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Nature Dec 2020Dozens of genes contribute to the wide variation in human pigmentation. Many of these genes encode proteins that localize to the melanosome-the organelle, related to the...
Dozens of genes contribute to the wide variation in human pigmentation. Many of these genes encode proteins that localize to the melanosome-the organelle, related to the lysosome, that synthesizes pigment-but have unclear functions. Here we describe MelanoIP, a method for rapidly isolating melanosomes and profiling their labile metabolite contents. We use this method to study MFSD12, a transmembrane protein of unknown molecular function that, when suppressed, causes darker pigmentation in mice and humans. We find that MFSD12 is required to maintain normal levels of cystine-the oxidized dimer of cysteine-in melanosomes, and to produce cysteinyldopas, the precursors of pheomelanin synthesis made in melanosomes via cysteine oxidation. Tracing and biochemical analyses show that MFSD12 is necessary for the import of cysteine into melanosomes and, in non-pigmented cells, lysosomes. Indeed, loss of MFSD12 reduced the accumulation of cystine in lysosomes of fibroblasts from patients with cystinosis, a lysosomal-storage disease caused by inactivation of the lysosomal cystine exporter cystinosin. Thus, MFSD12 is an essential component of the cysteine importer for melanosomes and lysosomes.
Topics: Biological Transport; Cell Fractionation; Cell Line; Cysteine; Cystine; Cystinosis; Fibroblasts; Humans; Lysosomes; Melanins; Melanosomes; Membrane Proteins; Oxidation-Reduction
PubMed: 33208952
DOI: 10.1038/s41586-020-2937-x -
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 -
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 -
International Journal of Molecular... May 2022Protein import into the endoplasmic reticulum (ER) is the first step in the biogenesis of approximately 10,000 different soluble and membrane proteins of human cells,...
Protein import into the endoplasmic reticulum (ER) is the first step in the biogenesis of approximately 10,000 different soluble and membrane proteins of human cells, which amounts to about 30% of the proteome [...].
Topics: Endoplasmic Reticulum; Humans; Membrane Proteins; Protein Transport
PubMed: 35628123
DOI: 10.3390/ijms23105315 -
Cell Metabolism Mar 2021The haploinsufficiency of C9orf72 is implicated in the most common forms of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), but the full spectrum...
The haploinsufficiency of C9orf72 is implicated in the most common forms of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), but the full spectrum of C9orf72 functions remains to be established. Here, we report that C9orf72 is a mitochondrial inner-membrane-associated protein regulating cellular energy homeostasis via its critical role in the control of oxidative phosphorylation (OXPHOS). The translocation of C9orf72 from the cytosol to the inter-membrane space is mediated by the redox-sensitive AIFM1/CHCHD4 pathway. In mitochondria, C9orf72 specifically stabilizes translocase of inner mitochondrial membrane domain containing 1 (TIMMDC1), a crucial factor for the assembly of OXPHOS complex I. C9orf72 directly recruits the prohibitin complex to inhibit the m-AAA protease-dependent degradation of TIMMDC1. The mitochondrial complex I function is impaired in C9orf72-linked ALS/FTD patient-derived neurons. These results reveal a previously unknown function of C9orf72 in mitochondria and suggest that defective energy metabolism may underlie the pathogenesis of relevant diseases.
Topics: ATP-Dependent Proteases; ATPases Associated with Diverse Cellular Activities; Animals; Apoptosis Inducing Factor; C9orf72 Protein; Cell Line; Cell Survival; Electron Transport Complex I; Energy Metabolism; Humans; Mice; Mice, Inbred C57BL; Mice, Knockout; Mitochondria; Mitochondrial Precursor Protein Import Complex Proteins; Neurodegenerative Diseases; Oxidative Phosphorylation; RNA Interference; RNA, Small Interfering
PubMed: 33545050
DOI: 10.1016/j.cmet.2021.01.005 -
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 -
Nature Communications May 2023SMARCA4 (BRG1) and SMARCA2 (BRM) are the two paralogous ATPases of the SWI/SNF chromatin remodeling complexes frequently inactivated in cancers. Cells deficient in...
SMARCA4 (BRG1) and SMARCA2 (BRM) are the two paralogous ATPases of the SWI/SNF chromatin remodeling complexes frequently inactivated in cancers. Cells deficient in either ATPase have been shown to depend on the remaining counterpart for survival. Contrary to this paralog synthetic lethality, concomitant loss of SMARCA4/2 occurs in a subset of cancers associated with very poor outcomes. Here, we uncover that SMARCA4/2-loss represses expression of the glucose transporter GLUT1, causing reduced glucose uptake and glycolysis accompanied with increased dependency on oxidative phosphorylation (OXPHOS); adapting to this, these SMARCA4/2-deficient cells rely on elevated SLC38A2, an amino acid transporter, to increase glutamine import for fueling OXPHOS. Consequently, SMARCA4/2-deficient cells and tumors are highly sensitive to inhibitors targeting OXPHOS or glutamine metabolism. Furthermore, supplementation of alanine, also imported by SLC38A2, restricts glutamine uptake through competition and selectively induces death in SMARCA4/2-deficient cancer cells. At a clinically relevant dose, alanine supplementation synergizes with OXPHOS inhibition or conventional chemotherapy eliciting marked antitumor activity in patient-derived xenografts. Our findings reveal multiple druggable vulnerabilities of SMARCA4/2-loss exploiting a GLUT1/SLC38A2-mediated metabolic shift. Particularly, unlike dietary deprivation approaches, alanine supplementation can be readily applied to current regimens for better treatment of these aggressive cancers.
Topics: Humans; Glucose Transporter Type 1; Glutamine; Adenosine Triphosphatases; Neoplasms; Dietary Supplements; DNA Helicases; Nuclear Proteins; Transcription Factors
PubMed: 37210563
DOI: 10.1038/s41467-023-38594-3 -
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