Acyl Phosphatidylglycerol

The Unique Phospholipidome of the Enteric Pathogen Campylobacter jejuni: Lysophosholipids Are Required for Motility at Low Oxygen Availability

In response to changes in their environment bacteria need to change both their protein and phospholipid repertoire to match environmental requirements, but the dynamics of bacterial phospholipid composition under different growth conditions is still largely unknown. In the present study, we investigated the phospholipidome of the bacterial pathogen Campylobacter jejuni. Transcription profiling on logarithmic and stationary phase grown cells of the microaerophilic human pathogen C. jejuni using RNA-seq revealed differential expression of putative phospholipid biosynthesis genes. By applying high-performance liquid chromatography tandem-mass spectrometry, we identified 203 phospholipid species representing the first determination of the phospholipidome of this pathogen. We identified nine different phospholipid classes carrying between one and three acyl chains. Phospholipidome analysis on bacteria of different ages (0-5 days) showed rapid changes in the ratio of phospholipids containing ethanolamine, or glycerol as phospholipid head group and in the number of cyclopropane bond containing fatty acids. Oxygen concentration influenced the percentage of lysophospholipids, and cyclo-propane bonds containing acyl chains. We show that large amounts of the phospholipids are lysophospholipids (30-45%), which mutant studies reveal are needed for normal C. jejuni motility at low oxygen conditions. C. jejuni possesses an unusual phospholipidome that is highly dynamic in response to environmental changes.

Stairway to Asymmetry: Five Steps to Lipid-Asymmetric Proteoliposomes

Membrane proteins are embedded in a complex lipid environment that influences their structure and function. One key feature of nearly all biological membranes is a distinct lipid asymmetry. However, the influence of membrane asymmetry on proteins is poorly understood, and novel asymmetric proteoliposome systems are beneficial. To our knowledge, we present the first study on a multispanning protein incorporated in large unilamellar liposomes showing a stable lipid asymmetry. These asymmetric proteoliposomes contain the Na+/H+ antiporter NhaA from Salmonella Typhimurium. Asymmetry was introduced by partial, outside-only exchange of anionic phosphatidylglycerol (PG), mimicking this key asymmetry of bacterial membranes. Outer-leaflet and total fractions of PG were determined via ζ-potential (ζ) measurements after lipid exchange and after scrambling of asymmetry. ζ-Values were in good agreement with exclusive outside localization of PG. The electrogenic Na+/H+ antiporter was active in asymmetric liposomes, and it can be concluded that reconstitution and generation of asymmetry were successful. Lipid asymmetry was stable for more than 7 days at 23°C and thus enabled characterization of the Na+/H+ antiporter in an asymmetric lipid environment. We present and validate a simple five-step protocol that addresses key steps to be taken and pitfalls to be avoided for the preparation of asymmetric proteoliposomes: 1) optimization of desired lipid composition, 2) detergent-mediated protein reconstitution with subsequent detergent removal, 3) generation of lipid asymmetry by partial exchange of outer-leaflet lipid, 4) verification of lipid asymmetry and stability, and 5) determination of protein activity in the asymmetric lipid environment. This work offers guidance in designing asymmetric proteoliposomes that will enable researchers to compare functional and structural properties of membrane proteins in symmetric and asymmetric lipid environments.

Salmonella enterica Serovar Typhimurium Uses PbgA/YejM To Regulate Lipopolysaccharide Assembly during Bacteremia

Salmonella enterica serovar Typhimurium (S Typhimurium) relies upon the inner membrane protein PbgA to enhance outer membrane (OM) integrity and promote virulence in mice. The PbgA transmembrane domain (residues 1 to 190) is essential for viability, while the periplasmic domain (residues 191 to 586) is dispensable. Residues within the basic region (residues 191 to 245) bind acidic phosphates on polar phospholipids, like for cardiolipins, and are necessary for salmonella OM integrity. S Typhimurium bacteria increase their OM cardiolipin concentrations during activation of the PhoPQ regulators. The mechanism involves PbgA's periplasmic globular region (residues 245 to 586), but the biological role of increasing cardiolipins on the surface is not understood. Nonsynonymous polymorphisms in three essential lipopolysaccharide (LPS) synthesis regulators, lapB (also known as yciM), ftsH, and lpxC, variably suppressed the defects in OM integrity, rifampin resistance, survival in macrophages, and systemic colonization of mice in the pbgAΔ191-586 mutant (in which the PbgA periplasmic domain from residues 191 to 586 is deleted). Compared to the OMs of the wild-type salmonellae, the OMs of the pbgA mutants had increased levels of lipid A-core molecules, cardiolipins, and phosphatidylethanolamines and decreased levels of specific phospholipids with cyclopropanated fatty acids. Complementation and substitution mutations in LapB and LpxC generally restored the phospholipid and LPS assembly defects for the pbgA mutants. During bacteremia, mice infected with the pbgA mutants survived and cleared the bacteria, while animals infected with wild-type salmonellae succumbed within 1 week. Remarkably, wild-type mice survived asymptomatically with pbgA-lpxC salmonellae in their livers and spleens for months, but Toll-like receptor 4-deficient animals succumbed to these infections within roughly 1 week. In summary, S Typhimurium uses PbgA to influence LPS assembly during stress in order to survive, adapt, and proliferate within the host environment.

Salmonella Tol-Pal Reduces Outer Membrane Glycerophospholipid Levels for Envelope Homeostasis and Survival during Bacteremia

Salmonellae regulate membrane lipids during infection, but the exact proteins and mechanisms that promote their survival during bacteremia remain largely unknown. Mutations in genes encoding the conserved Salmonella enterica serovar Typhimurium (S. Typhimurium) Tol-Pal apparatus caused the outer membrane (OM) sensor lipoprotein, RcsF, to become activated. The capsule activation phenotype for the mutants suggested that Tol-Pal might influence envelope lipid homeostasis. The mechanism involves reducing OM glycerophospholipid (GPL) levels, since the mutant salmonellae similarly accumulated phosphatidylglycerols (PGl) and phosphatidylethanolamines (PE) within the OM in comparison to the wild type. The data support the Escherichia coli model, whereby Tol-Pal directs retrograde GPL translocation across the periplasm. The S. Typhimurium mechanism involves contributions from YbgC, a cytoplasmic acyl coenzyme A (acyl-CoA) thioesterase, and CpoB, a periplasmic TolA-binding protein. The functional relationship between Tol-Pal and YbgC and CpoB was previously unresolved. The S. Typhimurium Tol-Pal proteins contribute similarly toward promoting OM-GPL homeostasis and Rcs signaling inactivity but differently toward promoting bacterial morphology, rifampin resistance, survival in macrophages, and survival in mice. For example, tolQ, tolR, tolA, and cpoB mutants were significantly more attenuated than ybgC, tolB, and pal mutants in a systemic mouse model of disease. Therefore, key roles exist for TolQ, TolR, TolA, and CpoB during murine bacteremia, which are independent of maintaining GPL homeostasis. The ability of TolQR to channel protons across the inner membrane (IM) is necessary for S. Typhimurium TolQRA function, since mutating conserved channel-facing residues rendered TolQ ineffective at rescuing deletion mutant phenotypes. Therefore, Tol-Pal promotes S. Typhimurium survival during bacteremia, in part, by reducing OM GPL concentrations, while TolQRA and CpoB enhance systemic virulence by additional mechanisms.

Nutrient depletion-induced production of tri-acylated glycerophospholipids in Acinetobacter radioresistens

Bacteria inhabit a vast range of biological niches and have evolved diverse mechanisms to cope with environmental stressors. The genus Acinetobacter comprises a complex group of Gram-negative bacteria. Some of these bacteria such as A. baumannii are nosocomial pathogens. They are often resistant to multiple antibiotics and are associated with epidemic outbreaks. A. radioresistens is generally considered to be a commensal bacterium on human skin or an opportunistic pathogen. Interestingly, this species has exceptional resistance to a range of environmental challenges which contributes to its persistence in clinical environment and on human skin. We studied changes in its lipid composition induced by the onset of stationary phase. This strain produced triglycerides (TG) as well as four common phospholipids: phosphatidylethanolamine (PE), phosphatidylglycerol (PG), cardiolipin (CL) and lysocardiolipin (LCL). It also produced small amounts of acyl-phosphatidylglycerol (APG). As the bacterial growth entered the stationary phase, the lipidome switched from one dominated by PE and PG to another dominated by CL and LCL. Surprisingly, bacteria in the stationary phase produced N-acyl-phosphatidylethanolamine (NAPE) and another rare lipid we tentatively name as 1-phosphatidyl-2-acyl-glycero-3-phosphoethanolamine (PAGPE) based on tandem mass spectrometry. It is possible these tri-acylated lipids play an important role in coping with nutrient depletion.

Emerging roles for anionic non-bilayer phospholipids in fortifying the outer membrane permeability barrier

Lately, researchers have been actively investigating Escherichia coli lptD mutants, which exhibit reduced transport of lipopolysaccharide to the cell surface. In this issue of the Journal of Bacteriology, Sutterlin et al. (H. A. Sutterlin, S. Zhang, and T. J. Silhavy, J. Bacteriol. 196:3214-3220, 2014) now reveal an important functional role for phosphatidic acid in fortifying the outer membrane permeability barrier in certain lptD mutant backgrounds. These findings come on the heels of the first reports of two LptD crystal structures, which now provide a structural framework for interpreting lptD genetics.

PhoPQ regulates acidic glycerophospholipid content of the Salmonella Typhimurium outer membrane

Gram-negative bacteria have two lipid membranes separated by a periplasmic space containing peptidoglycan. The surface bilayer, or outer membrane (OM), provides a barrier to toxic molecules, including host cationic antimicrobial peptides (CAMPs). The OM comprises an outer leaflet of lipid A, the bioactive component of lipopolysaccharide (LPS), and an inner leaflet of glycerophospholipids (GPLs). The structure of lipid A is environmentally regulated in a manner that can promote bacterial infection by increasing bacterial resistance to CAMP and reducing LPS recognition by the innate immune system. The gastrointestinal pathogen, Salmonella Typhimurium, responds to acidic pH and CAMP through the PhoPQ two-component regulatory system, which stimulates lipid A remodeling, CAMP resistance, and intracellular survival within acidified phagosomes. Work here demonstrates that, in addition to regulating lipid A structure, the S. Typhimurium PhoPQ virulence regulators also regulate acidic GPL by increasing the levels of cardiolipins and palmitoylated acylphosphatidylglycerols within the OM. Triacylated palmitoyl-PG species were diminished in strains deleted for the PhoPQ-regulated OM lipid A palmitoyltransferase enzyme, PagP. Purified PagP transferred palmitate to PG consistent with PagP acylation of both lipid A and PG within the OM. Therefore, PhoPQ coordinately regulates OM acidic GPL with lipid A structure, suggesting that GPLs cooperate with lipid A to form an OM barrier critical for CAMP resistance and intracellular survival of S. Typhimurium.

Characterization of acylphosphatidylglycerols from Salmonella typhimurium by tandem mass spectrometry with electrospray ionization

Acylphosphatidylglycerol (Acyl-PG), a polar lipid class containing three fatty acyl groups, was isolated from Salmonella bacteria and characterized by tandem quadrupole and quadrupole ion-trap mass spectrometric methods with electrospray ionization. The structural characterization of the acyl-PG with various acyl groups (A-B/C-PG, where A not equal B not equal C) is based on the findings that the carboxylate anions (R(x)CO(2)(-)) arising from sn-2 (R(2)CO(2)(-)) is more abundant than that arising from sn-3' (R(3')CO(2)(-)), which is much more abundant than that arising from sn-1 (R(1)CO(2)(-)). This information provides a simple method for determination of the fatty acyl moieties and their positions in the molecule. The structural identification of the molecule can also be achieved by the findings that the fragment ion reflecting the ketene loss at sn-2 is more prominent than that reflecting the acid loss (i.e., [M - H - R'(2)CH=CO](-) > [M - H - R(2)CO(2)H](-)), while the ion arising from acid loss at sn-1 or sn-3' is, respectively, more abundant than the corresponding ketene loss (i.e., [M - H - R(1)CO(2)H](-) > [M - H - R'(1)CH=CO](-); [M - H - R(3')CO(2)H](-) > [M - H -R'(3')CH=CO](-)). The identity of the acyl moiety at sn-3' can be confirmed by an acyl-glycerophosphate anion observed in the product-ion spectrum obtained with a triple-stage quadrupole (TSQ) instrument, but not in that obtained with an ion-trap mass spectrometer (ITMS). However, the MS(2)-spectrum obtained with an ITMS is featured by the ion series that abundances of [M - H - R'(2)CH=CO - R(3)CO(2)H - 74](-) > [M - H - R'(2)CH=CO - R(1)CO(2)H - 74](-) z.Gt; [M - H - R'(1(or 3'))CH=CO - R(3'(or 1))CO(2)H - 74](-). This information also facilitates structural elucidation of the acyl-PG subclass that contains various acyl substituents. Structural identifications of molecular species having two identical fatty acyl substituents at sn-1, sn-2, or sn-3' or consisting of more than one isomeric structures are also demonstrated. The identities of the minor isomeric species in the molecules can be revealed by the aforementioned structural information arising from the various ion series combined.

Acidic glycerol lipids of Trichomonas vaginalis and Tritrichomonas foetus

The isolation and characterization of acidic lipids from both Trichomonas vaginalis and Tritrichomonas foetus have been carried out using radiolabeling, a combination of high performance liquid and thin layer chromatographic techniques, and mass spectrometry. Unique among the eukaryotes, these organisms produce phosphatidylglycerols and O-acyl phosphatidylglycerol-like compounds. In this study, the molecular weight distributions of the phosphatidylglycerols and acyl phosphatidylglycerols were determined by negative-ion liquid secondary ionization mass spectrometry (LSIMS) and the fatty acyl groups within each molecular species were assessed by collision-induced decomposition tandem mass spectrometry (CID MS/MS). Both species were found to contain primarily oleic acid in the sn-2 position. The lipids of T. vaginalis had approximately equal amounts of C16 and C18 in the sn-1 position, with varying degrees of unsaturation, especially in the C18 species. The T. foetus lipids had C18 almost exclusively, but also varied in the unsaturation. Other acidic lipids included inositol phosphosphingolipids and inositol diphosphosphingolipids.

Intracellular serine-protease zymogen, factor C, from horseshoe crab hemocytes. Its activation by synthetic lipid A analogues and acidic phospholipids

An intracellular clotting factor, factor C, found in the horseshoe crab hemocytes is a lipopolysaccharide-sensitive serine-protease zymogen, which participates in the initiation of the hemolymph clotting system [T. Nakamura et al. (1986) Eur. J. Biochem. 154, 511-521]. The subsequent study of this zymogen, using various synthetic lipid A analogues, revealed that the zymogen factor C is rapidly activated by acylated (beta 1-6)-D-glucosamine disaccharide bisphosphate (synthetic Escherichia coli-type lipid A), and the corresponding 4'-monophosphate analogues. However, the corresponding non-phosphorylated lipid A did not activate factor C, indicating that a phosphate ester group linked with the (beta 1-6)-D-glucosamine disaccharide backbone is required for the zymogen activation. During these studies we also found that the zymogen factor C is significantly activated by acidic phospholipids, such as phosphatidylinositol, phosphatidylglycerol and cardiolipin, but not at all by neutral phospholipids. The rate of this activation, however, was affected markedly by ionic strength in the reaction mixture, although such an effect was not observed in the lipid-A-mediated activation of factor C. A variety of negatively charged surfaces, such as sulfatide, dextran sulfate and ellagic acid, which are known as typical initiators for activation of the mammalian intrinsic clotting system, did not show any effect on the zymogen factor C activation. These results suggest that lipid A is the most effective trigger to initiate the activation of the horseshoe crab hemolymph clotting system.

Concurrent disappearance of N-acylethanolamine glycerophospholipids and phagolysosomes enriched in N-acylethanolamine glycerophospholipids as Dictyostelium discoideum cells aggregate

As the cellular slime mold, Dictyostelium discoideum, undergoes development, a phospholipid fraction containing 80% N-acylethanolamine glycerophospholipids (NAEGPs) and 20% acylphosphatidylglycerol (APG) disappears during the aggregation stage. In this study, the subcellular distribution of that NAEGP phospholipid fraction and the precise time period of disappearance of the fraction were determined. The content of the NAEGP fraction was determined in aggregating cells at 2-h intervals from the beginning of the developmental phase through 14 h, when the cells were completely aggregated. The NAEGP fraction comprised about 8% of the phospholipids in amoebae just starting the development cycle and about 12% in cells between 2 and 6 h of development; then its level decreased until it could not be detected at 12 and 14 h of development. The mole percentage of the total lipid phosphate in the NAEGP fraction was determined in isolated subcellular organelles. The phagolysosomes were enriched in the NAEGP fraction 1.7-2-fold over the level found in the amoebae and about 8-fold over the level in fractions highly enriched in the plasma membrane, mitochondria or peroxisomes. The content of phagolysosomes was determined by electron microscopy of aggregating cells. The amoebae contained large amounts of phagolysosomes up to 6 h of development, and then they gradually disappeared between 6 and 12 h of development. This combination of quantitative phospholipid analysis, subcellular organelle isolation and electron microscopy has revealed that in D. discoideum amoebae, the phagolysosomes were selectively enriched in the NAEGP fraction and both the NAEGP-enriched phagolysosomes and the NAEGPs disappeared concurrently between 6 and 12 h of development.

Polar lipids from the radiation resistant bacterium Deinococcus radiodurans: structural investigations on glucosaminyl and N-acetyl glucosaminyl lipids

Deinococcus radiodurans, although a gram-positive bacterium, has a complex cell wall with multiple layers and associates to this structural particularity, a quite unusual lipid composition for gram-positive bacteria. The conventional phospholipids (phosphatidyl ethanolamine, phosphatidyl choline, phosphatidyl glycerol...) are absent. Among the nine polar lipids detected in the R1 Anderson strain, three are glycolipids only one is a phospholipid, the other ones are glycophospholipids. One of the latter compounds contains one free amino group. Analysis by aminoacid autoanalyser enables to identify glucosamine in one glycolipid and in two glycophospholipids. Sugar analysis by gas-liquid chromatography after acid methanolysis and trifluoroacetylation, reveals the occurrence of N-acetyl glucosaminyl residues in one glycolipid and in one phospholipid. The following identification for the two lipids of D. radiodurans is proposed: phosphatidyl glucosaminyl glycerol and phosphatidyl N-acetyl glucosaminyl glycerol.

Identification of N-acylethanolamine phosphoglycerides and acylphosphatidylglycerol as the phospholipids which disappear as Dictyostelium discoideum cells aggregate

The cellular slime mold Dictyostelium discoideum contains a phospholipid fraction which comprises 10% of the phospholipids in the early developing amoebae and disappears during the aggregation stage of development. As a first step in studying its metabolism, the composition of the fraction has been determined. It was easily isolated by preparative silicic acid thin-layer chromatography because its Rf was considerably higher than most commonly encountered phospholipids. Its Rf was the same as synthetic phosphatidyl-N-acylethanolamine and synthetic acylphosphatidylglycerol (also called semilysobisphosphatidic acid). Strong absorption peaks characteristic of amide bonds in the infrared spectrum of the isolated D. discoideum phospholipid showed that N-acylethanolamine phosphoglycerides were present. The presence of acylphosphatidylglycerol was revealed when mild alkaline hydrolysis of the lipid fraction produced glycerophosphorylglycerol as the only water-soluble, phosphate-containing product. The composition of the fraction was determined by chemical analysis and thin-layer chromatography of the intact phospholipids and their partially or completely hydrolyzed products. The composition of the fraction was 30% diacylglycerophosphoryl-N-acylethanolamine, 50% alkenylacylglycerophosphoryl-N-acylethanolamine, and 20% acylphosphatidylglycerol. The stereoconfiguration of the glycerophosphorylglycerol moiety of the acylphosphatidylglycerol was found to be sn-3-glycerophosphoryl-sn-1'-glycerol.

On the relationship between glycerophosphoglycolipids and lipoteichoic acids in Gram-positive bacteria. I. The occurrence of phosphoglycolipids

1. Gram-positive bacteria out of the families of Streptococcaceae, Lactobacillaceae, Micrococcaceae and Bacillaceae were investigated with respect to the occurrence and the concentration of phosphoglycolipids. 2. Phosphatidylglycolipids occur exclusively in group D Streptococci and in Streptococcus hemolyticus D-58. Phosphatidyl-alpha-kojibiosyldiacylglycerol, the prevalent species, accounts for up to 28% of the polar lipids. The related glycerophospho-phosphatidyl-alpha-kojibiosyldiacylglycerol is restricted to Streptococcus faecalis. 3. Glycerophosphoglycolipids, usually minor components, comprise thirteen compounds most of which have so far not been described. Except Micrococcus lysodeikticus all examined bacteria contained one or more glycerophosphoglycolipids. Their occurrence parallels, therefore, that of lipoteichoic acids, which supports the hypothesis of a metabolic relationship between these two membrane components.

Stereoconfiguration of bisphosphatidic and semilysobisphosphatidic acids from cultured hamster fibroblasts (BHK cells)

Monolayers of hamster fibroblasts (BHK cells) were incubated in Eagle's minimal essential medium under conditions where an increase in the levels of all cellular bisphosphatidic acids takes place. Bisphosphatidic acid and semilysobisphosphatidic were isolated from these cells and subjected to strong alkaline hydrolysis. Stereochemical analysis of the hydrolysis products revealed that the majority of the molecules of both lipids are derivatives of sn-1-glycerophospho-sn-1'-glycerol, the structure previously found to be the "backbone" of lysobisphosphatidic acid, (bis(monoacylglycerol)phosphate) from BHK cells and other sources. This finding suggests a close metabolic relationship between the three bisphosphatidic acid derivatives of BHK cells.

Identification of acyl phosphatidylglycerol as a minor phospholipid of Pseudomonas BAL-31

Compound X, a minor phospholipid of Pseudomonas BAL-31 and bacteriophage PM2, has been identified as X-3-phosphatidyl-1'-(3'-acyl)-glycerol, or acyl phosphatidylglycerol. The water-soluble product obtained by mild alkaline hydrolysis showed the same RF value as that of glycerophosphoryl-glycerol. The chemical analysis gave the ratio 1 : 3 : 2 for phosphate-acyl ester-glycerol. The position of the third acyl group was determined by nuclear magnetic resonance techniques.

Novel lipids of Butyrivibrio spp

(1) An analysis has been conducted of the lipids present in three obligately anaerobic bacteria isolated from the ovine rumen belonging to the genus Butyrivibrio. Two of these organisms are rich in phospholipase (A1 + A2) activity, and appear to be different strains of the species fibrisolvens. (2) The only N-containing lipids comprise N-acyl-phosphatidylethanolamine occurring as a minor component in all organisms and a new lipid, diglyceride galactosylphosphorylethanolamine in one of these. (3) All three organisms contained the n-butyryl ester of phosphatidyl-glycerol and in one this represented the major phospholipid present. Valeryl, iso-valeryl, propionyl and myristoyl esters of phosphatidylglycerol were also detected. (4) Two organisms contained glycerylphosphorylgalactosyldiglyceride and one of these also contained a large proportion of a less polar galactophospholipid which is probably a diacyl derivative of the former lipid. (5) All three organisms contained monogalactofuranosyl diglyceride and from one a n-butyryl ester of this galactolipid was isolated. (6) In all of the lipids examined the "diglyceride' moiety consisted almost entirely of plasmalogenic diglyceride (alk-1-enyl, acyl, glycerol).

Studies on the biosynthesis of acylphosphatidylglycerol in Escherichia coli B and B/r

The present study has demonstrated that one molecule of acylphosphatidylglycerol was synthesized from two molecules of phosphatidylgycerol by the transacylation reaction in which phosphatidylglycerol acted both as an acyl donor and an acceptor. Phosphatidylethanolamine was identified as an another acyl donor, participating in acylphosphatidylglycerol formation. These results are discussed in terms of a new pathway for the turnover of phosphatidylglycerol in Escherichia coli.