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Science Immunology Jun 2023Hexokinase dissociation from mitochondria triggers calcium-induced oligomerization of VDAC within the outer mitochondrial membrane, leading to NLRP3 recruitment and... (Review)
Review
Hexokinase dissociation from mitochondria triggers calcium-induced oligomerization of VDAC within the outer mitochondrial membrane, leading to NLRP3 recruitment and inflammasome signaling (see related Research Article by Baik ).
Topics: NLR Family, Pyrin Domain-Containing 3 Protein; Mitochondria; Mitochondrial Membranes; Inflammasomes; Signal Transduction
PubMed: 37327323
DOI: 10.1126/sciimmunol.adh2967 -
Nature Feb 2024To coordinate cellular physiology, eukaryotic cells rely on the rapid exchange of molecules at specialized organelle-organelle contact sites. Endoplasmic...
To coordinate cellular physiology, eukaryotic cells rely on the rapid exchange of molecules at specialized organelle-organelle contact sites. Endoplasmic reticulum-mitochondrial contact sites (ERMCSs) are particularly vital communication hubs, playing key roles in the exchange of signalling molecules, lipids and metabolites. ERMCSs are maintained by interactions between complementary tethering molecules on the surface of each organelle. However, due to the extreme sensitivity of these membrane interfaces to experimental perturbation, a clear understanding of their nanoscale organization and regulation is still lacking. Here we combine three-dimensional electron microscopy with high-speed molecular tracking of a model organelle tether, Vesicle-associated membrane protein (VAMP)-associated protein B (VAPB), to map the structure and diffusion landscape of ERMCSs. We uncovered dynamic subdomains within VAPB contact sites that correlate with ER membrane curvature and undergo rapid remodelling. We show that VAPB molecules enter and leave ERMCSs within seconds, despite the contact site itself remaining stable over much longer time scales. This metastability allows ERMCSs to remodel with changes in the physiological environment to accommodate metabolic needs of the cell. An amyotrophic lateral sclerosis-associated mutation in VAPB perturbs these subdomains, likely impairing their remodelling capacity and resulting in impaired interorganelle communication. These results establish high-speed single-molecule imaging as a new tool for mapping the structure of contact site interfaces and reveal that the diffusion landscape of VAPB at contact sites is a crucial component of ERMCS homeostasis.
Topics: Humans; Amyotrophic Lateral Sclerosis; Endoplasmic Reticulum; Mitochondria; Mitochondrial Membranes; Signal Transduction; Vesicular Transport Proteins; Microscopy, Electron; Imaging, Three-Dimensional; Binding Sites; Diffusion; Time Factors; Mutation; Homeostasis; Movement
PubMed: 38267577
DOI: 10.1038/s41586-023-06956-y -
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 -
Open Biology Dec 2021Mitochondria are complex organelles with two membranes. Their architecture is determined by characteristic folds of the inner membrane, termed cristae. Recent studies in... (Review)
Review
Mitochondria are complex organelles with two membranes. Their architecture is determined by characteristic folds of the inner membrane, termed cristae. Recent studies in yeast and other organisms led to the identification of four major pathways that cooperate to shape cristae membranes. These include dimer formation of the mitochondrial ATP synthase, assembly of the mitochondrial contact site and cristae organizing system (MICOS), inner membrane remodelling by a dynamin-related GTPase (Mgm1/OPA1), and modulation of the mitochondrial lipid composition. In this review, we describe the function of the evolutionarily conserved machineries involved in mitochondrial cristae biogenesis with a focus on yeast and present current models to explain how their coordinated activities establish mitochondrial membrane architecture.
Topics: Animals; Humans; Mitochondria; Mitochondrial Membranes; Mitochondrial Proteins; Organelle Biogenesis; Protein Multimerization
PubMed: 34847778
DOI: 10.1098/rsob.210238 -
The Journal of Cell Biology Nov 2021Mitochondrial function is integrated with cellular status through the regulation of opposing mitochondrial fusion and division events. Here we uncover a link between...
Mitochondrial function is integrated with cellular status through the regulation of opposing mitochondrial fusion and division events. Here we uncover a link between mitochondrial dynamics and lipid metabolism by examining the cellular role of mitochondrial carrier homologue 2 (MTCH2). MTCH2 is a modified outer mitochondrial membrane carrier protein implicated in intrinsic cell death and in the in vivo regulation of fatty acid metabolism. Our data indicate that MTCH2 is a selective effector of starvation-induced mitochondrial hyperfusion, a cytoprotective response to nutrient deprivation. We find that MTCH2 stimulates mitochondrial fusion in a manner dependent on the bioactive lipogenesis intermediate lysophosphatidic acid. We propose that MTCH2 monitors flux through the lipogenesis pathway and transmits this information to the mitochondrial fusion machinery to promote mitochondrial elongation, enhanced energy production, and cellular survival under homeostatic and starvation conditions. These findings will help resolve the roles of MTCH2 and mitochondria in tissue-specific lipid metabolism in animals.
Topics: Animals; Apoptosis; COS Cells; Carrier Proteins; Cell Line; Cell Line, Tumor; Chlorocebus aethiops; HCT116 Cells; Humans; Lipid Metabolism; Lipogenesis; Mitochondria; Mitochondrial Dynamics; Mitochondrial Membrane Transport Proteins; Mitochondrial Membranes; Mitochondrial Proteins
PubMed: 34586346
DOI: 10.1083/jcb.202103122 -
Cell Reports Apr 2021During mitochondrial fission, key molecular and cellular factors assemble on the outer mitochondrial membrane, where they coordinate to generate constriction....
During mitochondrial fission, key molecular and cellular factors assemble on the outer mitochondrial membrane, where they coordinate to generate constriction. Constriction sites can eventually divide or reverse upon disassembly of the machinery. However, a role for membrane tension in mitochondrial fission, although speculated, has remained undefined. We capture the dynamics of constricting mitochondria in mammalian cells using live-cell structured illumination microscopy (SIM). By analyzing the diameters of tubules that emerge from mitochondria and implementing a fluorescence lifetime-based mitochondrial membrane tension sensor, we discover that mitochondria are indeed under tension. Under perturbations that reduce mitochondrial tension, constrictions initiate at the same rate, but are less likely to divide. We propose a model based on our estimates of mitochondrial membrane tension and bending energy in living cells which accounts for the observed probability distribution for mitochondrial constrictions to divide.
Topics: Animals; Biomechanical Phenomena; COS Cells; Chlorocebus aethiops; Cytoskeleton; Dynamins; Electron Transport Complex IV; Gene Expression; Genes, Reporter; Green Fluorescent Proteins; Humans; Luminescent Proteins; Mitochondria; Mitochondrial Dynamics; Mitochondrial Membranes; Surface Tension; Transfection; Transgenes; Red Fluorescent Protein
PubMed: 33852852
DOI: 10.1016/j.celrep.2021.108947 -
Nature Mar 2023Mitochondrial energy conversion requires an intricate architecture of the inner mitochondrial membrane. Here we show that a supercomplex containing all four respiratory...
Mitochondrial energy conversion requires an intricate architecture of the inner mitochondrial membrane. Here we show that a supercomplex containing all four respiratory chain components contributes to membrane curvature induction in ciliates. We report cryo-electron microscopy and cryo-tomography structures of the supercomplex that comprises 150 different proteins and 311 bound lipids, forming a stable 5.8-MDa assembly. Owing to subunit acquisition and extension, complex I associates with a complex IV dimer, generating a wedge-shaped gap that serves as a binding site for complex II. Together with a tilted complex III dimer association, it results in a curved membrane region. Using molecular dynamics simulations, we demonstrate that the divergent supercomplex actively contributes to the membrane curvature induction and tubulation of cristae. Our findings highlight how the evolution of protein subunits of respiratory complexes has led to the I-II-III-IV supercomplex that contributes to the shaping of the bioenergetic membrane, thereby enabling its functional specialization.
Topics: Cryoelectron Microscopy; Electron Transport; Electron Transport Complex III; Electron Transport Complex IV; Mitochondria; Mitochondrial Membranes; Electron Transport Complex II; Electron Transport Complex I; Protein Multimerization; Protein Subunits; Molecular Dynamics Simulation; Binding Sites; Evolution, Molecular
PubMed: 36949187
DOI: 10.1038/s41586-023-05817-y -
Nature Dec 2019The most frequently mutated oncogene in cancer is KRAS, which uses alternative fourth exons to generate two gene products (KRAS4A and KRAS4B) that differ only in their...
The most frequently mutated oncogene in cancer is KRAS, which uses alternative fourth exons to generate two gene products (KRAS4A and KRAS4B) that differ only in their C-terminal membrane-targeting region. Because oncogenic mutations occur in exons 2 or 3, two constitutively active KRAS proteins-each capable of transforming cells-are encoded when KRAS is activated by mutation. No functional distinctions among the splice variants have so far been established. Oncogenic KRAS alters the metabolism of tumour cells in several ways, including increased glucose uptake and glycolysis even in the presence of abundant oxygen (the Warburg effect). Whereas these metabolic effects of oncogenic KRAS have been explained by transcriptional upregulation of glucose transporters and glycolytic enzymes, it is not known whether there is direct regulation of metabolic enzymes. Here we report a direct, GTP-dependent interaction between KRAS4A and hexokinase 1 (HK1) that alters the activity of the kinase, and thereby establish that HK1 is an effector of KRAS4A. This interaction is unique to KRAS4A because the palmitoylation-depalmitoylation cycle of this RAS isoform enables colocalization with HK1 on the outer mitochondrial membrane. The expression of KRAS4A in cancer may drive unique metabolic vulnerabilities that can be exploited therapeutically.
Topics: Allosteric Regulation; Animals; Cell Line, Tumor; Enzyme Activation; Glycolysis; Guanosine Triphosphate; Hexokinase; Humans; In Vitro Techniques; Isoenzymes; Lipoylation; Male; Mice; Mitochondria; Mitochondrial Membranes; Neoplasms; Protein Binding; Protein Transport; Proto-Oncogene Proteins p21(ras)
PubMed: 31827279
DOI: 10.1038/s41586-019-1832-9 -
Biochimica Et Biophysica Acta.... Jan 2021Outer membrane proteins integrate mitochondria into the cellular environment. They warrant exchange of small molecules like metabolites and ions, transport proteins into... (Review)
Review
Outer membrane proteins integrate mitochondria into the cellular environment. They warrant exchange of small molecules like metabolites and ions, transport proteins into mitochondria, form contact sites to other cellular organelles for lipid exchange, constitute a signaling platform for apoptosis and inflammation and mediate organelle fusion and fission. The outer membrane contains two types of integral membrane proteins. Proteins with a transmembrane β-barrel structure and proteins with a single or multiple α-helical membrane spans. All outer membrane proteins are produced on cytosolic ribosomes and imported into the target organelle. Precursors of β-barrel and α-helical proteins are transported into the outer membrane via distinct import routes. The translocase of the outer membrane (TOM complex) transports β-barrel precursors across the outer membrane and the sorting and assembly machinery (SAM complex) inserts them into the target membrane. The mitochondrial import (MIM) complex constitutes the major integration site for α-helical embedded proteins. The import of some MIM-substrates involves TOM receptors, while others are imported in a TOM-independent manner. Remarkably, TOM, SAM and MIM complexes dynamically interact to import a large set of different proteins and to coordinate their assembly into protein complexes. Thus, protein import into the mitochondrial outer membrane involves a dynamic platform of protein translocases.
Topics: Animals; Humans; Membrane Transport Proteins; Mitochondria; Mitochondrial Membranes; Mitochondrial Proteins; Protein Transport
PubMed: 33035511
DOI: 10.1016/j.bbabio.2020.148323 -
Proceedings of the National Academy of... Jul 2023Cardiolipin (CL) is an essential phospholipid for mitochondrial structure and function. Here, we present a small mitochondrial protein, NERCLIN, as a negative regulator...
Cardiolipin (CL) is an essential phospholipid for mitochondrial structure and function. Here, we present a small mitochondrial protein, NERCLIN, as a negative regulator of CL homeostasis and mitochondrial ultrastructure. Primate-specific NERCLIN is expressed ubiquitously from the locus on a tightly regulated low level. NERCLIN overexpression severely disrupts mitochondrial cristae structure and induces mitochondrial fragmentation. Proximity labeling and immunoprecipitation analysis suggested interactions of NERCLIN with CL synthesis and prohibitin complexes on the matrix side of the inner mitochondrial membrane. Lipid analysis indicated that NERCLIN regulates mitochondrial CL content. Furthermore, NERCLIN is responsive to heat stress ensuring OPA1 processing and cell survival. Thus, we propose that NERCLIN contributes to the stress-induced adaptation of mitochondrial dynamics. Our findings add NERCLIN to the group of recently identified small mitochondrial proteins with important regulatory functions.
Topics: Animals; Mitochondrial Proteins; Cardiolipins; Mitochondria; Mitochondrial Membranes; Homeostasis
PubMed: 37463214
DOI: 10.1073/pnas.2210599120