RESUMEN
Brown adipose tissue (BAT) is best known for thermogenesis. Rodent studies demonstrated that enhanced BAT thermogenesis is tightly associated with increased energy expenditure, reduced body weight, and improved glucose homeostasis. However, human BAT is protective against type 2 diabetes, independent of body weight. The mechanism underlying this dissociation remains unclear. Here, we report that impaired mitochondrial catabolism of branched-chain amino acids (BCAAs) in BAT, by deleting mitochondrial BCAA carriers (MBCs), caused systemic insulin resistance without affecting energy expenditure and body weight. Brown adipocytes catabolized BCAA in the mitochondria as nitrogen donors for the biosynthesis of non-essential amino acids and glutathione. Impaired mitochondrial BCAA-nitrogen flux in BAT resulted in increased oxidative stress, decreased hepatic insulin signaling, and decreased circulating BCAA-derived metabolites. A high-fat diet attenuated BCAA-nitrogen flux and metabolite synthesis in BAT, whereas cold-activated BAT enhanced the synthesis. This work uncovers a metabolite-mediated pathway through which BAT controls metabolic health beyond thermogenesis.
Asunto(s)
Tejido Adiposo Pardo , Aminoácidos de Cadena Ramificada , Resistencia a la Insulina , Mitocondrias , Nitrógeno , Termogénesis , Tejido Adiposo Pardo/metabolismo , Animales , Aminoácidos de Cadena Ramificada/metabolismo , Ratones , Nitrógeno/metabolismo , Mitocondrias/metabolismo , Masculino , Humanos , Metabolismo Energético , Ratones Endogámicos C57BL , Estrés Oxidativo , Insulina/metabolismo , Dieta Alta en Grasa , Adipocitos Marrones/metabolismo , Transducción de SeñalRESUMEN
Members of the mitochondrial carrier family [solute carrier family 25 (SLC25)] transport nucleotides, amino acids, carboxylic acids, fatty acids, inorganic ions, and vitamins across the mitochondrial inner membrane. They are important for many cellular processes, such as oxidative phosphorylation of lipids and sugars, amino acid metabolism, macromolecular synthesis, ion homeostasis, cellular regulation, and differentiation. Here, we describe the functional elements of the transport mechanism of mitochondrial carriers, consisting of one central substrate-binding site and two gates with salt-bridge networks on either side of the carrier. Binding of the substrate during import causes three gate elements to rotate inward, forming the cytoplasmic network and closing access to the substrate-binding site from the intermembrane space. Simultaneously, three core elements rock outward, disrupting the matrix network and opening the substrate-binding site to the matrix side of the membrane. During export, substrate binding triggers conformational changes involving the same elements but operating in reverse.
Asunto(s)
Proteínas de Transporte de Membrana Mitocondrial/química , Proteínas de Transporte de Membrana Mitocondrial/genética , Proteínas de Transporte de Membrana Mitocondrial/metabolismo , Agrecanos/química , Agrecanos/genética , Agrecanos/metabolismo , Secuencia de Aminoácidos , Aminoácidos/química , Aminoácidos/metabolismo , Sitios de Unión , Transporte Biológico , Calcio/metabolismo , Cardiolipinas/metabolismo , Secuencia Conservada , Citoplasma/metabolismo , Humanos , Translocasas Mitocondriales de ADP y ATP/química , Translocasas Mitocondriales de ADP y ATP/metabolismo , Mutación , Conformación Proteica , Proteínas de Saccharomyces cerevisiae/química , Proteínas de Saccharomyces cerevisiae/metabolismoRESUMEN
Metabolic reprogramming is a key feature of many cancers, but how and when it contributes to tumorigenesis remains unclear. Here we demonstrate that metabolic reprogramming induced by mitochondrial fusion can be rate-limiting for immortalization of tumor-initiating cells (TICs) and trigger their irreversible dedication to tumorigenesis. Using single-cell transcriptomics, we find that Drosophila brain tumors contain a rapidly dividing stem cell population defined by upregulation of oxidative phosphorylation (OxPhos). We combine targeted metabolomics and in vivo genetic screening to demonstrate that OxPhos is required for tumor cell immortalization but dispensable in neural stem cells (NSCs) giving rise to tumors. Employing an in vivo NADH/NAD+ sensor, we show that NSCs precisely increase OxPhos during immortalization. Blocking OxPhos or mitochondrial fusion stalls TICs in quiescence and prevents tumorigenesis through impaired NAD+ regeneration. Our work establishes a unique connection between cellular metabolism and immortalization of tumor-initiating cells.
Asunto(s)
Neoplasias Encefálicas/metabolismo , Carcinogénesis/metabolismo , Transformación Celular Neoplásica/metabolismo , Dinámicas Mitocondriales , NAD/metabolismo , Células Madre Neoplásicas/metabolismo , Células-Madre Neurales/metabolismo , Fosforilación Oxidativa , Animales , Neoplasias Encefálicas/genética , Neoplasias Encefálicas/mortalidad , Neoplasias Encefálicas/patología , Carcinogénesis/genética , Carcinogénesis/patología , Transformación Celular Neoplásica/patología , Ciclo del Ácido Cítrico/genética , Biología Computacional , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Drosophila , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Glucólisis/genética , Espectrometría de Masas , Metabolómica , Microscopía Electrónica de Transmisión , Familia de Multigenes , Células-Madre Neurales/patología , Consumo de Oxígeno/genética , Interferencia de ARN , Especies Reactivas de Oxígeno/metabolismo , Análisis de la Célula Individual , Transcriptoma/genéticaRESUMEN
Directional transport of protons across an energy transducing membrane-proton pumping-is ubiquitous in biology. Bacteriorhodopsin (bR) is a light-driven proton pump that is activated by a buried all-trans retinal chromophore being photoisomerized to a 13-cis conformation. The mechanism by which photoisomerization initiates directional proton transport against a proton concentration gradient has been studied by a myriad of biochemical, biophysical, and structural techniques. X-ray free electron lasers (XFELs) have created new opportunities to probe the structural dynamics of bR at room temperature on timescales from femtoseconds to milliseconds using time-resolved serial femtosecond crystallography (TR-SFX). Wereview these recent developments and highlight where XFEL studies reveal new details concerning the structural mechanism of retinal photoisomerization and proton pumping. We also discuss the extent to which these insights were anticipated by earlier intermediate trapping studies using synchrotron radiation. TR-SFX will open up the field for dynamical studies of other proteins that are not naturally light-sensitive.
Asunto(s)
Bacteriorodopsinas/ultraestructura , Rayos Láser , Protones , Retinaldehído/química , Difracción de Rayos X/métodos , Bacteriorodopsinas/química , Bacteriorodopsinas/metabolismo , Cristalografía/instrumentación , Cristalografía/métodos , Halobacterium salinarum/química , Halobacterium salinarum/metabolismo , Transporte Iónico , Modelos Moleculares , Conformación Proteica , Retinaldehído/metabolismo , Sincrotrones/instrumentación , Rayos XRESUMEN
Mitochondrial ADP/ATP carriers transport ADP into the mitochondrial matrix for ATP synthesis, and ATP out to fuel the cell, by cycling between cytoplasmic-open and matrix-open states. The structure of the cytoplasmic-open state is known, but it has proved difficult to understand the transport mechanism in the absence of a structure in the matrix-open state. Here, we describe the structure of the matrix-open state locked by bongkrekic acid bound in the ADP/ATP-binding site at the bottom of the central cavity. The cytoplasmic side of the carrier is closed by conserved hydrophobic residues, and a salt bridge network, braced by tyrosines. Glycine and small amino acid residues allow close-packing of helices on the matrix side. Uniquely, the carrier switches between states by rotation of its three domains about a fulcrum provided by the substrate-binding site. Because these features are highly conserved, this mechanism is likely to apply to the whole mitochondrial carrier family. VIDEO ABSTRACT.
Asunto(s)
Mitocondrias/metabolismo , Translocasas Mitocondriales de ADP y ATP/metabolismo , Translocasas Mitocondriales de ADP y ATP/ultraestructura , Adenosina Difosfato/metabolismo , Adenosina Trifosfato/metabolismo , Secuencia de Aminoácidos , Sitios de Unión , Transporte Biológico , Ácido Bongcréquico/metabolismo , Citoplasma/metabolismo , Mitocondrias/fisiología , Translocasas Mitocondriales de ADP y ATP/fisiología , Proteínas de Transporte de Membrana Mitocondrial/metabolismo , Proteínas de Transporte de Membrana Mitocondrial/fisiología , Proteínas de Transporte de Membrana Mitocondrial/ultraestructura , Modelos Moleculares , Conformación Proteica , Estructura Secundaria de Proteína , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismoRESUMEN
We report a 100-million atom-scale model of an entire cell organelle, a photosynthetic chromatophore vesicle from a purple bacterium, that reveals the cascade of energy conversion steps culminating in the generation of ATP from sunlight. Molecular dynamics simulations of this vesicle elucidate how the integral membrane complexes influence local curvature to tune photoexcitation of pigments. Brownian dynamics of small molecules within the chromatophore probe the mechanisms of directional charge transport under various pH and salinity conditions. Reproducing phenotypic properties from atomistic details, a kinetic model evinces that low-light adaptations of the bacterium emerge as a spontaneous outcome of optimizing the balance between the chromatophore's structural integrity and robust energy conversion. Parallels are drawn with the more universal mitochondrial bioenergetic machinery, from whence molecular-scale insights into the mechanism of cellular aging are inferred. Together, our integrative method and spectroscopic experiments pave the way to first-principles modeling of whole living cells.
Asunto(s)
Células/metabolismo , Metabolismo Energético , Adaptación Fisiológica/efectos de la radiación , Adenosina Trifosfato/metabolismo , Benzoquinonas/metabolismo , Membrana Celular/metabolismo , Membrana Celular/efectos de la radiación , Células/efectos de la radiación , Cromatóforos/metabolismo , Citocromos c2/metabolismo , Difusión , Transporte de Electrón/efectos de la radiación , Metabolismo Energético/efectos de la radiación , Ambiente , Enlace de Hidrógeno , Cinética , Luz , Simulación de Dinámica Molecular , Fenotipo , Proteínas/metabolismo , Rhodobacter sphaeroides/fisiología , Rhodobacter sphaeroides/efectos de la radiación , Electricidad Estática , Estrés Fisiológico/efectos de la radiación , TemperaturaRESUMEN
Chronic kidney disease (CKD) affects >10% of the world population, with increasing prevalence in middle age. The risk for CKD is dependent on the number of functioning nephrons through the life cycle, and 50% of nephrons are lost through normal aging, revealing their vulnerability to internal and external stressors. Factors responsible for CKD remain poorly understood, with limited availability of biomarkers or effective therapy to slow progression. This review draws on the disciplines of evolutionary medicine and bioenergetics to account for the heterogeneous nephron injury that characterizes progressive CKD following episodes of acute kidney injury with incomplete recovery. The evolution of symbiosis in eukaryotes led to the efficiencies of oxidative phosphorylation and the rise of metazoa. Adaptations to ancestral environments are the products of natural selection that have shaped the mammalian nephron with its vulnerabilities to ischemic, hypoxic, and toxic injury. Reproductive fitness rather than longevity has served as the driver of evolution, constrained by available energy and its allocation to homeostatic responses through the life cycle. Metabolic plasticity has evolved in parallel with robustness necessary to preserve complex developmental programs, and adaptations that optimize survival through reproductive years can become maladaptive with aging, reflecting antagonistic pleiotropy. Consequently, environmental stresses promote trade-offs and mismatches that result in cell fate decisions that ultimately lead to nephron loss. Elucidation of the bioenergetic adaptations by the nephron to ancestral and contemporary environments may lead to the development of new biomarkers of kidney disease and new therapies to reduce the global burden of progressive CKD.
Asunto(s)
Riñón , Insuficiencia Renal Crónica , Persona de Mediana Edad , Animales , Humanos , Riñón/metabolismo , Nefronas/metabolismo , Insuficiencia Renal Crónica/epidemiología , Insuficiencia Renal Crónica/metabolismo , Envejecimiento , Metabolismo Energético , MamíferosRESUMEN
In mitochondria, the oxidation of nutrients is coupled to ATP synthesis by the generation of a protonmotive force across the mitochondrial inner membrane. In mammalian brown adipose tissue (BAT), uncoupling protein 1 (UCP1, SLC25A7), a member of the SLC25 mitochondrial carrier family, dissipates the protonmotive force by facilitating the return of protons to the mitochondrial matrix. This process short-circuits the mitochondrion, generating heat for non-shivering thermogenesis. Recent cryo-electron microscopy (cryo-EM) structures of human UCP1 have provided new molecular insights into the inhibition and activation of thermogenesis. Here, we discuss these structures, describing how purine nucleotides lock UCP1 in a proton-impermeable conformation and rationalizing potential conformational changes of this carrier in response to fatty acid activators that enable proton leak for thermogenesis.
Asunto(s)
Termogénesis , Proteína Desacopladora 1 , Humanos , Proteína Desacopladora 1/metabolismo , Animales , Mitocondrias/metabolismo , Tejido Adiposo Pardo/metabolismoRESUMEN
Members of the SLC25 mitochondrial carrier family link cytosolic and mitochondrial metabolism and support cellular maintenance and growth by transporting compounds across the mitochondrial inner membrane. Their monomeric or dimeric state and kinetic mechanism have been a matter of long-standing debate. It is believed by some that they exist as homodimers and transport substrates with a sequential kinetic mechanism, forming a ternary complex where both exchanged substrates are bound simultaneously. Some studies, in contrast, have provided evidence indicating that the mitochondrial ADP/ATP carrier (SLC25A4) functions as a monomer, has a single substrate binding site, and operates with a ping-pong kinetic mechanism, whereby ADP is imported before ATP is exported. Here we reanalyze the oligomeric state and kinetic properties of the human mitochondrial citrate carrier (SLC25A1), dicarboxylate carrier (SLC25A10), oxoglutarate carrier (SLC25A11), and aspartate/glutamate carrier (SLC25A13), all previously reported to be dimers with a sequential kinetic mechanism. We demonstrate that they are monomers, except for dimeric SLC25A13, and operate with a ping-pong kinetic mechanism in which the substrate import and export steps occur consecutively. These observations are consistent with a common transport mechanism, based on a functional monomer, in which a single central substrate-binding site is alternately accessible.
Asunto(s)
Transportadores de Ácidos Dicarboxílicos , Humanos , Cinética , Transportadores de Ácidos Dicarboxílicos/metabolismo , Transportadores de Ácidos Dicarboxílicos/genética , Mitocondrias/metabolismo , Mitocondrias/genética , Proteínas de Transporte de Membrana Mitocondrial/metabolismo , Proteínas de Transporte de Membrana Mitocondrial/genética , Multimerización de Proteína , Sistemas de Transporte de Aminoácidos Acídicos/metabolismo , Sistemas de Transporte de Aminoácidos Acídicos/genética , Proteínas de Transporte de Anión/metabolismo , Proteínas de Transporte de Anión/genética , Proteínas de Transporte de Anión/química , Proteínas Mitocondriales/metabolismo , Proteínas Mitocondriales/genética , Antiportadores/metabolismo , Antiportadores/genética , Antiportadores/química , Translocasas Mitocondriales de ADP y ATP/metabolismo , Translocasas Mitocondriales de ADP y ATP/genética , Transporte Biológico , Transportadores de Anión Orgánico/metabolismo , Transportadores de Anión Orgánico/genética , Transportadores de Anión Orgánico/química , Adenosina Trifosfato/metabolismo , Proteínas Portadoras , Proteínas de Transporte de MembranaRESUMEN
Mitochondrial dysfunction is a central hallmark of aging and energy transduction is a promising target for longevity interventions. New research suggests that interventions in how energy is transduced could benefit healthy longevity. Here, we propose using light as an alternative energy source to fuel mitochondria and increase metazoan lifespan.
RESUMEN
The mitochondrial electron transport chain complexes are organized into supercomplexes (SCs) of defined stoichiometry, which have been proposed to regulate electron flux via substrate channeling. We demonstrate that CoQ trapping in the isolated SC I+III2 limits complex (C)I turnover, arguing against channeling. The SC structure, resolved at up to 3.8 Å in four distinct states, suggests that CoQ oxidation may be rate limiting because of unequal access of CoQ to the active sites of CIII2. CI shows a transition between "closed" and "open" conformations, accompanied by the striking rotation of a key transmembrane helix. Furthermore, the state of CI affects the conformational flexibility within CIII2, demonstrating crosstalk between the enzymes. CoQ was identified at only three of the four binding sites in CIII2, suggesting that interaction with CI disrupts CIII2 symmetry in a functionally relevant manner. Together, these observations indicate a more nuanced functional role for the SCs.
Asunto(s)
Complejo III de Transporte de Electrones/química , Complejo I de Transporte de Electrón/química , Mitocondrias Cardíacas/enzimología , Animales , Cristalografía por Rayos X , Estructura Cuaternaria de Proteína , OvinosRESUMEN
Noise control, together with other regulatory functions facilitated by microRNAs (miRNAs), is believed to have played important roles in the evolution of multicellular eukaryotic organisms. miRNAs can dampen protein fluctuations via enhanced degradation of messenger RNA (mRNA), but this requires compensation by increased mRNA transcription to maintain the same expression levels. The overall mechanism is metabolically expensive, leading to questions about how it might have evolved in the first place. We develop a stochastic model of miRNA noise regulation, coupled with a detailed analysis of the associated metabolic costs. Additionally, we calculate binding free energies for a range of miRNA seeds, the short sequences which govern target recognition. We argue that natural selection may have fine-tuned the Michaelis-Menten constant [Formula: see text] describing miRNA-mRNA affinity and show supporting evidence from analysis of experimental data. [Formula: see text] is constrained by seed length, and optimal noise control (minimum protein variance at a given energy cost) is achievable for seeds of 6 to 7 nucleotides in length, the most commonly observed types. Moreover, at optimality, the degree of noise reduction approaches the theoretical bound set by the Wiener-Kolmogorov linear filter. The results illustrate how selective pressure toward energy efficiency has potentially shaped a crucial regulatory pathway in eukaryotes.
Asunto(s)
Eucariontes , MicroARNs , MicroARNs/genética , Proteínas Mutantes , ARN Mensajero , Metabolismo Energético/genéticaRESUMEN
Hydrogen sulfide exposure in moderate doses can induce profound but reversible hypometabolism in mammals. At a cellular level, H2S inhibits the electron transport chain (ETC), augments aerobic glycolysis, and glutamine-dependent carbon utilization via reductive carboxylation; however, the durability of these changes is unknown. We report that despite its volatility, H2S preconditioning increases P50(O2), the O2 pressure for half-maximal cellular respiration, and has pleiotropic effects on oxidative metabolism that persist up to 24 to 48 h later. Notably, cyanide, another complex IV inhibitor, does not induce this type of metabolic memory. Sulfide-mediated prolonged fractional inhibition of complex IV by H2S is modulated by sulfide quinone oxidoreductase, which commits sulfide to oxidative catabolism. Since induced hypometabolism can be beneficial in disease settings that involve insufficient or interrupted blood flow, our study has important implications for attenuating reperfusion-induced ischemic injury and/or prolonging the shelf life of biologics like platelets.
Asunto(s)
Sulfuro de Hidrógeno , Daño por Reperfusión , Animales , Sulfuro de Hidrógeno/farmacología , Sulfuro de Hidrógeno/metabolismo , Sulfuros , Oxidación-Reducción , Mamíferos/metabolismoRESUMEN
Proton-powered c-ring rotation in mitochondrial ATP synthase is crucial to convert the transmembrane protonmotive force into torque to drive the synthesis of adenosine triphosphate (ATP). Capitalizing on recent cryo-EM structures, we aim at a structural and energetic understanding of how functional directional rotation is achieved. We performed multi-microsecond atomistic simulations to determine the free energy profiles along the c-ring rotation angle before and after the arrival of a new proton. Our results reveal that rotation proceeds by dynamic sliding of the ring over the a-subunit surface, during which interactions with conserved polar residues stabilize distinct intermediates. Ordered water chains line up for a Grotthuss-type proton transfer in one of these intermediates. After proton transfer, a high barrier prevents backward rotation and an overall drop in free energy favors forward rotation, ensuring the directionality of c-ring rotation required for the thermodynamically disfavored ATP synthesis. The essential arginine of the a-subunit stabilizes the rotated configuration through a salt bridge with the c-ring. Overall, we describe a complete mechanism for the rotation step of the ATP synthase rotor, thereby illuminating a process critical to all life at atomic resolution.
Asunto(s)
ATPasas de Translocación de Protón Mitocondriales , Protones , ATPasas de Translocación de Protón Mitocondriales/metabolismo , Conformación Proteica , Adenosina Trifosfato , Rotación , ATPasas de Translocación de Protón/metabolismoRESUMEN
Cellular metabolism must adapt to changing demands to enable homeostasis. During immune responses or cancer metastasis, cells leading migration into challenging environments require an energy boost, but what controls this capacity is unclear. Here, we study a previously uncharacterized nuclear protein, Atossa (encoded by CG9005), which supports macrophage invasion into the germband of Drosophila by controlling cellular metabolism. First, nuclear Atossa increases mRNA levels of Porthos, a DEAD-box protein, and of two metabolic enzymes, lysine-α-ketoglutarate reductase (LKR/SDH) and NADPH glyoxylate reductase (GR/HPR), thus enhancing mitochondrial bioenergetics. Then Porthos supports ribosome assembly and thereby raises the translational efficiency of a subset of mRNAs, including those affecting mitochondrial functions, the electron transport chain, and metabolism. Mitochondrial respiration measurements, metabolomics, and live imaging indicate that Atossa and Porthos power up OxPhos and energy production to promote the forging of a path into tissues by leading macrophages. Since many crucial physiological responses require increases in mitochondrial energy output, this previously undescribed genetic program may modulate a wide range of cellular behaviors.
Asunto(s)
Drosophila , Sacaropina Deshidrogenasas , Animales , Drosophila/metabolismo , Metabolismo Energético , Macrófagos/metabolismo , Mitocondrias/metabolismo , ARN Mensajero/metabolismo , Sacaropina Deshidrogenasas/genética , Sacaropina Deshidrogenasas/metabolismoRESUMEN
The electron-conducting circuitry of life represents an as-yet untapped resource of exquisite, nanoscale biomolecular engineering. Here, we report the characterization and structure of a de novo diheme "maquette" protein, 4D2, which we subsequently use to create an expanded, modular platform for heme protein design. A well-folded monoheme variant was created by computational redesign, which was then utilized for the experimental validation of continuum electrostatic redox potential calculations. This demonstrates how fundamental biophysical properties can be predicted and fine-tuned. 4D2 was then extended into a tetraheme helical bundle, representing a 7 nm molecular wire. Despite a molecular weight of only 24 kDa, electron cryomicroscopy illustrated a remarkable level of detail, indicating the positioning of the secondary structure and the heme cofactors. This robust, expressible, highly thermostable and readily designable modular platform presents a valuable resource for redox protein design and the future construction of artificial electron-conducting circuitry.
Asunto(s)
Hemoproteínas , Biofisica , Microscopía por Crioelectrón , Electrones , Oxidación-ReducciónRESUMEN
F1-ATPase is a motor protein that couples the rotation of its rotary [Formula: see text] subunit with ATP synthesis or hydrolysis. Single-molecule experiments indicate that nucleotide binding and release events occur almost simultaneously during the synthesis cycle, allowing the energy gain due to spontaneous binding of ADP to one catalytic [Formula: see text] subunit to be directly harnessed for driving the release of ATP from another rather than being dissipated as heat. Here, we examine the unknown mechanism of this coupling that is critical for an exceptionally high mechanochemical efficiency of F1-ATPase by means of all-atom free-energy simulations. We find that nondissipative and kinetically fast progression of the motor in the synthesis direction requires a concerted conformational change involving the closure of the ADP-binding [Formula: see text] subunit followed by the gradual opening of the ATP-releasing [Formula: see text] subunit over the course of the 30 to 40° rotary substep of the [Formula: see text] subunit. This rotary substep, preceding the ATP-dependent metastable state, allows for the recovery of a large portion of the ADP binding energy in the conformation of ATP-bound [Formula: see text] that gradually adopts the low-affinity conformation, captured also by the recent cryo-EM structure of this elusive state. The release of ATP from this nearly open conformation leads to its further opening, which enables the progression of the motor to the next catalytic metastable state. Our simulations explain this energy conversion mechanism in terms of intersubunit and ligand-protein interactions.
Asunto(s)
Adenosina Trifosfato , ATPasas de Translocación de Protón , ATPasas de Translocación de Protón/metabolismo , Catálisis , Conformación Proteica , Termodinámica , Adenosina Trifosfato/metabolismo , Hidrólisis , CinéticaRESUMEN
Mitochondria provide essential metabolites and adenosine triphosphate (ATP) for the regulation of energy homeostasis. For instance, liver mitochondria are a vital source of gluconeogenic precursors under a fasted state. However, the regulatory mechanisms at the level of mitochondrial membrane transport are not fully understood. Here, we report that a liver-specific mitochondrial inner-membrane carrier SLC25A47 is required for hepatic gluconeogenesis and energy homeostasis. Genome-wide association studies found significant associations between SLC25A47 and fasting glucose, HbA1c, and cholesterol levels in humans. In mice, we demonstrated that liver-specific depletion of SLC25A47 impaired hepatic gluconeogenesis selectively from lactate, while significantly enhancing whole-body energy expenditure and the hepatic expression of FGF21. These metabolic changes were not a consequence of general liver dysfunction because acute SLC25A47 depletion in adult mice was sufficient to enhance hepatic FGF21 production, pyruvate tolerance, and insulin tolerance independent of liver damage and mitochondrial dysfunction. Mechanistically, SLC25A47 depletion leads to impaired hepatic pyruvate flux and malate accumulation in the mitochondria, thereby restricting hepatic gluconeogenesis. Together, the present study identified a crucial node in the liver mitochondria that regulates fasting-induced gluconeogenesis and energy homeostasis.
Asunto(s)
Estudio de Asociación del Genoma Completo , Gluconeogénesis , Humanos , Ratones , Animales , Gluconeogénesis/fisiología , Glucosa/metabolismo , Hígado/metabolismo , Metabolismo Energético/fisiología , Piruvatos/metabolismoRESUMEN
Epulopiscium spp. are the largest known heterotrophic bacteria; a large cigar-shaped individual is a million times the volume of Escherichia coli. To better understand the metabolic potential and relationship of Epulopiscium sp. type B with its host Naso tonganus, we generated a high-quality draft genome from a population of cells taken from a single fish. We propose the name Candidatus Epulopiscium viviparus to describe populations of this best-characterized Epulopiscium species. Metabolic reconstruction reveals more than 5% of the genome codes for carbohydrate active enzymes, which likely degrade recalcitrant host-diet algal polysaccharides into substrates that may be fermented to acetate, the most abundant short-chain fatty acid in the intestinal tract. Moreover, transcriptome analyses and the concentration of sodium ions in the host intestinal tract suggest that the use of a sodium motive force (SMF) to drive ATP synthesis and flagellar rotation is integral to symbiont metabolism and cellular biology. In natural populations, genes encoding both F-type and V-type ATPases and SMF generation via oxaloacetate decarboxylation are among the most highly expressed, suggesting that ATPases synthesize ATP and balance ion concentrations across the cell membrane. High expression of these and other integral membrane proteins may allow for the growth of its extensive intracellular membrane system. Further, complementary metabolism between microbe and host is implied with the potential provision of nitrogen and B vitamins to reinforce this nutritional symbiosis. The few features shared by all bacterial behemoths include extreme polyploidy, polyphosphate synthesis, and thus far, they have all resisted cultivation in the lab.
Asunto(s)
Sodio , ATPasas de Translocación de Protón Vacuolares , Animales , Sodio/metabolismo , Bacterias/metabolismo , Clostridiales/metabolismo , ATPasas de Translocación de Protón Vacuolares/metabolismo , Adenosina Trifosfato/metabolismoRESUMEN
The respiratory chain in aerobic organisms is composed of a number of membrane-bound protein complexes that link electron transfer to proton translocation across the membrane. In mitochondria, the final electron acceptor, complex IV (CIV), receives electrons from dimeric complex III (CIII2), via a mobile electron carrier, cytochrome c. In the present study, we isolated the CIII2CIV supercomplex from the fission yeast Schizosaccharomyces pombe and determined its structure with bound cyt. c using single-particle electron cryomicroscopy. A respiratory supercomplex factor 2 was found to be bound at CIV distally positioned in the supercomplex. In addition to the redox-active metal sites, we found a metal ion, presumably Zn2+, coordinated in the CIII subunit Cor1, which is encoded by the same gene (qcr1) as the mitochondrial-processing peptidase subunit ß. Our data show that the isolated CIII2CIV supercomplex displays proteolytic activity suggesting a dual role of CIII2 in S. pombe. As in the supercomplex from S. cerevisiae, subunit Cox5 of CIV faces towards one CIII monomer, but in S. pombe, the two complexes are rotated relative to each other by ~45°. This orientation yields equal distances between the cyt. c binding sites at CIV and at each of the two CIII monomers. The structure shows cyt. c bound at four positions, but only along one of the two symmetrical branches. Overall, this combined structural and functional study reveals the integration of peptidase activity with the CIII2 respiratory system and indicates a two-dimensional cyt. c diffusion mechanism within the CIII2-CIV supercomplex.