ABSTRACT
The cell wall (CW) and plasma membrane are fundamental structures that define cell shape and support different cellular functions. In pathogenic fungi, such as Aspegillus fumigatus, they not only play structural roles but are also important for virulence and immune recognition. Both the CW and the plasma membrane remain as attractive drug targets to treat fungal infections, such as the Invasive Pulmonary Aspergillosis (IPA), a disease associated with high morbimortality in immunocompromised individuals. The low efficiency of echinocandins that target the fungal CW biosynthesis, the occurrence of environmental isolates resistant to azoles such as voriconazole and the known drawbacks associated with amphotericin toxicity foster the urgent need for fungal-specific drugable targets and/or more efficient combinatorial therapeutic strategies. Reverse genetic approaches in fungi unveil that perturbations of the CW also render cells with increased susceptibility to membrane disrupting agents and vice-versa. However, how the fungal cells simultaneously cope with perturbation in CW polysaccharides and cell membrane proteins to allow morphogenesis is scarcely known. Here, we focus on current information on how the main signaling pathways that maintain fungal cell wall integrity, such as the Cell Wall Integrity and the High Osmolarity Glycerol pathways, in different species often cross-talk to regulate the synthesis of molecules that comprise the plasma membrane, especially sphingolipids, ergosterol and phospholipids to promote functioning of both structures concomitantly and thus, cell viability. We propose that the conclusions drawn from other organisms are the foundations to point out experimental lines that can be endeavored in A. fumigatus.
Subject(s)
Aspergillus fumigatus/drug effects , Aspergillus fumigatus/metabolism , Cell Wall/metabolism , Membrane Lipids/biosynthesis , Antifungal Agents/pharmacology , Aspergillus fumigatus/cytology , Cell Survival/drug effects , Cell Wall/drug effects , Signal Transduction/drug effectsABSTRACT
The glycerophospholipids phosphatidylethanolamine, phosphatidylglycerol (PG), and cardiolipin (CL) are major structural components of bacterial membranes. In some bacteria, phosphatidylcholine or phosphatidylinositol and its derivatives form part of the membrane. PG or CL can be modified with the amino acid residues lysine, alanine, or arginine. Diacylglycerol is the lipid anchor from which syntheses of phosphorus-free glycerolipids, such as glycolipids, sulfolipids, or homoserine-derived lipids initiate. Many membrane lipids are subject to turnover and some of them are recycled. Other lipids associated with the membrane include isoprenoids and their derivatives such as hopanoids. Ornithine-containing lipids are widespread in Bacteria but absent in Archaea and Eukarya. Some lipids are probably associated exclusively with the outer membrane of many bacteria, i.e. lipopolysaccharides, sphingolipids, or sulfonolipids. For certain specialized membrane functions, specific lipid structures might be required. Upon cyst formation in Azotobacter vinelandii, phenolic lipids are accumulated in the membrane. Anammox bacteria contain ladderane lipids in the membrane surrounding the anammoxosome organelle, presumably to impede the passage of highly toxic compounds generated during the anammox reaction. Considering that present knowledge on bacterial lipids was obtained from only a few bacterial species, we are probably only starting to unravel the full scale of lipid diversity in bacteria. This article is part of a Special Issue entitled: Bacterial Lipids edited by Russell E. Bishop.
Subject(s)
Bacteria/metabolism , Diglycerides/biosynthesis , Glycerophospholipids/biosynthesis , Lipogenesis , Membrane Lipids/biosynthesis , Diglycerides/chemistry , Diglycerides/classification , Glycerophospholipids/chemistry , Glycerophospholipids/classification , Membrane Lipids/chemistry , Membrane Lipids/classification , Molecular Structure , Structure-Activity RelationshipABSTRACT
In the bacterial model organism Escherichia coli only the three major membrane lipids phosphatidylethanolamine, phosphatidylglycerol, and cardiolipin occur, all of which belong to the glycerophospholipids. The amino acid-containing phosphatidylserine is a major lipid in eukaryotic membranes but in most bacteria it occurs only as a minor biosynthetic intermediate. In some bacteria, the anionic glycerophospholipids phosphatidylglycerol and cardiolipin can be decorated with aminoacyl residues. For example, phosphatidylglycerol can be decorated with lysine, alanine, or arginine whereas in the case of cardiolipin, lysine or d-alanine modifications are known. In few bacteria, diacylglycerol-derived lipids can be substituted with lysine or homoserine. Acyl-oxyacyl lipids in which the lipidic part is amide-linked to the alpha-amino group of an amino acid are widely distributed among bacteria and ornithine-containing lipids are the most common version of this lipid type. Only few bacterial groups form glycine-containing lipids, serineglycine-containing lipids, sphingolipids, or sulfonolipids. Although many of these amino acid-containing bacterial membrane lipids are produced in response to certain stress conditions, little is known about the specific molecular functions of these lipids.
Subject(s)
Amino Acids/metabolism , Bacteria/metabolism , Membrane Lipids/metabolism , Bacteria/enzymology , Cardiolipins/biosynthesis , Cardiolipins/metabolism , Diglycerides/biosynthesis , Diglycerides/metabolism , Glycerophospholipids/biosynthesis , Glycerophospholipids/metabolism , Membrane Lipids/biosynthesis , Membrane Lipids/chemistry , Phosphatidylglycerols/biosynthesis , Phosphatidylglycerols/metabolism , Serine C-Palmitoyltransferase/classification , Serine C-Palmitoyltransferase/metabolism , Sphingolipids/biosynthesis , Sphingolipids/metabolismABSTRACT
Bacterial cells stringently regulate the synthesis of their membrane phospholipids but the responsible mechanisms are incompletely understood. Recent biochemical, genetic and structural analyses have greatly expanded the knowledge of lipid metabolism in Gram-positive bacteria, revealing that these organisms use novel mechanisms to regulate this essential pathway. A remarkable progress was the identification of a new pathway for the initiation of phospholipid biosynthesis that uncovered a mechanism that coordinates fatty acid and phospholipid biosynthesis. Recent advances in structure determination of a global transcription factor have led to significant insights of the underlying complexities and functional elegance of membrane lipid homeostasis in Gram-positive bacteria.
Subject(s)
Fatty Acid Synthase, Type II/metabolism , Gene Expression Regulation, Bacterial , Gram-Positive Bacteria/enzymology , Membrane Lipids/biosynthesis , Fatty Acid Synthase, Type II/genetics , Gram-Positive Bacteria/genetics , Membrane Lipids/chemistry , Models, Molecular , Phospholipids/biosynthesis , Transcription Factors/chemistry , Transcription Factors/genetics , Transcription Factors/metabolism , Transcription, GeneticABSTRACT
Fatty acid synthesis is coordinately regulated with phospholipid, macromolecular synthesis and growth as part of the response to changes in the environment. Many of these processes are rapid responses of the integrated biochemical network and do not involve changes in gene expression. An important recent development is the identification and characterization of transcription factors that modify pathway activity by either altering the expression levels of a few important genes or controlling a global adjustment in the expression of the entire pathway. For most of these transcription factors the signaling molecules controlling their activities are still poorly defined.
Subject(s)
Bacteria/genetics , Gene Expression Regulation, Bacterial , Membrane Lipids/biosynthesis , Transcription, Genetic , Bacteria/metabolismABSTRACT
Phosphatidylcholine (PC) is the major membrane-forming phospholipid in eukaryotes with important structural and signalling functions. Although many prokaryotes lack PC, it can be found in significant amounts in membranes of rather diverse bacteria. Two pathways for PC biosynthesis are known in bacteria, the methylation pathway and the phosphatidylcholine synthase (PCS) pathway. In the methylation pathway, phosphatidylethanolamine is methylated three times to yield PC, in reactions catalysed by one or several phospholipid N-methyltransferases (PMTs). In the PCS pathway, choline is condensed directly with CDP-diacylglyceride to form PC in a reaction catalysed by PCS. Using cell-free extracts, it was demonstrated that Sinorhizobium meliloti, Agrobacterium tumefaciens, Rhizobium leguminosarum, Bradyrhizobium japonicum, Mesorhizobium loti and Legionella pneumophila have both PMT and PCS activities. In addition, Rhodobacter sphaeroides has PMT activity and Brucella melitensis, Pseudomonas aeruginosa and Borrelia burgdorferi have PCS activities. Genes from M. loti and L. pneumophila encoding a Pmt or a Pcs activity and the genes from P. aeruginosa and Borrelia burgdorferi responsible for Pcs activity have been identified. Based on these functional assignments and on genomic data, one might predict that if bacteria contain PC as a membrane lipid, they usually possess both bacterial pathways for PC biosynthesis. However, important pathogens such as Brucella melitensis, P. aeruginosa and Borrelia burgdorferi seem to be exceptional as they possess only the PCS pathway for PC formation.
Subject(s)
Bacteria/metabolism , Phosphatidylcholines/biosynthesis , Bacteria/genetics , Base Sequence , CDPdiacylglycerol-Serine O-Phosphatidyltransferase/genetics , CDPdiacylglycerol-Serine O-Phosphatidyltransferase/metabolism , DNA, Bacterial/genetics , Diacylglycerol Cholinephosphotransferase/genetics , Diacylglycerol Cholinephosphotransferase/metabolism , Genes, Bacterial , Membrane Lipids/biosynthesis , Methylation , Methyltransferases/genetics , Methyltransferases/metabolism , Open Reading Frames , Phosphatidyl-N-Methylethanolamine N-Methyltransferase , PhylogenyABSTRACT
Bacterial cells exert exquisite control over the biosynthesis of their membrane lipids, but the mechanisms are obscure. We describe the identification and purification from Bacillus subtilis of a transcription factor, FapR, that controls the expression of many genes involved in fatty acid and phospholipid metabolism (the fap regulon). Expression of this fap regulon is influenced by antibiotics that specifically inhibit the fatty acid biosynthetic pathway. We show that FapR negatively regulates fap expression and that the effects of antibiotics on fap expression are mediated by FapR. We further show that decreasing the cellular levels of malonyl-CoA, an essential molecule for fatty acid elongation, inhibits expression of the fap regulon and that this effect is FapR dependent. Our results indicate that control of FapR by the cellular pools of malonyl-CoA provides a mechanism for sensing the status of fatty acid biosynthesis and to adjust the expression of the fap regulon accordingly.
Subject(s)
Bacillus subtilis , Escherichia coli Proteins/genetics , Escherichia coli Proteins/metabolism , Membrane Lipids/biosynthesis , Transcription Factors/genetics , Transcription Factors/metabolism , Amino Acid Sequence , Bacillus subtilis/genetics , Bacillus subtilis/metabolism , Base Sequence , Cell Division , Conserved Sequence/genetics , DNA-Binding Proteins/chemistry , DNA-Binding Proteins/genetics , DNA-Binding Proteins/isolation & purification , DNA-Binding Proteins/metabolism , Escherichia coli Proteins/chemistry , Escherichia coli Proteins/isolation & purification , Fatty Acids/biosynthesis , Fatty Acids/chemistry , Gene Deletion , Gene Expression Regulation, Bacterial , Malonyl Coenzyme A/metabolism , Membrane Lipids/chemistry , Molecular Sequence Data , Promoter Regions, Genetic/genetics , Sequence Homology, Amino Acid , Time Factors , Transcription Factors/chemistry , Transcription Factors/isolation & purification , Transcription, GeneticABSTRACT
The synthesis of phosphatidylcholine (PC) in rod outer segments (ROS) catalysed by lysophosphatidylcholine acyltransferase and phosphatidylethanolamine N-methyltransferase (PE N-MTase) was studied and the effects of natural (FA and lysophospholipids) and synthetic (Triton X-100, deoxycholate and CHAPS) surfactants was evaluated. In all experimental conditions used, incorporation of labelled oleate into lysophosphatidylcholine (lysoPC) was at least 40 times greater than oleate incorporation into any other lysophospholipid. Acylation of lysoPC was slightly affected by Triton X-100 and was totally inhibited in the presence of 10 mM sodium deoxycholate (NaDOC) or CHAPS. Below their critical micelle concentration (cmc) Triton X-100 and NaDOC stimulated acylation of all ROS lysophospholipids analysed. The activity of PE N-MTase was stimulated at detergent concentrations below the cmc and inhibited at concentrations above the cmc for all three detergents tested. The effect of FA with differing degree of unsaturation on PC synthesis was evaluated. Oleic acid (10 microM) inhibited methyl group incorporation into total PC, whereas from 100 microM onward, the methylating activity increased with preferential synthesis of PC. Docosahexaenoic acid, in turn, inhibited PE N-MTase activity at every concentration tested. These results suggest that PC synthesis in ROS membranes is modified by bioregulators and surfactants altering the physico-chemical state of the membrane.
Subject(s)
Detergents/pharmacology , Intracellular Membranes/drug effects , Membrane Lipids/biosynthesis , Phosphatidylcholines/biosynthesis , Rod Cell Outer Segment/drug effects , Surface-Active Agents/pharmacology , 1-Acylglycerophosphocholine O-Acyltransferase/metabolism , Acylation , Animals , Cattle , Cholic Acids/pharmacology , Deoxycholic Acid/pharmacology , Docosahexaenoic Acids/pharmacology , Fatty Acids/pharmacology , Intracellular Membranes/metabolism , Lysophospholipids/pharmacology , Membrane Proteins/metabolism , Methyltransferases/metabolism , Octoxynol/pharmacology , Oleic Acid/metabolism , Oleic Acid/pharmacology , Phosphatidylethanolamine N-Methyltransferase , Rod Cell Outer Segment/metabolism , Stimulation, ChemicalABSTRACT
The last step in the synthesis of lignin and suberin has been proposed to be catalyzed by peroxidases, although other proteins may also be involved. To determine which peroxidases are involved in the synthesis of lignin and suberin, five peroxidases from tomato (Lycopersicon esculentum) roots, representing the majority of the peroxidase activity in this organ, have been partially purified and characterized kinetically. The purified peroxidases with isoelectric point (pI) values of 3.6 and 9.6 showed the highest catalytic efficiency when the substrate used was syringaldazine, an analog of lignin monomer. Using a combination of transgenic expression and antibody recognition, we now show that the peroxidase pI 9.6 is probably encoded by TPX1, a tomato peroxidase gene we have previously isolated. In situ RNA hybridization revealed that TPX1 expression is restricted to cells undergoing synthesis of lignin and suberin. Salt stress has been reported to induce the synthesis of lignin and/or suberin. This stress applied to tomato caused changes in the expression pattern of TPX1 and induced the TPX1 protein. We propose that the TPX1 product is involved in the synthesis of lignin and suberin.
Subject(s)
Lignin/biosynthesis , Membrane Lipids/biosynthesis , Peroxidases/metabolism , Solanum lycopersicum/enzymology , Kinetics , Lipids , Peroxidases/geneticsABSTRACT
Phosphatidylinositol (PtdIns) synthesis and polyphosphoinositide (PPI) formation were measured as the incorporation of [32P]orthophosphate ([32P]Pi) or [3H]inositol into non-stimulated intact human neutrophil membrane phospholipids. The rate of PtdIns "de novo" synthesis appeared to be a slow mechanism when compared to the rapid incorporation of [32P]Pi into PPIs. Of the "de novo" synthesized [3H]PtdIns, 70% was further phosphorylated to PPI. Nevertheless, this PPI pool represented less than 0.01% of the total nmols of PPIs formed evaluated as [32P]Pi labeling, indicating that PPI formation mainly involves a no "de novo" synthesized phosphatidylinositol pool. When evaluated at short incubation times, oscillations in the formation of PPIs were detected. A rapid phase was characterized after 30 s of incubation with [32P]Pi Phosphorylation levels returned to an equilibrium state within a minute, and the second phase peaked at 5 min., returning to equilibrium at 15 min. The fluctuant kinetics though not the equilibrium level of PPI formation, could be abolished by neomycin. On the other hand, a selective inhibition of the rapid phase of PPI synthesis occurred in the presence of the tyrosine kinase inhibitor genistein. When the incorporations of [gamma-32P]-adenosine triphosphate (ATP) or [32P]Pi into human neutrophil particulate fraction membranes were evaluated, PPIs synthesis showed fluctuations independently of the precursor used. Noticeably, [32P]from [32P]Pi was incorporated more efficiently into PPIs than that from [gamma-32P]ATP, when evaluated in parallel using equal specific activities for both radiolabeled precursors and under non-ATP synthesizing conditions. Moreover, the incorporation of [32P]Pi into particulate fraction PPIs was not abolished by high concentrations of non-radiolabeled ATP, and metabolically inhibited PMNs showed high rates of PPI synthesis. These data suggest that PPI formation is not necessarily a futile cycle in PMNs.
Subject(s)
Membrane Lipids/biosynthesis , Neutrophils/metabolism , Phosphatidylinositol Phosphates/biosynthesis , Adenosine Triphosphate/metabolism , Adult , Antimetabolites/pharmacology , Deoxyglucose/pharmacology , Diphosphates/metabolism , Energy Metabolism/drug effects , Genistein/pharmacology , Humans , Kinetics , Magnesium/pharmacology , Neomycin/pharmacology , Neutrophils/drug effects , Oligomycins/pharmacology , Phosphatidylinositols/biosynthesis , Phosphorylation , Protein-Tyrosine Kinases/antagonists & inhibitorsABSTRACT
Lipid bodies, inducible lipid-rich cytoplasmic inclusions, are characteristically abundant in cells associated with inflammation, including eosinophils. Here we reviewed the formation and function of lipid bodies in human eosinophils. We now have evidence that the formation of lipid bodies is not attributable to adverse mechanisms, but is centrally mediated by specific signal transduction pathways. Arachidonic acid and other cis fatty acids by an NSAID-inhibitable process, diglycerides, and PAF by a 5-lipoxygenase dependent pathway are potent stimulators of lipid body induction. Lipid body formation develops rapidly by processes that involve PKC, PLC, and de novo mRNA and protein synthesis. These structures clearly serve as repositories of arachidonyl-phospholipids and are more than inert depots. Specific enzymes, including cytosolic phospholipase A2, MAP kinases, lipoxygenases and cyclooxygenases, associate with lipid bodies. Lipid bodies appear to be dynamic, organelle-like structures involved in intracellular pathways of lipid mobilization and metabolism. Indeed, increases in lipid body numbers correlated with enhanced production of both lipoxygenase- and cyclooxygenase-derived eicosanoids. We hypothesize that lipid bodies are distinct inducible sites for generating eicosanoids as paracrine mediators with varied activities in inflammation. The capacity of lipid body formation to be specifically and rapidly induced in leukocytes enhances eicosanoid mediator formation, and conversely pharmacologic inhibition of lipid body induction represents a potential novel and specific target for anti-inflammatory therapy.
Subject(s)
Arachidonic Acid/metabolism , Eicosanoids/biosynthesis , Eosinophils/physiology , Membrane Lipids/physiology , Signal Transduction/physiology , Arachidonic Acid/therapeutic use , Humans , Hypereosinophilic Syndrome , Inflammation , Inflammation Mediators/physiology , Membrane Lipids/antagonists & inhibitors , Membrane Lipids/biosynthesis , Signal Transduction/immunologyABSTRACT
The developmental profiles of the lipid composition and their de novo synthesis and remodelling in the optic lobe of the chicken were studied. The 32P incorporation to phospholipids showed an active de novo synthesis mainly of phosphatidylinositol and of a particular fraction of phosphatidylcholine during the early stages of the embryo development, concomitantly with the beginning of synaptogenesis. This de novo synthesis of phospholipids strongly increased at hatching. On the other hand, phosphatidylinositol presented an active lipid exchange (acylation-deacylation) in the early stages of embryogenesis, indicating a strong incorporation of 14C-arachidonic acid during this period, followed by a fast drop in specific activity. Two different fractions of phosphatidylcholine were isolated by high-performance thin-layer chromatography with a different profile of fatty acid composition, disclosing their different physicochemical behavior, metabolic activities and evolution during embryogenesis. 32P incorporation into phosphatidylethanolamine remained very low during the earliest stages of embryogenesis, showing an increase when the process of synaptogenesis began, until hatching, when radioactivity reached a plateau. 14C-arachidonic acid incorporation into phosphatidylethanolamine was minimal. Furthermore, the phosphatidylethanolamine pool was progressively enriched in its ethanolamine plasmalogen throughout the development. Chromatographic analysis of lipid extracts showed the presence of cerebroside traces after 16 days of embryo incubation. At hatching, a remarkable increase in non-hydroxylated cerebrosides was observed concurrently with the appearance of hydroxylated ones. These glycosphingolipids, as well as the sulfatides, were markedly increased in the lipid extracts of optic lobes of adult animals, indicating the progressive development and maturity of the myelin sheath.