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Annual Review of Biochemistry Jun 2022Mitochondria are central to energy production, metabolism and signaling, and apoptosis. To make new mitochondria from preexisting mitochondria, the cell needs to import... (Review)
Review
Mitochondria are central to energy production, metabolism and signaling, and apoptosis. To make new mitochondria from preexisting mitochondria, the cell needs to import mitochondrial proteins from the cytosol into the mitochondria with the aid of translocators in the mitochondrial membranes. The translocase of the outer membrane (TOM) complex, an outer membrane translocator, functions as an entry gate for most mitochondrial proteins. Although high-resolution structures of the receptor subunits of the TOM complex were deposited in the early 2000s, those of entire TOM complexes became available only in 2019. The structural details of these TOM complexes, consisting of the dimer of the β-barrel import channel Tom40 and four α-helical membrane proteins, revealed the presence of several distinct paths and exits for the translocation of over 1,000 different mitochondrial precursor proteins. High-resolution structures of TOM complexes now open up a new era of studies on the structures, functions, and dynamics of the mitochondrial import system.
Topics: Carrier Proteins; Mitochondria; Mitochondrial Membrane Transport Proteins; Mitochondrial Precursor Protein Import Complex Proteins; Mitochondrial Proteins; Protein Transport; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins
PubMed: 35287471
DOI: 10.1146/annurev-biochem-032620-104527 -
Methods in Cell Biology 2020Distinct protein complements impart each of the chloroplast's three membranes and three aqueous spaces with specific functions essential for plant growth and...
Distinct protein complements impart each of the chloroplast's three membranes and three aqueous spaces with specific functions essential for plant growth and development. Chloroplasts capture light energy, synthesize macromolecular building blocks and specialized metabolites, and communicate environmental signals to the nucleus. Establishing and maintaining these processes requires approximately 3000 proteins derived from nuclear genes, constituting approximately 95% of the chloroplast proteome. These proteins are imported into chloroplasts from the cytosol, sorted to the correct subcompartment, and assembled into functioning complexes. In vitro import assays can reconstitute these processes in isolated chloroplasts. We describe methods for monitoring in vitro protein import using Pisum sativum chloroplasts and for protease protection, fractionation, and native protein electrophoresis that are commonly combined with the import assay. These techniques facilitate investigation of the import and sorting processes, of where a protein resides, and of how that protein functions.
Topics: Alkalies; Biological Assay; Chemical Fractionation; Chloroplasts; Cytological Techniques; Escherichia coli; Pisum sativum; Plant Proteins; Protein Biosynthesis; Protein Transport; Thermolysin; Trypsin
PubMed: 32896329
DOI: 10.1016/bs.mcb.2020.06.009 -
Cells Dec 2020The transport of host proteins into and out of the nucleus is key to host function. However, nuclear transport is restricted by nuclear pores that perforate the nuclear... (Review)
Review
The transport of host proteins into and out of the nucleus is key to host function. However, nuclear transport is restricted by nuclear pores that perforate the nuclear envelope. Protein intrinsic disorder is an inherent feature of this selective transport barrier and is also a feature of the nuclear transport receptors that facilitate the active nuclear transport of cargo, and the nuclear transport signals on the cargo itself. Furthermore, intrinsic disorder is an inherent feature of viral proteins and viral strategies to disrupt host nucleocytoplasmic transport to benefit their replication. In this review, we highlight the role that intrinsic disorder plays in the nuclear transport of host and viral proteins. We also describe viral subversion mechanisms of the host nuclear transport machinery in which intrinsic disorder is a feature. Finally, we discuss nuclear import and export as therapeutic targets for viral infectious disease.
Topics: Active Transport, Cell Nucleus; Animals; Cell Nucleus; Humans; Protein Stability; Viral Proteins; Virus Replication
PubMed: 33321790
DOI: 10.3390/cells9122654 -
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 -
Proceedings of the National Academy of... May 2024Targeting proteins to specific subcellular destinations is essential in prokaryotes, eukaryotes, and the viruses that infect them. Chimalliviridae phages encapsulate...
Targeting proteins to specific subcellular destinations is essential in prokaryotes, eukaryotes, and the viruses that infect them. Chimalliviridae phages encapsulate their genomes in a nucleus-like replication compartment composed of the protein chimallin (ChmA) that excludes ribosomes and decouples transcription from translation. These phages selectively partition proteins between the phage nucleus and the bacterial cytoplasm. Currently, the genes and signals that govern selective protein import into the phage nucleus are unknown. Here, we identify two components of this protein import pathway: a species-specific surface-exposed region of a phage intranuclear protein required for nuclear entry and a conserved protein, PicA (Protein importer of chimalliviruses A), that facilitates cargo protein trafficking across the phage nuclear shell. We also identify a defective cargo protein that is targeted to PicA on the nuclear periphery but fails to enter the nucleus, providing insight into the mechanism of nuclear protein trafficking. Using CRISPRi-ART protein expression knockdown of PicA, we show that PicA is essential early in the chimallivirus replication cycle. Together, our results allow us to propose a multistep model for the Protein Import Chimallivirus pathway, where proteins are targeted to PicA by amino acids on their surface and then licensed by PicA for nuclear entry. The divergence in the selectivity of this pathway between closely related chimalliviruses implicates its role as a key player in the evolutionary arms race between competing phages and their hosts.
Topics: Viral Proteins; Bacteriophages; Protein Transport; Cell Nucleus; Virus Replication
PubMed: 38687783
DOI: 10.1073/pnas.2321190121 -
Current Genetics Aug 2020Iron is essential for nearly all aerobic organisms. One source of iron in nature is in the form of heme. Due to its critical physiological importance as a cofactor for... (Review)
Review
Iron is essential for nearly all aerobic organisms. One source of iron in nature is in the form of heme. Due to its critical physiological importance as a cofactor for several enzymes, organisms have evolved various means to secure heme for their needs. In the case of heme prototrophs, these organisms possess a highly conserved eight-step biosynthetic pathway. Another means used by many organisms is to acquire heme from external sources. As opposed to the knowledge of enzymes responsible for heme biosynthesis, the nature of the players and mechanisms involved in the acquisition of exogenous heme is limited. This review focuses on a description of newly discovered proteins that have novel functions in heme assimilation in the model organism Schizosaccharomyces pombe. This tractable model allows the use of the power of genetics to selectively block heme biosynthesis, setting conditions to investigate the mechanisms by which external heme is taken up by the cells. Studies have revealed that S. pombe possesses two independent heme uptake systems that require Shu1 and Str3, respectively. Heme-bound iron is captured by Shu1 at the cell surface, triggering its internalization to the vacuole with the aid of ubiquitinated proteins and the ESCRT machinery. In the case of the plasma membrane transporter Str3, it promotes cellular heme import in cells lacking Shu1. The discovery of these two pathways may contribute to gain novel insights into the mechanisms whereby fungi assimilate heme, which is an essentially biological process for their ability to invade and colonize new niches.
Topics: Animals; Endosomal Sorting Complexes Required for Transport; Fungi; Heme; Membrane Proteins; Schizosaccharomyces; Schizosaccharomyces pombe Proteins
PubMed: 32185489
DOI: 10.1007/s00294-020-01067-x -
Genes Jul 2021In human mitochondria, mtDNA encodes for only 13 proteins, all components of the OXPHOS system. The rest of the mitochondrial components, which make up approximately 99%... (Review)
Review
In human mitochondria, mtDNA encodes for only 13 proteins, all components of the OXPHOS system. The rest of the mitochondrial components, which make up approximately 99% of its proteome, are encoded in the nuclear genome, synthesized in cytosolic ribosomes and imported into mitochondria. Different import machineries translocate mitochondrial precursors, depending on their nature and the final destination inside the organelle. The proper and coordinated function of these molecular pathways is critical for mitochondrial homeostasis. Here, we will review molecular details about these pathways, which components have been linked to human disease and future perspectives on the field to expand the genetic landscape of mitochondrial diseases.
Topics: Cytosol; Humans; Mitochondria; Mitochondrial Membranes; Mitochondrial Proteins; Mutation; Protein Transport; Ribosomes
PubMed: 34356047
DOI: 10.3390/genes12071031 -
Open Biology Jul 2023Pathogenic variants in cause Troyer syndrome, characterized by lower extremity spasticity and weakness, short stature and cognitive impairment, and a severe...
Pathogenic variants in cause Troyer syndrome, characterized by lower extremity spasticity and weakness, short stature and cognitive impairment, and a severe mitochondrial impairment. Herein, we report the identification of a role of Spartin in nuclear-encoded mitochondrial proteins. biallelic missense variants were detected in a 5-year-old boy with short stature, developmental delay and muscle weakness with impaired walking distance. Patient-derived fibroblasts showed an altered mitochondrial network, decreased mitochondrial respiration, increased mitochondrial reactive oxygen species and altered Ca versus control cells. We investigated the mitochondrial import of nuclear-encoded proteins in these fibroblasts and in another cell model carrying a loss-of-function mutation. In both cell models the mitochondrial import was impaired, leading to a significant decrease in different proteins, including two key enzymes involved in CoQ10 (CoQ) synthesis, COQ7 and COQ9, with a severe reduction in CoQ content, versus control cells. CoQ supplementation restored cellular ATP levels to the same extent shown by the re-expression of wild-type SPART, suggesting CoQ treatment as a promising therapeutic approach for patients carrying mutations in .
Topics: Male; Humans; Child, Preschool; Ubiquinone; Cognitive Dysfunction; Nuclear Proteins; Energy Metabolism; Mitochondrial Proteins
PubMed: 37433330
DOI: 10.1098/rsob.230040 -
The Journal of Biological Chemistry May 2022The human mitochondrial outer membrane is biophysically unique as it is the only membrane possessing transmembrane β-barrel proteins (mitochondrial outer membrane... (Review)
Review
The human mitochondrial outer membrane is biophysically unique as it is the only membrane possessing transmembrane β-barrel proteins (mitochondrial outer membrane proteins, mOMPs) in the cell. The most vital of the three mOMPs is the core protein of the translocase of the outer mitochondrial membrane (TOM) complex. Identified first as MOM38 in Neurospora in 1990, the structure of Tom40, the core 19-stranded β-barrel translocation channel, was solved in 2017, after nearly three decades. Remarkably, the past four years have witnessed an exponential increase in structural and functional studies of yeast and human TOM complexes. In addition to being conserved across all eukaryotes, the TOM complex is the sole ATP-independent import machinery for nearly all of the ∼1000 to 1500 known mitochondrial proteins. Recent cryo-EM structures have provided detailed insight into both possible assembly mechanisms of the TOM core complex and organizational dynamics of the import machinery and now reveal novel regulatory interplay with other mOMPs. Functional characterization of the TOM complex using biochemical and structural approaches has also revealed mechanisms for substrate recognition and at least five defined import pathways for precursor proteins. In this review, we discuss the discovery, recently solved structures, molecular function, and regulation of the TOM complex and its constituents, along with the implications these advances have for alleviating human diseases.
Topics: Humans; Membrane Proteins; Mitochondria; Mitochondrial Membrane Transport Proteins; Mitochondrial Membranes; Mitochondrial Precursor Protein Import Complex Proteins; Mitochondrial Proteins; Protein Transport; Saccharomyces cerevisiae; Saccharomyces cerevisiae Proteins
PubMed: 35346689
DOI: 10.1016/j.jbc.2022.101870 -
The Plant Cell Aug 2022Photosynthesis and the biosynthesis of many important metabolites occur in chloroplasts. In these semi-autonomous organelles, the chloroplast genome encodes...
Photosynthesis and the biosynthesis of many important metabolites occur in chloroplasts. In these semi-autonomous organelles, the chloroplast genome encodes approximately 100 proteins. The remaining chloroplast proteins, close to 3,000, are encoded by nuclear genes whose products are translated in the cytosol and imported into chloroplasts. However, there is still no consensus on the composition of the protein import machinery including its motor proteins and on how newly imported chloroplast proteins are refolded. In this study, we have examined the function of orf2971, the largest chloroplast gene of Chlamydomonas reinhardtii. The depletion of Orf2971 causes the accumulation of protein precursors, partial proteolysis and aggregation of proteins, increased expression of chaperones and proteases, and autophagy. Orf2971 interacts with the TIC (translocon at the inner chloroplast envelope) complex, catalyzes ATP (adenosine triphosphate) hydrolysis, and associates with chaperones and chaperonins. We propose that Orf2971 is intimately connected to the protein import machinery and plays an important role in chloroplast protein quality control.
Topics: Cell Nucleus; Chloroplast Proteins; Chloroplasts; Molecular Chaperones; Plant Proteins; Protein Transport
PubMed: 35708659
DOI: 10.1093/plcell/koac180