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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 -
Annual Review of Plant Biology May 2023Chloroplasts are the defining plant organelles with responsibility for photosynthesis and other vital functions. To deliver these functions, they possess a complex... (Review)
Review
Chloroplasts are the defining plant organelles with responsibility for photosynthesis and other vital functions. To deliver these functions, they possess a complex proteome comprising thousands of largely nucleus-encoded proteins. Composition of the proteome is controlled by diverse processes affecting protein translocation and degradation-our focus here. Most chloroplast proteins are imported from the cytosol via multiprotein translocons in the outer and inner envelope membranes (the TOC and TIC complexes, respectively), or via one of several noncanonical pathways, and then sorted by different systems to organellar subcompartments. Chloroplast proteolysis is equally complex, involving the concerted action of internal proteases of prokaryotic origin and the nucleocytosolic ubiquitin-proteasome system (UPS). The UPS degrades unimported proteins in the cytosol and chloroplast-resident proteins via chloroplast-associated protein degradation (CHLORAD). The latter targets the TOC apparatus to regulate protein import, as well as numerous internal proteins directly, to reconfigure chloroplast functions in response to developmental and environmental signals.
Topics: Proteolysis; Proteome; Proteostasis; Chloroplasts; Ubiquitination; Chloroplast Proteins; Proteasome Endopeptidase Complex; Ubiquitin; Protein Transport; Plant Proteins
PubMed: 36854475
DOI: 10.1146/annurev-arplant-070122-032532 -
Biochimica Et Biophysica Acta.... Feb 2024Mitochondria import 1000-1300 different precursor proteins from the cytosol. The main mitochondrial entry gate is formed by the translocase of the outer membrane (TOM... (Review)
Review
Mitochondria import 1000-1300 different precursor proteins from the cytosol. The main mitochondrial entry gate is formed by the translocase of the outer membrane (TOM complex). Molecular coupling and modification of TOM subunits control and modulate protein import in response to cellular signaling. The TOM complex functions as regulatory hub to integrate mitochondrial protein biogenesis and quality control into the cellular proteostasis network.
Topics: Mitochondrial Precursor Protein Import Complex Proteins; Mitochondrial Proteins; Saccharomyces cerevisiae; Mitochondria; Mitochondrial Membranes
PubMed: 37951505
DOI: 10.1016/j.bbamcr.2023.119529 -
International Journal of Molecular... May 2022Mitochondria import about 1000 precursor proteins from the cytosol. The translocase of the outer membrane (TOM complex) forms the major entry site for precursor... (Review)
Review
Mitochondria import about 1000 precursor proteins from the cytosol. The translocase of the outer membrane (TOM complex) forms the major entry site for precursor proteins. Subsequently, membrane-bound protein translocases sort the precursor proteins into the outer and inner membrane, the intermembrane space, and the matrix. The phospholipid composition of mitochondrial membranes is critical for protein import. Structural and biochemical data revealed that phospholipids affect the stability and activity of mitochondrial protein translocases. Integration of proteins into the target membrane involves rearrangement of phospholipids and distortion of the lipid bilayer. Phospholipids are present in the interface between subunits of protein translocases and affect the dynamic coupling of partner proteins. Phospholipids are required for full activity of the respiratory chain to generate membrane potential, which in turn drives protein import across and into the inner membrane. Finally, outer membrane protein translocases are closely linked to organellar contact sites that mediate lipid trafficking. Altogether, intensive crosstalk between mitochondrial protein import and lipid biogenesis controls mitochondrial biogenesis.
Topics: Carrier Proteins; Mitochondria; Mitochondrial Membrane Transport Proteins; Mitochondrial Membranes; Mitochondrial Proteins; Phospholipids; Protein Transport; Saccharomyces cerevisiae Proteins
PubMed: 35563660
DOI: 10.3390/ijms23095274 -
Biomolecules Jul 2020Metabolite carriers of the mitochondrial inner membrane are crucial for cellular physiology since mitochondria contribute essential metabolic reactions and synthesize... (Review)
Review
Metabolite carriers of the mitochondrial inner membrane are crucial for cellular physiology since mitochondria contribute essential metabolic reactions and synthesize the majority of the cellular ATP. Like almost all mitochondrial proteins, carriers have to be imported into mitochondria from the cytosol. Carrier precursors utilize a specialized translocation pathway dedicated to the biogenesis of carriers and related proteins, the carrier translocase of the inner membrane (TIM22) pathway. After recognition and import through the mitochondrial outer membrane via the translocase of the outer membrane (TOM) complex, carrier precursors are ushered through the intermembrane space by hexameric TIM chaperones and ultimately integrated into the inner membrane by the TIM22 carrier translocase. Recent advances have shed light on the mechanisms of TOM translocase and TIM chaperone function, uncovered an unexpected versatility of the machineries, and revealed novel components and functional crosstalk of the human TIM22 translocase.
Topics: Biological Transport; Carrier Proteins; Humans; Membrane Transport Proteins; Mitochondria; Mitochondrial Membranes; Mitochondrial Precursor Protein Import Complex Proteins; Mitochondrial Proteins; Signal Transduction
PubMed: 32645990
DOI: 10.3390/biom10071008 -
Genes May 2020Mitochondria serve as a hub for many cellular processes, including bioenergetics, metabolism, cellular signaling, redox balance, calcium homeostasis, and cell death. The... (Review)
Review
Mitochondria serve as a hub for many cellular processes, including bioenergetics, metabolism, cellular signaling, redox balance, calcium homeostasis, and cell death. The mitochondrial proteome includes over a thousand proteins, encoded by both the mitochondrial and nuclear genomes. The majority (~99%) of proteins are nuclear encoded that are synthesized in the cytosol and subsequently imported into the mitochondria. Within the mitochondria, polypeptides fold and assemble into their native functional form. Mitochondria health and integrity depend on correct protein import, folding, and regulated turnover termed as mitochondrial protein quality control (MPQC). Failure to maintain these processes can cause mitochondrial dysfunction that leads to various pathophysiological outcomes and the commencement of diseases. Here, we summarize the current knowledge about the role of different MPQC regulatory systems such as mitochondrial chaperones, proteases, the ubiquitin-proteasome system, mitochondrial unfolded protein response, mitophagy, and mitochondria-derived vesicles in the maintenance of mitochondrial proteome and health. The proper understanding of mitochondrial protein quality control mechanisms will provide relevant insights to treat multiple human diseases.
Topics: Cell Nucleus; Humans; Mitochondria; Mitochondrial Proteins; Mitophagy; Proteasome Endopeptidase Complex; Protein Biosynthesis; Protein Folding; Ubiquitin; Unfolded Protein Response
PubMed: 32443488
DOI: 10.3390/genes11050563 -
ELife Oct 2022A newly discovered pathway suggests histone proteins H3 and H4 are imported into the nucleus as individual units rather than joined together as heterodimers as was...
A newly discovered pathway suggests histone proteins H3 and H4 are imported into the nucleus as individual units rather than joined together as heterodimers as was previously thought.
Topics: Active Transport, Cell Nucleus; Cell Nucleus; Histones
PubMed: 36227650
DOI: 10.7554/eLife.83308 -
Cell Death & Disease Nov 2023Though TDP-43 protein can be translocated into mitochondria and causes mitochondrial damage in TDP-43 proteinopathy, little is known about how TDP-43 is imported into...
Though TDP-43 protein can be translocated into mitochondria and causes mitochondrial damage in TDP-43 proteinopathy, little is known about how TDP-43 is imported into mitochondria. In addition, whether mitochondrial damage is caused by mitochondrial mislocalization of TDP-43 or a side effect of mitochondria-mediated TDP-43 degradation remains to be investigated. Here, our bioinformatical analyses reveal that mitophagy receptor gene FUNDC1 is co-expressed with TDP-43, and both TDP-43 and FUNDC1 expression is correlated with genes associated with mitochondrial protein import pathway in brain samples of patients diagnosed with TDP-43 proteinopathy. FUNDC1 promotes mitochondrial translocation of TDP-43 possibly by promoting TDP-43-TOM70 and DNAJA2-TOM70 interactions, which is independent of the LC3 interacting region of FUNDC1 in cellular experiments. In the transgenic fly model of TDP-43 proteinopathy, overexpressing FUNDC1 enhances TDP-43 induced mitochondrial damage, whereas down-regulating FUNDC1 reverses TDP-43 induced mitochondrial damage. FUNDC1 regulates mitochondria-mediated TDP-43 degradation not only by regulating mitochondrial TDP-43 import, but also by increasing LONP1 level and by activating mitophagy, which plays important roles in cytosolic TDP-43 clearance. Together, this study not only uncovers the mechanism of mitochondrial TDP-43 import, but also unravels the active role played by mitochondria in regulating TDP-43 homeostasis.
Topics: Humans; ATP-Dependent Proteases; DNA-Binding Proteins; HSP40 Heat-Shock Proteins; Membrane Proteins; Mitochondria; Mitochondrial Proteins; Mitophagy; TDP-43 Proteinopathies
PubMed: 37951930
DOI: 10.1038/s41419-023-06261-6 -
Trends in Cell Biology May 2024Peroxisomes are vital metabolic organelles that import their lumenal (matrix) enzymes from the cytosol using mobile receptors. Surprisingly, the receptors can even... (Review)
Review
Peroxisomes are vital metabolic organelles that import their lumenal (matrix) enzymes from the cytosol using mobile receptors. Surprisingly, the receptors can even import folded proteins, but the underlying mechanism has been a mystery. Recent results reveal how import receptors shuttle cargo into peroxisomes. The cargo-bound receptors move from the cytosol across the peroxisomal membrane completely into the matrix by a mechanism that resembles transport through the nuclear pore. The receptors then return to the cytosol through a separate retrotranslocation channel, leaving the cargo inside the organelle. This cycle concentrates imported proteins within peroxisomes, and the energy for cargo import is supplied by receptor export. Peroxisomal protein import thus fundamentally differs from other previously known mechanisms for translocating proteins across membranes.
Topics: Peroxisomes; Protein Transport; Humans; Animals; Cytosol; Receptors, Cytoplasmic and Nuclear
PubMed: 37743160
DOI: 10.1016/j.tcb.2023.08.005