Fatty Acid Composition Of Membrane Lipids Research Articles

Genome-scale model of metabolism and gene expression provides a multi-scale description of acid stress responses in Escherichia coli.

Response to acid stress is critical for Escherichia coli to successfully complete its life-cycle by passing through the stomach to colonize the digestive tract. To develop a fundamental understanding of this response, we established a molecular mechanistic description of acid stress mitigation responses in E. coli and integrated them with a genome-scale model of its metabolism and macromolecular expression (ME-model). We considered three known mechanisms of acid stress mitigation: 1) change in membrane lipid fatty acid composition, 2) change in periplasmic protein stability over external pH and periplasmic chaperone protection mechanisms, and 3) change in the activities of membrane proteins. After integrating these mechanisms into an established ME-model, we could simulate their responses in the context of other cellular processes. We validated these simulations using RNA sequencing data obtained from five E. coli strains grown under external pH ranging from 5.5 to 7.0. We found: i) that for the differentially expressed genes accounted for in the ME-model, 80% of the upregulated genes were correctly predicted by the ME-model, and ii) that these genes are mainly involved in translation processes (45% of genes), membrane proteins and related processes (18% of genes), amino acid metabolism (12% of genes), and cofactor and prosthetic group biosynthesis (8% of genes). We also demonstrated several intervention strategies on acid tolerance that can be simulated by the ME-model. We thus established a quantitative framework that describes, on a genome-scale, the acid stress mitigation response of E. coli that has both scientific and practical uses.

The effect of benzylaminopurine on fatty-acid composition of membrane lipids in shoots of Karelian birch in vitro

The effect of the synthetic analogue of natural cytokinin 6-benzylaminopurine (BAP) on the fatty-acid composition of membrane lipids in shoots of Karelian (Curly) birch Betula pendula Roth var. carelica (Mercklin) Hamet-Ahti under in vitro conditions was studied. It was found that the addition of BAP (in a concentration of 0.25, 0.5, 1.0, or 2 mg/L) to the nutrient medium leads to an increase in the proportion of saturated fatty acids in phospholipids, whereas in the control variant unsaturated fatty acids predominated in phospholipids. In glycolipids, on the contrary, BAP caused an increase in the synthesis of unsaturated fatty acids (predominantly, linolenic), but the degree of its effect depended on the concentration of the hormone. In particular, when the maximum amount of the studied concentration (2.0 mg/L) was used, the use of BAP was shown to decrease the proportion of linolenic acid. It is suggested that the revealed changes in the composition of glycolipids are indicators of the stimulating effect of cytokinin (up to a certain concentration) on the structure and function of chloroplasts. Due to the photomixotrophy of shoot cultures, chloroplasts are an important factor determining not only their photosynthetic activity, but also cell proliferation and the direction of in vitro morphogenesis.

Analysis of effects of a new environmental pollutant, bisphenol A, on antioxidant systems in soybean roots at different growth stages.

Bisphenol A (BPA) is an important industrial raw material. Because of its widespread use and increasing release into environment, BPA has become a new environmental pollutant. Previous studies about BPA’s effects in plants focus on a certain growth stage. However, the plant’s response to pollutants varies at different growth stages. Therefore, in this work, BPA’s effects in soybean roots at different growth stages were investigated by determining the reactive oxygen species levels, membrane lipid fatty acid composition, membrane lipid peroxidation, and antioxidant systems. The results showed that low-dose BPA exposure slightly caused membrane lipid peroxidation but didn’t activate antioxidant systems at the seedling stage, and this exposure did not affect above process at other growth stages; high-dose BPA increased reactive oxygen species levels and then caused membrane lipid peroxidation at all growth stages although it activated antioxidant systems, and these effects were weaker with prolonging the growth stages. The recovery degree after withdrawal of BPA exposure was negatively related to BPA dose, but was positively related to growth stage. Taken together, the effects of BPA on antioxidant systems in soybean roots were associated with BPA exposure dose and soybean growth stage.

Reduced placental docosahexaenoic acid levels associated with increased levels of sFlt-1 in preeclampsia

Our earlier studies, in preeclamptic women have shown altered levels of long chain polyunsaturated fatty acids (LCPUFA), essential constituents of the cell membrane lipids responsible for membrane stability as one of the key factors contributing to the pathophysiology of preeclampsia. We have also reported elevated levels of sFlt-1 in preeclampsia. The present study examines the levels of LCPUFA and their association with sFlt-1 levels in 69 pre-eclamptic women and 40 normotensive women. DHA and omega 3 fatty acid levels were lower ( p<0.001) while arachidonic acid and omega 6 fatty acid levels were higher ( p<0.05) in preeclamptic women as compared to normotensive women. Maternal plasma sFlt-1 levels were higher ( p<0.05) in preeclamptic women and were negatively associated with DHA ( p=0.008) and omega 3 fatty acids concentrations ( p=0.031). Our results suggest that altered placental LCPUFA may result in altered membrane lipid fatty acid composition leading to increased release of sFlt-1 in circulation.

Substrate Preferences of a Lysophosphatidylcholine Acyltransferase Highlight Its Role in Phospholipid Remodeling

An important enzyme involved in phospholipid turnover is the acyl-CoA: lysophosphatidylcholine acyltransferase (LPCAT). Here, we report characterization of a newly discovered human LPCAT (LPCAT3), which has distinct substrate preferences strikingly consistent with a role in phosphatidylcholine (PtdCho) remodeling and modulating fatty acid composition of PtdCho. LPCAT3 prefers lysophosphatidylcholine (lysoPtdCho) with saturated fatty acid at the sn-1 position and exhibits acyl donor preference towards linoleoyl-CoA and arachidonoyl-CoA. Furthermore, LPCAT3 is active in mediating 1-O-alkyl-sn-glycero-3-phosphocholine acylation with long chain fatty acyl-CoAs to generate 1-O-alkyl-phosphatidylcholine, another very important constitute of mammalian membrane systems. These properties are precisely the known attributes of LPCAT previously ascribed to the isoform involved in Lands' cycle, and thus strongly suggest that LPCAT3 is involved in phospholipids remodeling to achieve appropriate membrane lipid fatty acid composition.

CO2- and anaerobiosis-induced changes in physiology and gene expression of different Listeria monocytogenes strains.

Although carbon dioxide (CO(2)) is known to inhibit growth of most bacteria, very little is known about the cellular response. The food-borne pathogen Listeria monocytogenes is characterized by its ability to grow in high CO(2) concentrations at refrigeration temperatures. We examined the listerial responses of different strains to growth in air, 100% N(2), and 100% CO(2). The CO(2)-induced changes in membrane lipid fatty acid composition and expression of selected genes were strain dependent. The acid-tolerant L. monocytogenes LO28 responded in the same manner to CO(2) as to other anaerobic, slightly acidic environments (100% N(2), pH 5.7). An increase in the expression of the genes encoding glutamate decarboxylase (essential for survival in strong acid) as well as an increased amount of branched-chain fatty acids in the membrane was observed in both atmospheres. In contrast, the acid-sensitive L. monocytogenes strain EGD responded differently to CO(2) and N(2) at the same pH. In a separate experiment with L. monocytogenes 412, an increased isocitrate dehydrogenase activity level was observed for cells grown in CO(2)-containing atmospheres. Together, our findings demonstrate that the CO(2)-response is a partly strain-dependent complex mechanism. The possible links between the CO(2)-dependent changes in isocitrate dehydrogenase activity, glutamate metabolism and branched fatty acid biosynthesis are discussed.

Changes in membrane lipid and free fatty acid composition during low temperature preconditioning against SO 2 injury in coleus

The effects of a low temperature (13 °C) treatment known to provide protection against sulphur dioxide (SO 2) injury were assessed on leaf lipid composition in two cultivars of Coleus blumei Benth, found previously to differ in sensitivity to SO 2 and other environmental stresses. After 5 days growth at 13 °C, there were significant differences in membrane lipid fatty acid composition as well as in free fatty acid (FFA) levels between SO 2-sensitive ‘Buckley Supreme’ (‘BS’) and SO 2-insensitive ‘Marty’ (‘M’). Molecular species of chloroplast galactolipids in ‘M’ contained increased levels of linolenic acid (18:3). In the leaf FFA pools, the saturated components, palmitic (16:0) and stearic (18:0) acids, were predominant at 20 °C. After temperature hardening at 13 °C, the total amount of FFAs decreased in ‘M’ but increased in ‘BS.’ These modifications in lipid composition suggest an additional mechanism for cultivar differences in tolerance to SO 2 and other stressors in coleus.

Expression of fatty acid binding proteins is altered in aged mouse brain.

Brain membrane lipid fatty acid composition and consequently membrane fluidity change with increasing age. Intracellular fatty acid binding proteins (FABPs) such as heart H-FABP and the brain specific B-FABP, detected by immunoblotting of brain tissue, are thought to be involved in fatty acid uptake, metabolism, and differentiation in brain. Yet, almost nothing is known regarding the effect of age on the expression of the cytosolic fatty acid binding proteins (FABPs) or their content in brain subfractions. Electrophoresis and quantitative immunoblotting were used to examine the content of these FABPs in synaptosomes in brains from 4, 15, and 25 month old C57BL/6NNia male mice. Brain H-FABP and B-FABP were differentially expressed in mouse brain subcellular fractions. Brain H-FABP was highly concentrated in synaptosomal cytosol. The level of brain H-FABP in synaptosomes, synaptosomal cytosol, and intrasynaptosomal membranes was decreased 33, 35, and 43%, respectively, in 25 month old mice. B-FABP was detected in lower quantity than H-FABP. More important, B-FABP decreased in synaptosomes, synaptic plasma membranes, and synaptosomal cytosol from brains of 25 month old mice. In contrast to H-FABP, B-FABP was not detectable in the intrasynaptosomal membranes in any of the three age groups of mice. In conclusion, expression of both H-FABP and B-FABP was markedly reduced in aged mouse brain. Age differences in brain H-FABP and B-FABP levels in synaptosomal plasma membranes and synaptosomal cytosol may be important factors modulating neuronal differentiation and function.

The fats of Escherichia coli during infancy and old age: regulation by global regulators, alarmones and lipid intermediates.

The fluidity and phase state of bacterial lipid bilayers commonly change in response to ambient environmental conditions to maintain the critical functions of the envelope as a semipermeable and selective boundary. A special, and intricate, set of alterations in membrane lipid metabolism is elicited by conditions causing growth arrest. Under such conditions, specific alterations in the membrane lipid-fatty acid composition are required for survival of the cell and, concurrently, the membrane lipids are suggested to serve as endogenous reserves providing carbon/energy for maintenance requirements. It appears that the global regulator FadR is required for both of these activities to be performed properly and that the FadR regulon is interconnected to the universal stress response of Escherichia coli. FadR, in conjunction with long-chain fatty acyl-CoA, long-chain acyl-ACP, ppGpp and cAMP, are key players in regulating the activities of enzymes and expression of genes involved in fatty acid and phospholipid metabolism in dividing and ageing E. coli cells.

Reevaluation of the pathways for the biosynthesis of polyunsaturated fatty acids.

Recent studies refute the commonly accepted, but untested, hypothesis that 7,10,13,16-22:4 and 7,10,13,16,19-22:5 are desaturated at position 4 by a microsomal acyl-CoA-dependent desaturase. The synthesis of 4,7,10,13,16,19-22:6 occurs via the following reaction sequence: 7,10,13,16,19-22:5-->9,12,15,18,21-24:5-->6,9,12,15,18,21-24:6 4,7,10,13,16,19-22:6. The synthesis of 4,7,10,13,16-22:5 from 7,10,13,16-22:4 takes place via an analogous pathway. According to these pathways the 24-carbon acids that are made in the endoplasmic reticulum move to a site for partial beta-oxidation, which is most likely peroxisomes. The products of partial beta-oxidation, 4,7,10,13,16-22:5 and 4,7,10,13,16,19-22:6, then move back to the endoplasmic reticulum where they are used as substrates for membrane lipid biosynthesis. The ability of a fatty acid to serve as a substrate for continued peroxisomal beta-oxidation, versus its transfer out of peroxisomes for subsequent endoplasmic reticulum-associated esterification reactions, may be an important control for regulating membrane lipid fatty acid composition. Indeed, the revised pathways of polyunsaturated fatty acid biosynthesis imply that there is considerable intracellular movement and recycling of fatty acids between peroxisomes and the endoplasmic reticulum. In addition, these revised pathways require that two 18-carbon and two 24-carbon acids are substrates for desaturation at position 6. Also, as linoleate and linolenate are metabolized, respectively, to 6,9,12,15,18-24:5 and 6,9,12,15,18,21-24:6, three n-6 acids and three n-3 acids are substrates for malonyl-CoA dependent chain elongation. It remains to be determined how many microsomal enzymes are required to carry out these reactions and whether other ancillary enzymes are expressed in tissues whose membrane lipids accumulate very long-chain polyunsaturated acids with up to 36 carbon atoms.

In vivo hemoglobin dosimetry of malonaldehyde and ethene in mice after induction of lipid peroxidation. Effects of membrane lipid fatty acid composition.

Hemoglobin (Hb) adduct determination by the N-alkyl Edman method was used for in vivo dosimetry of endogenously formed malonaldehyde (MA) and ethene in mice fed diets with different fatty acid composition and induced for lipid peroxidation with carbon tetrachloride (CCl4). In order to amplify lipid peroxidation animals were pretreated with phenobarbital (PB) and the glutathione-depleting agent DL-buthionine-(S,R)-sulfoximine (BSO). Non-treated animals raised on different diets were used as controls. Lipid peroxidation products in liver were measured as 2-thiobarbituric acid reactive compounds (TBA-C). Livers from control mice fed a soya oil based diet (rich in polyunsaturated fatty acids, diet S) showed approximately 6.5-fold higher levels of TBA-C than those from animals raised on a coconut oil based diet (mostly saturated fatty acids, diet C). The level of adducts of MA to Hb, determined as N-(3-hydroxypropyl)valine, was approximately 1.5-fold higher in animals from diet S than in animals raised on diet C. The highest increases in the levels of TBA-C and MA adducts were obtained after a simultaneous treatment of the animals with PB, BSO and CCl4. The increases of TBA-C were 1.3-fold (diet C) and 1.7-fold (diet S). The corresponding increases of MA-Hb adduct levels were 1.3- and 1.6-fold respectively, indicating an increased susceptibility of mice fed diet S to lipid peroxidation. The level of adducts from ethene, determined as N-(2-hydroxyethyl)valine, was also higher in mice from diet S than in animals fed diet C, when all treatment groups were considered. The difference was, however, only slightly significant (P less than 0.02). No difference between control and CCl4-treated animals, with regard to the ethene-Hb adduct, was found. Our results validate the use of Hb dosimetry for monitoring the effects of factors known to influence lipid peroxidation induced in vivo.

The influence of membrane lipid composition and physical properties of membrane structure and function in Acholeplasma laidlawii.

The unique properties of the A. luidlawii membrane were utilized by Steim et to show for the first time that biological membranes can undergo a gel-to-liquid-crystalline lipid phase transition similar to that previously reported for lamellar phospholipid-water systems. These workers demonstrated that when whole cells or isolated membranes are analyzed by differential scanning calorimetry (DSC), two relatively broad endothermic transitions are observed on the initial heating scan. The lowertemperature transition is fully reversible, varies markedly in position with changes in the length and degree of unsaturation of the membrane lipid fatty acyl chains, is broadened and eventually abolished by cholesterol incorporation, and exhibits a transition enthalpy characteristic of the mixed-acid synthetic phospholipids. Moreover, an endothermic transition having essentially identical properties is observed for the protein-free total membrane lipid extract dispersed in excess water or aqueous buffer, indicating that the presence of membrane proteins has little effect on the thennotropic phase behavior of most of the membrane lipids. The higher-temperature transition, in contrast, is irreversible, is independent on membrane lipid fatty acid composition or cholesterol content, and is absent in total membrane lipid extracts, indicating that it is due to an irreversible thermal denaturation of the membrane proteins. A comparison of the enthalpies of transition of the lipids in the membrane and in water dispersions indicates that at least 75% of the total membrane lipids participate in this transition. Evidence was also presented that the lipids must be predominantly in the fluid state to support normal growth. These results were later confirmed and extended by Reinert and Steim3 and by Melchior et al. ,4 who showed that the gel-to-liquid-crystalline

Modifications of membrane lipid structure and their influence on cell growth, passive permeability, and enzymatic and transport activities in Acholeplasma laidlawii B

Acholeplasma laidlawii B is a simple procaryotic microorganism, without a cell wall, whose membrane lipid fatty acid composition and cholesterol content can be dramatically modified. It is thus possible to markedly vary the temperature and cooperativity of the gel to lipid-crystalline phase transition, thereby altering the phase state and "fluidity" of the A. laidlawii membrane lipids. By varying the chain length of the exogenous fatty acids supplied, it is also possible to modify the thickness of the membrane lipid bilayer. Acholeplasma laidlawii B cell growth and most membrane functions are strongly dependent on the phase state of the membrane lipids. When gel-state lipid predominates at physiological temperatures, cell growth declines sharply, nonelectrolyte permeability exhibits a pronounced local maximum, net glucose transport is markedly reduced, and ATPase activity declines moderately. Upon complete conversion of the lipid to the gel state, cell growth ceases, passive permeability is markedly reduced, and net glucose transport is abolished, but appreciable ATPase activity remains. Provided that the membrane lipid is predominantly or exclusively in the liquid-crystalline state, cell growth and ATPase activity are almost independent of membrane lipid fatty acid composition and cholesterol content, except that cell growth is inhibited by the presence of "hyperfluid" lipid. In contrast, passive permeability and active glucose uptake are influenced by alterations in membrane lipid composition, with increases in lipid fluidity resulting in higher nonelectrolyte translocation rates. Alterations in the length of the membrane lipid hydrocarbon chains per se also appear to affect A. laidlawii growth and membrane function. Thus lipids containing fatty acids with effective chain lengths of 13 carbons or less do not support cell growth or normal enzymatic and transport activities, and lipids with effective hydrocarbon chain lengths of 19 carbons or more do not support normal cell growth.

The effect of alterations in the fluidity and phase state of the membrane lipids on the passive permeation and facilitated diffusion of glycerol in Escherichia coli.

The passive permeation and facilitated diffusion of glycerol into Escherichia coli K 1060, an unsaturated fatty acid auxotroph, were studied as a function of temperature and membrane lipid fatty acid composition using a stopped-flow spectrophotometric assay of glycerol permeation. The relative rates of glycerol passive and mediated entry were both significantly influenced by the fluidity of the membrane lipids, increasing as the gel to liquid-crystalline phase transition midpoint temperature of the membrane lipids decreased. The rate of passive glycerol permeation, but not the rate of glycerol facilitated diffusion, decreased as the membrane lipids were converted to the gel state. The apparent activation energies for passive and facilitated diffusion of glycerol, measured in cells whose membrane lipids were in the liquid-crystalline state, were 15-16 and 10-11 kcal mol-1, respectively, and neither value was significantly influenced by the fatty acid composition or fluidity of the membrane lipids. The mechanistic implications of these observations for the function of the glycerol facilitated diffusion system of E. coli are discussed.

Physiological role and membrane lipid modulation of the membrane-bound (Mg2+, na+)-adenosine triphosphatase activity in Acholeplasma laidlawii.

The membrane-bound adenosine triphosphatase (ATPase) activity of Acholeplasma laidlawii B differs in many respects from the common (Mg2+, Ca2+)-ATPase activity of higher bacteria, most notably in that it is specifically activated by Mg2+ and strongly and specifically stimulated by Na+ (or Li+). Various inhibitors diminish the ATPase activity with a concentration dependence which suggests that a single enzyme species is responsible for all of the observed ATP hydrolytic activity (both basal and Na+ stimulated). The Km for ATP is influenced by temperature but not by membrane lipid fatty acid composition. Vmax is influenced by both of these factors, showing a break in Arrhenius plots which falls below the lipid phase transition midpoint but well above the lower boundary when a phase transition occurs within the temperature range studied. The apparent energy of activation for Vmax is strongly influenced by lipid fatty acid composition both above and below the break. When whole cells of A. laidlawii B are incubated in KCl or NaCl buffers, they rapidly swell and lyse if deprived of an energy source or treated with ATPase inhibitors at concentrations which significantly inhibit enzyme activity in isolated membranes, whereas in sucrose or MgSO4 buffers of equal osmolarity, the cells are stable under these conditions. These results suggest that the membrane ATPase of A. laidlawii B is intimately associated with the membrane lipids and that it functions as a monovalent cation pump which regulates intracellular osmolarity as the (Na+, K+)-ATPase does in eucaryotes.