins) and viruses into eukaryotes. We also discuss the various mechanistic models that have previously been proposed for the membrane translocation of folded proteins including pore/channel formation, local membrane disruption, membrane thinning, and transport by membrane vesicles. Finally, we introduce a newly discovered vesicular transport mechanism, vesicle budding and collapse, and present evidence that vesicle budding and collapse may represent a unifying mechanism that drives some (and potentially all) of folded protein translocation processes.
Topics: Bacteria; Bacterial Proteins; Eukaryota; Membrane Transport Proteins; Peroxisomes; Protein Folding; Protein Sorting Signals; Protein Transport; Twin-Arginine-Translocation System
PubMed: 35671825
DOI: 10.1016/j.jbc.2022.102107 -
International Journal of Molecular... Mar 2022Human mitochondrial disorders impact tissues with high energetic demands and can be associated with cardiac muscle disease (cardiomyopathy) and early mortality. However,... (Review)
Review
Human mitochondrial disorders impact tissues with high energetic demands and can be associated with cardiac muscle disease (cardiomyopathy) and early mortality. However, the mechanistic link between mitochondrial disease and the development of cardiomyopathy is frequently unclear. In addition, there is often marked phenotypic heterogeneity between patients, even between those with the same genetic variant, which is also not well understood. Several of the mitochondrial cardiomyopathies are related to defects in the maintenance of mitochondrial protein homeostasis, or proteostasis. This essential process involves the importing, sorting, folding and degradation of preproteins into fully functional mature structures inside mitochondria. Disrupted mitochondrial proteostasis interferes with mitochondrial energetics and ATP production, which can directly impact cardiac function. An inability to maintain proteostasis can result in mitochondrial dysfunction and subsequent mitophagy or even apoptosis. We review the known mitochondrial diseases that have been associated with cardiomyopathy and which arise from mutations in genes that are important for mitochondrial proteostasis. Genes discussed include DnaJ heat shock protein family member C19 (), mitochondrial import inner membrane translocase subunit TIM16 (), translocase of the inner mitochondrial membrane 50 (), mitochondrial intermediate peptidase (), X-prolyl-aminopeptidase 3 (), HtraA serine peptidase 2 (), caseinolytic mitochondrial peptidase chaperone subunit B () and heat shock 60-kD protein 1 (HSPD1). The identification and description of disorders with a shared mechanism of disease may provide further insights into the disease process and assist with the identification of potential therapeutics.
Topics: Cardiomyopathies; HSP40 Heat-Shock Proteins; Homeostasis; Humans; Mitochondria; Mitochondrial Membrane Transport Proteins; Mitochondrial Proteins; Peptide Hydrolases; Protein Transport; Proteostasis
PubMed: 35328774
DOI: 10.3390/ijms23063353 -
Biochemical Society Transactions Dec 2020The transport of histones from the cytoplasm to the nucleus of the cell, through the nuclear membrane, is a cellular process that regulates the supply of new histones in... (Review)
Review
The transport of histones from the cytoplasm to the nucleus of the cell, through the nuclear membrane, is a cellular process that regulates the supply of new histones in the nucleus and is key for DNA replication and transcription. Nuclear import of histones is mediated by proteins of the karyopherin family of nuclear transport receptors. Karyopherins recognize their cargos through linear motifs known as nuclear localization/export sequences or through folded domains in the cargos. Karyopherins interact with nucleoporins, proteins that form the nuclear pore complex, to promote the translocation of their cargos into the nucleus. When binding to histones, karyopherins not only function as nuclear import receptors but also as chaperones, protecting histones from non-specific interactions in the cytoplasm, in the nuclear pore and possibly in the nucleus. Studies have also suggested that karyopherins might participate in histones deposition into nucleosomes. In this review we describe structural and biochemical studies from the last two decades on how karyopherins recognize and transport the core histone proteins H3, H4, H2A and H2B and the linker histone H1 from the cytoplasm to the nucleus, which karyopherin is the major nuclear import receptor for each of these histones, the oligomeric state of histones during nuclear import and the roles of post-translational modifications, histone-chaperones and RanGTP in regulating these nuclear import pathways.
Topics: Active Transport, Cell Nucleus; Cell Cycle Proteins; Cell Nucleus; Cytoplasm; GTP Phosphohydrolases; Histones; Humans; Karyopherins; Molecular Chaperones; Nuclear Proteins; Protein Conformation; Protein Processing, Post-Translational; Receptors, Cytoplasmic and Nuclear; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins
PubMed: 33300986
DOI: 10.1042/BST20200572 -
Journal of Cell Science Aug 2023Peroxisomes are involved in a multitude of metabolic and catabolic pathways, as well as the innate immune system. Their dysfunction is linked to severe... (Review)
Review
Peroxisomes are involved in a multitude of metabolic and catabolic pathways, as well as the innate immune system. Their dysfunction is linked to severe peroxisome-specific diseases, as well as cancer and neurodegenerative diseases. To ensure the ability of peroxisomes to fulfill their many roles in the organism, more than 100 different proteins are post-translationally imported into the peroxisomal membrane and matrix, and their functionality must be closely monitored. In this Review, we briefly discuss the import of peroxisomal membrane proteins, and we emphasize an updated view of both classical and alternative peroxisomal matrix protein import pathways. We highlight different quality control pathways that ensure the degradation of dysfunctional peroxisomal proteins. Finally, we compare peroxisomal matrix protein import with other systems that transport folded proteins across membranes, in particular the twin-arginine translocation (Tat) system and the nuclear pore.
Topics: Membrane Proteins; Peroxisomes; Protein Transport; Intracellular Membranes
PubMed: 37552037
DOI: 10.1242/jcs.260999 -
Molecular Cell Aug 2022Iron is the most abundant transition metal essential for numerous cellular processes. Although most mammalian cells acquire iron through transferrin receptors, molecular...
Iron is the most abundant transition metal essential for numerous cellular processes. Although most mammalian cells acquire iron through transferrin receptors, molecular players of iron utilization under iron restriction are incompletely understood. To address this, we performed metabolism-focused CRISPRa gain-of-function screens, which revealed metabolic limitations under stress conditions. Iron restriction screens identified not only expected members of iron utilization pathways but also SLCO2B1, a poorly characterized membrane carrier. SLCO2B1 expression is sufficient to increase intracellular iron, bypass the essentiality of the transferrin receptor, and enable proliferation under iron restriction. Mechanistically, SLCO2B1 mediates heme analog import in cellular assays. Heme uptake by SLCO2B1 provides sufficient iron for proliferation through heme oxygenases. Notably, SLCO2B1 is predominantly expressed in microglia in the brain, and primary Slco2b1 mouse microglia exhibit strong defects in heme analog import. Altogether, our work identifies SLCO2B1 as a microglia-enriched plasma membrane heme importer and provides a genetic platform to identify metabolic limitations under stress conditions.
Topics: Animals; Biological Transport; Heme; Iron; Mammals; Membrane Transport Proteins; Mice; Organic Anion Transporters; Transcriptional Activation
PubMed: 35714613
DOI: 10.1016/j.molcel.2022.05.024 -
The FEBS Journal Nov 2022Most chloroplast proteins are nucleus-encoded, translated on cytoplasmic ribosomes as precursor proteins, and imported into chloroplasts through TOC and TIC, the... (Review)
Review
Most chloroplast proteins are nucleus-encoded, translated on cytoplasmic ribosomes as precursor proteins, and imported into chloroplasts through TOC and TIC, the translocons of the outer and inner chloroplast envelope membranes. While the composition of the TOC complex is well established, there is still some controversy about the importance of a recently identified TIC complex consisting of Tic20, Tic214, Tic100, and Tic56. TOC and TIC form a supercomplex with a protein channel at the junction of the outer and inner envelope membranes through which preproteins are pulled into the stroma by the ATP-powered Ycf2 complex consisting of several FtsH-like ATPases and/or by chloroplast Hsp proteins. Several components of the TOC/TIC system are moonlighting proteins with additional roles in chloroplast gene expression and metabolism. Chaperones and co-chaperones, associated with TOC and TIC on the cytoplasmic and stromal side of the chloroplast envelope, participate in the unfolding and folding of the precursor proteins and act together with the ubiquitin-proteasome system in protein quality control. Chloroplast protein import is also intimately linked with retrograde signaling, revealing altogether an unsuspected complexity in the regulation of this process.
Topics: Plant Proteins; Chloroplasts; Chloroplast Proteins; Protein Transport; Molecular Chaperones; Protein Precursors
PubMed: 35472255
DOI: 10.1111/febs.16464