RESUMO
Plastids are organelles delineated by two envelopes playing important roles in different cellular processes such as energy production or lipid biosynthesis. To regulate their biogenesis and their function, plastids have to communicate with other cellular compartments. This communication can be mediated by metabolites, signaling molecules, and by the establishment of direct contacts between the plastid envelope and other organelles such as the endoplasmic reticulum, mitochondria, peroxisomes, plasma membrane, and the nucleus. These interactions are highly dynamic and respond to different biotic and abiotic stresses. However, the mechanisms involved in the formation of plastid-organelle contact sites and their functions are still far from being understood. In this chapter, we summarize our current knowledge about plastid contact sites and their role in the regulation of plastid biogenesis and function.
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Retículo Endoplasmático , Plastídeos , Plastídeos/metabolismo , Retículo Endoplasmático/metabolismo , Mitocôndrias/metabolismo , Membrana Celular/metabolismo , Peroxissomos/metabolismoRESUMO
Plastids are organelles playing fundamental roles in different cellular processes such as energy metabolism or lipid biosynthesis. To fulfill their biogenesis and their function in the cell, plastids have to communicate with other cellular compartments. This communication can be mediated by the establishment of direct contact sites between plastids envelop and other organelles. These contacts are dynamic structures regulated in response to stress. For example, during phosphate (Pi) starvation, the number of contact sites between plastids and mitochondria significantly increases. In this situation, these contacts play an important role in the transfer of galactoglycerolipids from plastids to mitochondria. Recently, Pi starvation stress was used to identify key proteins involved in the traffic of galactoglycerolipids from plastids to mitochondria in Arabidopsis thaliana. A mitochondrial lipoprotein complex called MTL (Mitochondrial Transmembrane Lipoprotein) was identified. This complex contains mitochondrial proteins but also proteins located in the plastid envelope, suggesting its presence at the plastid-mitochondria junction. This chapter describes the protocol to isolate the MTL complex by clear-native polyacrylamide gel electrophoresis (CN-PAGE) from the mitochondrial fraction of Arabidopsis cell cultures and the methods to study different features of this complex.
Assuntos
Proteínas de Arabidopsis , Arabidopsis , Mitocôndrias/metabolismo , Membranas Mitocondriais/metabolismo , Arabidopsis/metabolismo , Plastídeos/metabolismo , Proteínas de Arabidopsis/metabolismo , Lipoproteínas/metabolismoRESUMO
Lipid transport proteins (LTPs) facilitate nonvesicular lipid exchange between cellular compartments and have critical roles in lipid homeostasis1. A new family of bridge-like LTPs (BLTPs) is thought to form lipid-transporting conduits between organelles2. One, BLTP2, is conserved across species but its function is not known. Here, we show that BLTP2 and its homolog directly regulate plasma membrane (PM) fluidity by increasing the phosphatidylethanolamine (PE) level in the PM. BLTP2 localizes to endoplasmic reticulum (ER)-PM contact sites34, 5, suggesting it transports PE from the ER to the PM. We find BLTP2 works in parallel with another pathway that regulates intracellular PE distribution and PM fluidity6, 7. BLTP2 expression correlates with breast cancer aggressiveness8-10. We found BLTP2 facilitates growth of a human cancer cell line and sustains its aggressiveness in an in vivo model of metastasis, suggesting maintenance of PM fluidity by BLTP2 may be critical for tumorigenesis in humans.
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VPS13 is a lipid transfer protein family conserved among Eukaryotes and playing roles in fundamental processes involving vesicular transport and membrane expansion including autophagy and organelle biogenesis. VPS13 folds into a long hydrophobic tunnel, allowing lipid transport, decorated by distinct domains involved in protein localization and regulation. Whereas VPS13 organization and function have been extensively studied in yeast and mammals, information in organisms originating from primary endosymbiosis is scarce. In the higher plant Arabidopsis thaliana, four paralogs, AtVPS13S, X, M1, and M2, were identified, AtVPS13S playing a role in the regulation of root growth, cell patterning, and reproduction. In this work, we performed phylogenetic, as well as domain and structural modeling of VPS13 proteins in Archaeplastida in order to understand their general organization and evolutionary history. We confirmed the presence of human VPS13B orthologues in some phyla and described two new VPS13 families presenting a particular domain arrangement: VPS13R in Rhodophytes and VPS13Y in Chlorophytes and Streptophytes. By focusing on Viridiplantae, we were able to draw the evolutionary history of these proteins made by multiple gene gains and duplications as well as domain rearrangements. We showed that some Chlorophytes have only three (AtVPS13M, S, Y) whereas some Charophytes have up to six VPS13 paralogs (AtVPS13M1, M2, S, Y, X, B). We also highlighted specific structural features of VPS13M and X paralogs. This study reveals the complex evolution of VPS13 family and opens important perspectives for their functional characterization in photosynthetic organisms.
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Despite decades of extensive research, mitochondrial lipid transport is a process far from fully understood. In this issue, Sassano et al. (2023. J. Cell Biol.https://doi.org/10.1083/jcb.202206008) identified a new complex, composed of E-Syt1 and PERK, which mediates lipid transport at ER-mitochondria contact sites and regulates mitochondrial functions in human cells.
Assuntos
Metabolismo dos Lipídeos , Mitocôndrias , Membranas Mitocondriais , Humanos , Transporte Biológico , Mitocôndrias/metabolismo , Membranas Mitocondriais/metabolismo , Sinaptotagmina I/metabolismo , eIF-2 Quinase , Retículo Endoplasmático/metabolismo , Biogênese de OrganelasRESUMO
Thraustochytrids are marine protists that naturally accumulate triacylglycerol with long chains of polyunsaturated fatty acids, such as ω3-docosahexaenoic acid (DHA). They represent a sustainable response to the increasing demand for these "essential" fatty acids (FAs). Following an attempt to transform a strain of Aurantiochytrium limacinum, we serendipitously isolated a clone that did not incorporate any recombinant DNA but contained two to three times more DHA than the original strain. Metabolic analyses indicated a deficit in FA catabolism. However, whole transcriptome analysis did not show down-regulation of genes involved in FA catabolism. Genome sequencing revealed extensive DNA deletion in one allele encoding a putative peroxisomal adenylate transporter. Phylogenetic analyses and yeast complementation experiments confirmed the gene as a peroxisomal adenylate nucleotide transporter (AlANT1), homologous to yeast ScANT1 and plant peroxisomal adenylate nucleotide carrier AtPNC genes. In yeast and plants, a deletion of the peroxisomal adenylate transporter inhibits FA breakdown and induces FA accumulation, a phenotype similar to that described here. In response to this metabolic event, several compensatory mechanisms were observed. In particular, genes involved in FA biosynthesis were upregulated, also contributing to the high FA accumulation. These results support AlANT1 as a promising target for enhancing DHA production in Thraustochytrids.
Assuntos
Trifosfato de Adenosina/metabolismo , Ácidos Graxos/metabolismo , Mutação/genética , Óleos/metabolismo , Peroxissomos/metabolismo , Estramenópilas/metabolismo , Transporte Biológico , Perfilação da Expressão Gênica , Genoma , Modelos Biológicos , Filogenia , Estramenópilas/genética , Estramenópilas/crescimento & desenvolvimento , Estramenópilas/ultraestrutura , Transcriptoma/genéticaRESUMO
Diverse classes of lipids are found in cell membranes, the major ones being glycerolipids, sphingolipids, and sterols. In eukaryotic cells, each organelle has a specific lipid composition, which defines its identity and regulates its biogenesis and function. For example, glycerolipids are present in all membranes, whereas sphingolipids and sterols are mostly enriched in the plasma membrane. In addition to phosphoglycerolipids, plants also contain galactoglycerolipids, a family of glycerolipids present mainly in chloroplasts and playing an important role in photosynthesis. During phosphate starvation, galactoglycerolipids are also found in large amounts in other organelles, illustrating the dynamic nature of membrane lipid composition. Thus, it is important to determine the lipid composition of each organelle, as analyses performed on total cells do not represent the specific changes occurring at the organelle level. This task requires the optimization of standard protocols to isolate organelles with high yield and low contamination by other cellular fractions. In this chapter, we describe a protocol to isolate mitochondria from Arabidopsis thaliana cell cultures to perform lipidomic analysis.
Assuntos
Cromatografia em Camada Fina/métodos , Lipídeos/isolamento & purificação , Mitocôndrias/química , Arabidopsis/metabolismo , Proteínas de Arabidopsis/isolamento & purificação , Proteínas de Arabidopsis/metabolismo , Cloroplastos/metabolismo , Metabolismo dos Lipídeos/fisiologia , Lipídeos/análise , Lipídeos de Membrana/metabolismo , Mitocôndrias/metabolismo , Organelas/metabolismo , Fotossíntese , Células Vegetais/metabolismo , Plantas/química , Plantas/metabolismo , Espectrometria de Massas em Tandem/métodosRESUMO
The metabolic pathways of glycerolipids are well described in cells containing chloroplasts limited by a two-membrane envelope but not in cells containing plastids limited by four membranes, including heterokonts. Fatty acids (FAs) produced in the plastid, palmitic and palmitoleic acids (16:0 and 16:1), are used in the cytosol for the synthesis of glycerolipids via various routes, requiring multiple acyl-Coenzyme A (CoA) synthetases (ACS). Here, we characterized an ACS of the Bubblegum subfamily in the photosynthetic eukaryote Microchloropsis gaditana, an oleaginous heterokont used for the production of lipids for multiple applications. Genome engineering with TALE-N allowed the generation of MgACSBG point mutations, but no knockout was obtained. Point mutations triggered an overall decrease of 16:1 in lipids, a specific increase of unsaturated 18-carbon acyls in phosphatidylcholine and decrease of 20-carbon acyls in the betaine lipid diacylglyceryl-trimethyl-homoserine. The profile of acyl-CoAs highlighted a decrease in 16:1-CoA and 18:3-CoA. Structural modeling supported that mutations affect accessibility of FA to the MgACSBG reaction site. Expression in yeast defective in acyl-CoA biosynthesis further confirmed that point mutations affect ACSBG activity. Altogether, this study supports a critical role of heterokont MgACSBG in the production of 16:1-CoA and 18:3-CoA. In M. gaditana mutants, the excess saturated and monounsaturated FAs were diverted to triacylglycerol, thus suggesting strategies to improve the oil content in this microalga.
Assuntos
Coenzima A Ligases/metabolismo , Cianobactérias/genética , Cianobactérias/fisiologia , Ácidos Graxos/genética , Ácidos Graxos/metabolismo , Redes e Vias Metabólicas , Fotossíntese/fisiologia , Coenzima A Ligases/genéticaRESUMO
The biogenesis of cellular membranes involves an important traffic of lipids from their site of synthesis to their final destination. Lipid transfer can be mediated by vesicular or non-vesicular pathways. The non-vesicular pathway requires the close apposition of two membranes to form a functional platform, called membrane contact sites (MCSs), where lipids are exchanged. These last decades, MCSs have been observed between virtually all organelles and a role in lipid transfer has been demonstrated for some of them. In plants, the lipid composition of membranes is highly dynamic and can be drastically modified in response to environmental changes. This highlights the importance of understanding the mechanisms involved in the regulation of membrane lipid homeostasis in plants. This review summarizes our current knowledge about the non-vesicular transport of lipids at MCSs in plants and its regulation during stress.
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Membrane biogenesis requires an extensive traffic of lipids between different cell compartments. Two main pathways, the vesicular and non-vesicular pathways, are involved in such a process. Whereas the mechanisms involved in vesicular trafficking are well understood, fewer is known about non-vesicular lipid trafficking, particularly in plants. This pathway involves the direct exchange of lipids at membrane contact sites (MCSs) between organelles. In plants, an extensive traffic of the chloroplast-synthesized digalactosyldiacylglycerol (DGDG) to mitochondria occurs during phosphate starvation. This lipid exchange occurs by non-vesicular trafficking pathways at MCSs between mitochondria and plastids. By a biochemical approach, a mitochondrial lipoprotein super-complex called MTL (Mitochondrial Transmembrane Lipoprotein complex) involved in mitochondria lipid trafficking has been identified in Arabidopsis thaliana. This protocol describes the method to isolate the MTL complex and to study the implication of a component of this complex (AtMic60) in mitochondria lipid trafficking.
Assuntos
Lipoproteínas/metabolismo , Proteínas de Membrana/metabolismo , Mitocôndrias/metabolismo , Membranas Mitocondriais/metabolismo , Complexos Multiproteicos/metabolismo , Transporte Biológico , Cromatografia Líquida , Lipoproteínas/isolamento & purificação , Espectrometria de Massas , Proteínas de Membrana/isolamento & purificação , SolubilidadeRESUMO
Plastids are organelles delineated by two envelopes that play important roles in different cellular processes such as energy production or lipid biosynthesis. To regulate their biogenesis and their function, plastids have to communicate with other cellular compartments. This communication can be mediated by signaling molecules and by the establishment of direct contacts between the plastid envelope and other organelles such as the endoplasmic reticulum, the mitochondria, the plasma membrane, the peroxisomes and the nucleus. These interactions are highly dynamic and respond to different biotic and abiotic stresses. However, the mechanisms involved in the formation of plastid-organelle contact sites and their functions are still enigmatic. In this chapter, we summarize our current knowledge about plastid contact sites and their role in the regulation of plastid biogenesis and function.
Assuntos
Plastídeos/fisiologia , Transdução de Sinais , Transporte Biológico , Membrana Celular/metabolismo , Núcleo Celular/metabolismo , Retículo Endoplasmático/fisiologia , Metabolismo Energético , Mitocôndrias/genética , Mitocôndrias/metabolismo , Peroxissomos/genética , Peroxissomos/metabolismo , Estresse FisiológicoRESUMO
Plastids are organelles playing fundamental roles in different cellular processes such as energy metabolism or lipid biosynthesis. To fulfill their biogenesis and their function in the cell, plastids have to communicate with other cellular compartments. This communication can be mediated by the establishment of direct contact sites between plastids envelop and other organelles. These contacts are dynamic structures that are modified in response to stress. As example, during phosphate (Pi) starvation, the number of contact sites between plastids and mitochondria significantly increases. In this situation, these contacts play an important role in the transfer of galactoglycerolipids from plastids to mitochondria. Recently, Pi starvation stress was used to identify key proteins involved in the traffic of galactoglycerolipids from plastids to mitochondria in Arabidopsis thaliana. A mitochondrial lipoprotein complex called MTL (mitochondrial transmembrane lipoprotein complex) was identified. This complex contains mitochondrial proteins but also proteins located in the plastid envelope, suggesting its presence at the plastid-mitochondria junction. This chapter describes the protocol to isolate the MTL complex by clear-native polyacrylamide gel electrophoresis (CN-PAGE) from the mitochondrial fraction of Arabidopsis cell cultures and the methods to study different features of this complex.
Assuntos
Mitocôndrias/metabolismo , Proteínas Mitocondriais/metabolismo , Complexos Multiproteicos/metabolismo , Plastídeos/metabolismo , Arabidopsis , Fracionamento Celular/métodos , Membrana Celular/metabolismo , Células Cultivadas , Centrifugação com Gradiente de Concentração , Fluxo de TrabalhoRESUMO
Lipid trafficking between mitochondria and other organelles is required for mitochondrial membrane biogenesis and signaling. This lipid exchange occurs by poorly understood nonvesicular mechanisms. In yeast and mammalian cells, this lipid exchange is thought to take place at contact sites between mitochondria and the ER or vacuolar membranes. Some proteins involved in the tethering between membranes or in the transfer of lipids in mitochondria have been identified. However, in plants, little is known about the synthesis of mitochondrial membranes. Mitochondrial membrane biogenesis is particularly important and noteworthy in plants as the lipid composition of mitochondrial membranes is dramatically changed during phosphate starvation and other stresses. This review focuses on the principal pathways involved in the synthesis of the most abundant mitochondrial glycerolipids in plants and the lipid trafficking that is required for plant mitochondria membrane biogenesis.
Assuntos
Arabidopsis/metabolismo , Glicolipídeos/biossíntese , Mitocôndrias/metabolismo , Membranas Mitocondriais/metabolismo , Proteínas Mitocondriais/metabolismo , Arabidopsis/genética , Transporte Biológico , Retículo Endoplasmático/química , Retículo Endoplasmático/metabolismo , Expressão Gênica , Glicolipídeos/química , Metabolismo dos Lipídeos , Mitocôndrias/química , Membranas Mitocondriais/química , Proteínas Mitocondriais/genética , Biogênese de Organelas , Plastídeos/química , Plastídeos/metabolismo , Vacúolos/química , Vacúolos/metabolismoRESUMO
The mitochondrion is an organelle originating from an endosymbiotic event and playing a role in several fundamental processes such as energy production, metabolite syntheses, and programmed cell death. This organelle is delineated by two membranes whose synthesis requires an extensive exchange of phospholipids with other cellular organelles such as endoplasmic reticulum (ER) and vacuolar membranes in yeast. These transfers of phospholipids are thought to occur by a non-vesicular pathway at contact sites between two closely apposed membranes. In plants, little is known about the biogenesis of mitochondrial membranes. Contact sites between ER and mitochondria are suspected to play a similar role in phospholipid trafficking as in yeast, but this has never been demonstrated. In contrast, it has been shown that plastids are able to transfer lipids to mitochondria during phosphate starvation. However, the proteins involved in such transfer are still unknown. Here, we identified in Arabidopsis thaliana a large lipid-enriched complex called the mitochondrial transmembrane lipoprotein (MTL) complex. The MTL complex contains proteins located in the two mitochondrial membranes and conserved in all eukaryotic cells, such as the TOM complex and AtMic60, a component of the MICOS complex. We demonstrate that AtMic60 contributes to the export of phosphatidylethanolamine from mitochondria and the import of galactoglycerolipids from plastids during phosphate starvation. Furthermore, AtMic60 promotes lipid desorption from membranes, likely as an initial step for lipid transfer, and binds to Tom40, suggesting that AtMic60 could regulate the tethering between the inner and outer membranes of mitochondria.
Assuntos
Proteínas de Arabidopsis/genética , Arabidopsis/metabolismo , Metabolismo dos Lipídeos , Mitocôndrias/metabolismo , Proteínas de Transporte da Membrana Mitocondrial/genética , Transporte Proteico , Proteínas de Arabidopsis/metabolismo , Proteínas de Transporte da Membrana Mitocondrial/metabolismoRESUMO
The biogenesis of photosynthetic membranes relies on galactoglycerolipids, which are synthesized via pathways that are dispatched over several cell compartments. This membrane biogenesis requires both trafficking of lipid intermediates and a tight homeostatic regulation. In this work, we address the role of ALA10 (for aminophospholipid ATPase), a P4-type ATPase, in a process counteracting the monogalactosyldiacylglycerol (MGDG) shortage in Arabidopsis (Arabidopsis thaliana) leaves. ALA10 can interact with protein partners, ALIS1 (for ALA-interacting subunit1) or ALIS5, leading to differential endomembrane localizations of the interacting proteins, close to the plasma membrane with ALIS1 or to chloroplasts with ALIS5. ALA10 interacts also with FATTY ACID DESATURASE2 (FAD2), and modification of ALA10 expression affects phosphatidylcholine (PC) fatty acyl desaturation by disturbing the balance between FAD2 and FAD3 activities. Modulation of ALA10 expression downstream impacts the fatty acyl composition of chloroplast PC. ALA10 expression also enhances leaf growth and improves the MGDG-PC ratio, possibly through MGDG SYNTHASE1 (MGD1) activation by phosphatidic acid. The positive effect of ALA10 on leaf development is significant in conditions such as upon treatment of plants with Galvestine-1, an inhibitor of MGDG synthases, or when plants are grown at chilling temperature.
Assuntos
Adenosina Trifosfatases/metabolismo , Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Ácidos Graxos Dessaturases/metabolismo , Fosfatidilcolinas/metabolismo , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Cloroplastos/metabolismo , Retículo Endoplasmático/metabolismo , Galactolipídeos/metabolismo , Perfilação da Expressão Gênica , Metabolismo dos Lipídeos , Folhas de Planta/metabolismo , Plantas Geneticamente ModificadasRESUMO
In higher plants, fatty acids (FAs) with 18 carbons (18C) represent about 70% of total FAs, the most abundant species being 18:2 and 18:3. These two polyunsaturated FAs (PUFAs) represent about 55% of total FAs in Arabidopsis cell suspension cultures, whereas 18:1 represents about 10%. The level of PUFAs may vary, depending on ill-defined factors. Here, we compared various sets of plant cell cultures and noticed a correlation between the growth rate of a cell population and the level of unsaturation of 18C FAs. These observations suggest that the final level of PUFAs might depend in part on the rate of cell division, and that FAD2 and FAD3 desaturases, which are respectively responsible for the formation of 18:2 and 18:3 on phospholipids, have limiting activities in fast-growing cultures. In plant cell culture, phosphate (Pi) deprivation is known to impair cell division and to trigger lipid remodeling. We observed that Pi starvation had no effect on the expression of FAD genes, and that the level of PUFAs in this situation was also correlated with the growth rate. Thus, the level of PUFAs appears as a hallmark in determining cell maturity and aging.
Assuntos
Arabidopsis/citologia , Ácidos Graxos Insaturados/farmacologia , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Divisão Celular/efeitos dos fármacos , Ácidos Graxos Dessaturases/genética , Ácidos Graxos Dessaturases/metabolismo , Fosfatos/deficiência , Fosfatos/metabolismo , Células Vegetais/efeitos dos fármacos , Células Vegetais/metabolismo , Reação em Cadeia da Polimerase em Tempo RealRESUMO
The understanding of chloroplast function requires the precise localization of proteins in each of its sub-compartments. High-sensitivity mass spectrometry has allowed the inventory of proteins in thylakoid, stroma, and envelope fractions. Concerning membrane association, proteins can be either integral or peripheral or even soluble proteins bound transiently to a membrane complex. We sought a method providing information at the surface of the outer envelope membrane (OEM), based on specific tagging with biotin or proteolysis using thermolysin, a non-membrane permeable protease. To evaluate this method, envelope, thylakoid, and stroma proteins were separated by two-dimensional electrophoresis and analyzed by immunostaining and mass spectrometry. A short selection of proteins associated to the chloroplast envelope fraction was checked after superficial treatments of intact chloroplasts. We showed that this method could allow the characterization of OEM embedded proteins facing the cytosol, as well as peripheral and soluble proteins associated via tight or lose interactions. Some stromal proteins were associated with biotinylated spots and analyzes are still needed to determine whether polypeptides were tagged prior import or if they co-migrated with OEM proteins. This method also suggests that some proteins associated with the inner envelope membrane (IEM) might need the integrity of a trans-envelope (IEM-OEM) protein complex (e.g., division ring-forming components) or at least an intact OEM partner. Following this evaluation, proteomic analyzes should be refined and the putative role of inter-membrane space components stabilizing trans-envelope complexes demonstrated. For future comprehensive studies, perspectives include the dynamic analyses of OEM proteins and IEM-OEM complexes in various physiological contexts and using virtually any other purified membrane organelle.
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Intracellular targeting of mRNAs has recently emerged as a prevalent mechanism to control protein localization. For mitochondria, a cotranslational model of protein import is now proposed in parallel to the conventional posttranslational model, and mitochondrial targeting of mRNAs has been demonstrated in various organisms. Voltage-dependent anion channels (VDACs) are the most abundant proteins in the outer mitochondrial membrane and the major transport pathway for numerous metabolites. Four nucleus-encoded VDACs have been identified in Arabidopsis thaliana. Alternative cleavage and polyadenylation generate two VDAC3 mRNA isoforms differing by their 3' UTR. By using quantitative RT-PCR and in vivo mRNA visualization approaches, the two mRNA variants were shown differentially associated with mitochondria. The longest mRNA presents a 3' extension named alternative UTR (aUTR) that is necessary and sufficient to target VDAC3 mRNA to the mitochondrial surface. Moreover, aUTR is sufficient for the mitochondrial targeting of a reporter transcript, and can be used as a tool to target an unrelated mRNA to the mitochondrial surface. Finally, VDAC3-aUTR mRNA variant impacts mitochondria morphology and size, demonstrating the role of mRNA targeting in mitochondria biogenesis.
Assuntos
Proteínas de Arabidopsis/genética , Mitocôndrias/metabolismo , Proteínas de Transporte da Membrana Mitocondrial/genética , Isoformas de RNA , Canais de Ânion Dependentes de Voltagem/genética , Regiões 3' não Traduzidas , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Núcleo Celular/metabolismo , Genes de Plantas , Proteínas de Transporte da Membrana Mitocondrial/metabolismo , Membranas Mitocondriais/metabolismo , Mutação , Fenótipo , Porinas/metabolismo , Transporte Proteico , RNA Mensageiro/metabolismo , Canais de Ânion Dependentes de Voltagem/metabolismoRESUMO
Glycerolipids constituting the matrix of photosynthetic membranes, from cyanobacteria to chloroplasts of eukaryotic cells, comprise monogalactosyldiacylglycerol, digalactosyldiacylglycerol, sulfoquinovosyldiacylglycerol and phosphatidylglycerol. This review covers our current knowledge on the structural and functional features of these lipids in various cellular models, from prokaryotes to eukaryotes. Their relative proportions in thylakoid membranes result from highly regulated and compartmentalized metabolic pathways, with a cooperation, in the case of eukaryotes, of non-plastidic compartments. This review also focuses on the role of each of these thylakoid glycerolipids in stabilizing protein complexes of the photosynthetic machinery, which might be one of the reasons for their fascinating conservation in the course of evolution. This article is part of a Special Issue entitled: Dynamic and ultrastructure of bioenergetic membranes and their components.
Assuntos
Glicolipídeos/biossíntese , Lipídeos de Membrana/biossíntese , Fotossíntese , Tilacoides/metabolismo , Transporte Biológico , Vias Biossintéticas , Células Eucarióticas/química , Células Eucarióticas/metabolismo , Glicolipídeos/química , Glicolipídeos/metabolismo , Lipídeos de Membrana/química , Lipídeos de Membrana/metabolismo , Células Procarióticas/química , Células Procarióticas/metabolismo , Estabilidade Proteica , Tilacoides/químicaRESUMO
Mitochondria contain hundreds of proteins but only a few are encoded by the mitochondrial genome. The other proteins are nuclear-encoded and imported into mitochondria. These proteins can be translated on free cytosolic polysomes, then targeted and imported into mitochondria. Nonetheless, numerous cytosolic mRNAs encoding mitochondrial proteins are detected at the surface of mitochondria in yeast, plants and animals. The localization of mRNAs to the vicinity of mitochondria would be a way for mitochondrial protein sorting. The mechanisms responsible for mRNA targeting to mitochondria are not clearly identified. Sequences within the mRNA molecules (cis-elements), as well as a few trans-acting factors, have been shown to be essential for targeting of some mRNAs. In order to identify receptors involved in mRNA docking to the mitochondrial surface, we have developed an in vitro mRNA binding assay with isolated plant mitochondria. We show that naked mRNAs are able to bind to isolated mitochondria, and our results strongly suggest that mRNA docking to the plant mitochondrial outer membrane requires at least one component of TOM complex.