Arabidopsis phosphatidylglycerophosphate phosphatase 1 involved in phosphatidylglycerol biosynthesis and photosynthetic function

Phosphatidylglycerol (PG) is an indispensable lipid constituent of photosynthetic membranes, whose function is essential in photosynthetic activity. In higher plants, the biological function of the last step of PG biosynthesis remains elusive because an enzyme catalyzing this reaction step, namely phosphatidylglycerophosphate phosphatase (PGPP), has been a missing piece in the entire glycerolipid metabolic map. Here, we report the identification and characterization of AtPGPP1 encoding a PGPP in Arabidopsis thaliana. Heterologous expression of AtPGPP1 in yeast Δgep4 complemented growth phenotype and PG-producing activity, suggesting that AtPGPP1 encodes a functional PGPP. The GUS reporter assay showed that AtPGPP1 was preferentially expressed in hypocotyl, vasculatures, trichomes, guard cells, and stigmas. A subcellular localization study with GFP reporter indicated that AtPGPP1 is mainly localized at chloroplasts. A T-DNA-tagged knockout mutant of AtPGPP1, designated pgpp1-1, showed pale green phenotype with reduced PG and chlorophyll contents but no defect in embryo development. In the pgpp1-1 mutant, ultrastructure of plastids indicated defective development of chloroplasts and measurement of photosynthetic parameters showed impaired photosynthetic activity. These results suggest that AtPGPP1 is a primary plastidic PGPP required for PG biosynthesis and photosynthetic function in Arabidopsis.

Phosphatidylglycerol-derived phospholipids have a universal, domain-crossing role in stress responses

Phosphatidylglycerol and phospholipids derived from it are widely distributed throughout the three domains of life. Cardiolipin is the best characterized of these phospholipids, and plays a key role in the response to environmental variations. Phosphatidylglycerol-derived phospholipids confer cell membranes with a wide range of responses, including changes in surface charge, fluidity, flexibility, morphology, biosynthesis and remodeling, that adapt the cell to these situations. Furthermore, the synthesis and remodeling of these phospholipids is finely regulated, highlighting the importance of these lipids in cell homeostasis and responses during stressful situations. In this article, we review the most important roles of these anionic phospholipids across domains, focusing on the biophysical basis by which these phospholipids are used in stress responses.

Isolation and characterization of a phosphatidylglycerophosphate phosphatase1, PGPP1, in Chlamydomonas reinhardtii

Phosphatidylglycerol (PG) is the exclusive phospholipid synthesized in chloroplasts and plays important roles in photosynthesis. However, phosphatidylglycerophosphate phosphatase (PGPP), which catalyzes the final step of PG biosynthesis, is a missing piece in photosynthetic eukaryotes. Here, we isolated a previously uncharacterized haloacid dehalogenase-like phosphatase, designated CrPGPP1, as a putative PGPP in Chlamydomonas reinhardtii. CrPGPP1 complemented growth and lipid compositional defects in Δgep4, a yeast mutant of PGPP, which indicates that CrPGPP1 is a functional PGPP. Two aspartic acid residues, which are both essential for the yeast PGPP (Gep4p) activity, are also conserved in the putative catalytic motif of CrPGPP1. Site-specific mutagenesis showed that the first but not the second aspartic acid residue was required for CrPGPP1 to complement the growth defect of Δgep4 mutant, which highlights the distinct molecular features of CrPGPP1. Our results suggest that CrPGPP1 is a functional PGPP in C. reinhardtii, for the first PGPP in photosynthetic eukaryotes.

Formation of oxidized phosphatidylinositol and 12-oxo-phytodienoic acid containing acylated phosphatidylglycerol during the hypersensitive response in Arabidopsis

Plant membranes are composed of a wide array of polar lipids. The functionality of these extends far beyond a pure structural role. Membrane lipids function as enzyme co-factors, establish organelle identity and as substrates for enzymes such as lipases and lipoxygenases. Enzymatic degradation or oxidation (enzymatic or non-enzymatic) of membrane lipids leads to the formation of a diverse group of bioactive compounds. Plant defense reactions provoked by pathogenic microorganisms are often associated with substantial modifications of the lipidome. In this study, we profiled changes in phospholipids during the hypersensitive response triggered by recognition of the bacterial effector protein AvrRpm1 in Arabidopsis thaliana. A simple and robust LC-MS based method for profiling plant lipids was designed to separate all the major species of glycerolipids extracted from Arabidopsis leaf tissue. The method efficiently separated several isobaric and near isobaric lipid species, which otherwise are difficult to quantify in direct infusion based profiling. In addition to the previously reported OPDA-containing galactolipids found to be induced during hypersensitive response in Arabidopsis, three OPDA-containing sulfoquinovosyl diacylglycerol species, one phosphatidylinositol species as well as two acylated OPDA-containing phosphatidylglycerol species were found to accumulate during the hypersensitive response in Arabidopsis. Our study confirms and extends on the notion that the hypersensitive response in Arabidopsis triggers a unique profile of Allene Oxide Synthase dependent oxidation of membrane lipids. Primary targets of this oxidation seem to be uncharged and anionic lipid species.

The lack of L-PG production and the repercussions of it in regards to M. Tuberculosis interactions with mononuclear phagocytes

The lysine connection with phosphatidylglycerol (PG) alters the M. tuberculosis(Mtb) surface charge, and consequently it may decrease the bacterial vulnerability to antimicrobial action of the immune cells. The aim of the study was to assess the significance of PG lysinylation in the Mtb interactions with mononuclear phagocytes. Both the Mtb strain with deletion of lysX gene (Mtb-lysX) which is responsible for PG lysinylation as well as the complemented strain (Mtb-compl) was used to infect human blood monocytes or THP-1 cells. The monocytes were obtained by MACS technique, or THP-1 cells. The Mtb-lysX strain has exhibited the enhanced sensitivity to HNP 1-3. However, it was not susceptible to bactericidal action of cathepsin G. The LysX deletion did not influence the Mtb ability of monocyte induction to IL-10 secretion. The intra- and extracellular expression of MHC-II was similarly reduced after the Mtb-lysX or Mtb-Rv infections. Noticeably significant is that the Mtb strain with deleted lysX has not affected the intensity of the gene expression of cathepsin G compared to the uninfected monocytes. That is the clear contrast to what the Mtb-Rv strain has proved. The obtained results suggest that the Mtb ability to lysinylate PG is a participatory element in mycobacterial strategy of survival inside phagocytic cells. However, the extended studies are needed to determine its influence on the other immune cells and define its role in the developing of Mtb infection.

The two-domain LysX protein of Mycobacterium tuberculosis is required for production of lysinylated phosphatidylglycerol and resistance to cationic antimicrobial peptides

The well-recognized phospholipids (PLs) of Mycobacterium tuberculosis (Mtb) include several acidic species such as phosphatidylglycerol (PG), cardiolipin, phosphatidylinositol and its mannoside derivatives, in addition to a single basic species, phosphatidylethanolamine. Here we demonstrate that an additional basic PL, lysinylated PG (L-PG), is a component of the PLs of Mtb H37Rv and that the lysX gene encoding the two-domain lysyl-transferase (mprF)-lysyl-tRNA synthetase (lysU) protein is responsible for L-PG production. The Mtb lysX mutant is sensitive to cationic antibiotics and peptides, shows increased association with lysosome-associated membrane protein-positive vesicles, and it exhibits altered membrane potential compared to wild type. A lysX complementing strain expressing the intact lysX gene, but not one expressing mprF alone, restored the production of L-PG and rescued the lysX mutant phenotypes, indicating that the expression of both proteins is required for LysX function. The lysX mutant also showed defective growth in mouse and guinea pig lungs and showed reduced pathology relative to wild type, indicating that LysX activity is required for full virulence. Together, our results suggest that LysX-mediated production of L-PG is necessary for the maintenance of optimal membrane integrity and for survival of the pathogen upon infection.

Gammaproteobacteria as a possible source of eicosapentaenoic acid in anoxic intertidal sediments

Eicosapentaenoic acid (EPA; n-20:5omega3) was found to be a constituent of phospholipids in three mesophilic strains of Gammaproteobacteria, which were isolated from anoxic most probable number series prepared with sediments from an intertidal flat of the German North Sea coast. Their partial 16S rRNA gene sequences identified the isolates as close relatives of Shewanella colwelliana, Vibrio splendidus, and Photobacterium lipolyticum. So far, eicosapentaenoic acid has mainly been reported to occur in eukaryotes and some piezophilic or psychrophilic bacteria. With decreasing temperature, relative contents of EPA (up to 14% of total fatty acids) increased in all strains. Additionally, Shewanella and Vibrio spp. showed a significant increase in monounsaturated fatty acids with lower growth temperature. Analysis of the phospholipid compositions revealed that EPA was present in all three major phospholipid types, namely, phosphatidyl glycerol (PG), cardiolipin and phosphatidyl ethanolamine (PE). However, EPA was enriched in PG and cardiolipin relative to PE. In the tidal flat sediments from which the isolates were obtained, substantial amounts of EPA-containing PG were detected, whereas other typical microeukaryotic phospholipids-being also a possible source of EPA-were abundant at the sediment surface but were present in clearly lower amounts in the anoxic layers beneath 5 cm depth. Therefore, the EPA-containing PG species in the deeper layers in these sediments may indicate the presence of Gammaproteobacteria closely related to the isolates. These bacteria appear to be an important source of EPA in buried, anoxic sediments beneath the layers harboring significant populations of benthic eukaryotes.

Monitoring Lys-tRNA(Lys) phosphatidylglycerol transferase activity

In some bacteria Lys-tRNA(Lys) is used both in translation and for the specific addition of Lys to phosphatidylglycerol in the cytoplasmic membrane. This reaction is catalyzed by the membrane protein MprF, and the lysyl-phosphatidylglycerol formed contributes to the resistance of these bacteria to various cationic antibacterial molecules. Obtaining proteins and reconstituting an in vitro system mimicking membrane conditions is a major challenge to studying the function of membrane proteins, especially when labile substrates such as Lys-tRNA(Lys) are required. Here we report methods to obtain a stable enriched membrane fraction containing MprF, and the techniques necessary to quantitatively monitor its activity in vitro and in vivo.

The essential role of phosphatidylglycerol in photosynthesis

Since the first identification of phosphatidylglycerol in Scenedesmus by Benson and Maruo in 1958, researchers have studied many biological functions of this phospholipid. Genetic, biochemical, and structural studies of photosynthetic organisms have revealed that phosphatidylglycerol is crucial to the photosynthetic transport of electrons, the development of chloroplasts, and tolerance to chilling. In this review, we summarize our present understanding of the biochemical and physiological functions of phosphatidylglycerol in cyanobacteria and higher plants.

Channeling of eukaryotic diacylglycerol into the biosynthesis of plastidial phosphatidylglycerol

Plastidial glycolipids contain diacylglycerol (DAG) moieties, which are either synthesized in the plastids (prokaryotic lipids) or originate in the extraplastidial compartment (eukaryotic lipids) necessitating their transfer into plastids. In contrast, the only phospholipid in plastids, phosphatidylglycerol (PG), contains exclusively prokaryotic DAG backbones. PG contributes in several ways to the functions of chloroplasts, but it is not known to what extent its prokaryotic nature is required to fulfill these tasks. As a first step toward answering this question, we produced transgenic tobacco plants that contain eukaryotic PG in thylakoids. This was achieved by targeting a bacterial DAG kinase into chloroplasts in which the heterologous enzyme was also incorporated into the envelope fraction. From lipid analysis we conclude that the DAG kinase phosphorylated eukaryotic DAG forming phosphatidic acid, which was converted into PG. This resulted in PG with 2-3 times more eukaryotic than prokaryotic DAG backbones. In the newly formed PG the unique Delta3-trans-double bond, normally confined to 3-trans-hexadecenoic acid, was also found in sn-2-bound cis-unsaturated C18 fatty acids. In addition, a lipidomics technique allowed the characterization of phosphatidic acid, which is assumed to be derived from eukaryotic DAG precursors in the chloroplasts of the transgenic plants. The differences in lipid composition had only minor effects on measured functions of the photosynthetic apparatus, whereas the most obvious phenotype was a significant reduction in growth.

Impaired photosynthesis in phosphatidylglycerol-deficient mutant of cyanobacterium Anabaena sp. PCC7120 with a disrupted gene encoding a putative phosphatidylglycerophosphatase

Phosphatidylglycerol (PG) is a ubiquitous phospholipid in thylakoid membranes of cyanobacteria and chloroplasts and plays an important role in the structure and function of photosynthetic membranes. The last step of the PG biosynthesis is dephosphorylation of phosphatidylglycerophosphate (PGP) catalyzed by PGP phosphatase. However, the gene-encoding PGP phosphatase has not been identified and cloned from cyanobacteria or higher plants. In this study, we constructed a PG-deficient mutant from cyanobacterium Anabaena sp. PCC7120 with a disrupted gene (alr1715, a gene for Alr1715 protein, GenBank accession no. BAB78081) encoding a putative PGP phosphatase. The obtained mutant showed an approximately 30% reduction in the cellular content of PG. Following the reduction in the PG content, the photoautotrophical growth of the mutant was restrained, and the cellular content of chlorophyll was decreased. The decreases in net photosynthetic and photosystem II (PSII) activities on a cell basis also occurred in this mutant. Simultaneously, the photochemical efficiency of PSII was considerably declined, and less excitation energy was transferred toward PSII. These findings demonstrate that the alr1715 gene of Anabaena sp. PCC7120 is involved in the biosynthesis of PG and essential for photosynthesis.

Phosphatidylglycerol biosynthesis in chloroplasts of Arabidopsis mutants deficient in acyl-ACP glycerol-3- phosphate acyltransferase

The biosynthesis of phosphatidylglycerol represents a central pathway in lipid metabolism in all organisms. The enzyme catalyzing the first reaction of the pathway in the plastid, glycerol-3-phosphate acyl-acyl carrier protein acyltransferase, is thought to be encoded in Arabidopsis by the ATS1 locus. A number of genetic mutants deficient in this activity have been described. However, the corresponding mutant alleles have not yet been analyzed at the molecular level and a causal relationship between the mutant phenotypes and a deficiency at the ATS1 locus has not been established. The presence in all known ats1 mutants of near wild-type amounts of phosphatidylglycerol raised the question of whether an alternative pathway of phosphatidylglycerol assembly in the plastid exists. However, detailed analysis of several independent ats1 mutant alleles revealed that all are leaky. Reduction by RNAi of ats1-1 RNA levels in the ats1-1 mutant background led to a more severe growth phenotype (small green plants and reduced seed set), but did not decrease the relative amount of phosphatidylglycerol. In contrast, when the amount of ATS2 mRNA encoding the plastidic lysophosphatidic acid acyltransferase catalyzing the second reaction of the pathway was reduced by RNAi in the ats1-1 mutant background, phosphatidylglycerol amounts decreased, leading to a growth phenotype (small pale-yellow plants) that is reminiscent of the pgp1-1 mutant deficient in a late step of plastidic phosphatidylglycerol biosynthesis. These observations indicate coordinated regulation of plastid lipid metabolism and plant development.

[Changes in the composition of anionic membrane phospholipids influence the protein secretion and biogenesis of cell envelope in Escherichia coli]

The secretion of alkaline phosphatase (PhoA) and peculiarities of biogenesis of the cell envelope were studied in Escherichia coli strains HD30/pHD 102 and HDL11 with controlled synthesis of anionic phospholipids, phosphatidylglycerol, and cardiolipin. Inactivation of the pgsA gene encoding the synthesis of anionic phospholipids or changes in the regulation of its expression by an environmental factor caused changes in the metabolism and composition of membrane phospholipids, which resulted in a decrease in the secretion of alkaline phosphatase through the cytoplasmic membrane and an increase in PhoA secretion from the periplasm into the culture medium. A conforming increase was observed in exopolysaccharide secretion, as well as a decrease in the contents of lipopolysaccharide and lipopolyprotein of the outer membrane that determine the membrane barrier properties. The results obtained testify that anionic phospholipids play a significant role in protein secretion and are probably involved in the interrelation between the protein secretion and biogenesis of cell envelope components.

Effect of temperature on the stereoselectivity of phospholipase D toward glycerol in the transphosphatidylation of phosphatidylcholine to phosphatidylglycerol

In this study, the effect of temperature on the stereoselectivity of phospholipase D (PLD) toward the two primary hydroxyl groups of glycerol in the transphosphatidylation reaction of phosphatidylcholine to phosphatidylglycerol (PtdGro) was investigated. For this purpose, PLD from bacteria (Streptomyces septatus TH-2, S. halstedii subsp. scabies K6, and Actinomadura sp.) and cabbage were tested. At the reaction temperatures employed (0-60 degrees C), the proportions of the two PtdGro diastereomers, namely, 1,2-dioleoyl-sn-glycero-3-phospho-3'-sn-glycerol (R,R configuration) and 1 ,2-dioleoyl-sn-glycero-3-phospho-1'-sn-glycerol (R,S configuration), which were produced with PLD from Streptomyces TH-2 and Actinomadura sp., changed gradually from 50% R,R and 50% R,S at 50-60 degrees C to 70% R,R and 30% R,S at 0 degrees C. These alterations suggested that the stereoselectivity of the bacterial PLD toward the two primary hydroxyl groups of prochiral glycerol was significantly influenced by reaction temperature. PLD from Streptomyces K6 showed relatively little effect of temperature on stereoselectivity, giving 65-69% R,R in the temperature range of 60-10 degrees C examined. The plots of In ([R,R]/[R,S]) vs. 1/T gave good linear fits for these three bacterial PLD. No temperature effect was observed for cabbage PLD, which gave an almost equimolar mixture of the R,R and R,S diastereomers in the range from 0 to 40 degrees C. The temperature-dependent change in enantiomeric selectivity of the bacterial PLD promises potentially profitable commercial exploitation.

Phosphatidylglycerol and sulfoquinovosyldiacylglycerol: anionic membrane lipids and phosphate regulation

Photosynthetic membranes of organisms from cyanobacteria to seed plants are characterized by the neutral galactolipids and the anionic glycerolipids sulfoquinovosyldiacylglycerol and phosphatidylglycerol. Recent findings have brought new insights into the biosynthesis of the anionic membrane lipids, the evolutionary origin of the enzymes involved in this process, and the importance of phosphatidylglycerol and sulfoquinovosyldiacylgycerol in photosynthesis. Photosynthetic membranes require a defined level of anionic membrane lipids for proper function, and phosphatidylglycerol and sulfoquinovosyldiacylglycerol can substitute for each other to a certain extent. A defined level of phosphatidylglycerol is, however, indispensable for photoautotrophic growth. On the other hand, sulfoquinovosyldiacylglycerol plays a conditionally important role in enabling photosynthetic organisms to survive the phosphate-limiting conditions frequently encountered in natural habitats.

Modulation of phospholipase D-mediated phosphatidylglycerol formation by differentiating agents in primary mouse epidermal keratinocytes

The major component of the epidermis, keratinocytes, must continuously proliferate and differentiate to form the mechanical and water permeability barrier of the skin. Our previous data have suggested a potential role in these processes for phospholipase D (PLD), an enzyme that hydrolyzes phospholipids to generate phosphatidic acid. In the presence of primary alcohols, PLD also catalyzes a transphosphatidylation reaction to produce phosphatidylalcohols, and this characteristic has been exploited to monitor the activity of PLD in intact cells. In this report, PLD was demonstrated to utilize the physiological alcohol glycerol to form phosphatidylglycerol (PG) in vitro. In intact primary murine epidermal keratinocytes treated for 24 h with elevated extracellular Ca(2+) levels, but not 1,25-dihydroxyvitamin D(3), incubation with radioactive glycerol resulted in an increase in PLD-mediated radiolabeled PG production. This effect was dose-dependent and biphasic, with maximal PG formation detected after exposure to an intermediate (125 microM) Ca(2+) concentration. Furthermore, the biphasic nature of the response was due, in part, to a corresponding biphasic change in glycerol uptake. Finally, short-term treatment of keratinocytes with phorbol 12-myristate 13-acetate (PMA) failed to increase PG synthesis and inhibited glycerol uptake. Since (1) PMA is reported to activate PLD-1 to a greater extent than PLD-2, (2) 1,25-dihydroxyvitamin D(3) increases the expression/activity of PLD-1 in keratinocytes, and (3) PLD-2 is co-localized with a glycerol channel in keratinocyte membrane microdomains, we speculate that radiolabeled PG production from radioactive glycerol is a measure of PLD-2 activation in these cells. Our results also suggest that PLD-mediated PG synthesis may be regulated at the level of both PLD activity and alcohol substrate availability via changes in glycerol uptake.

The pgp1 mutant locus of Arabidopsis encodes a phosphatidylglycerolphosphate synthase with impaired activity

Phosphatidylglycerol is a ubiquitous phospholipid that is also present in the photosynthetic membranes of plants. Multiple independent lines of evidence suggest that this lipid plays a critical role for the proper function of photosynthetic membranes and cold acclimation. In eukaryotes, different subcellular compartments are competent for the biosynthesis of phosphatidylglycerol. Details on the plant-specific pathways in different organelles are scarce. Here, we describe a phosphatidylglycerol biosynthesis-deficient mutant of Arabidopsis, pgp1. The overall content of phosphatidylglycerol is reduced by 30%. This mutant carries a point mutation in the CDP-alcohol phosphotransferase motif of the phosphatidylglycerolphosphate synthase (EC 2.7.8.5) isoform encoded by a gene on chromosome 2. The mutant shows an 80% reduction in plastidic phosphatidylglycerolphosphate synthase activity consistent with the plastidic location of this particular isoform. Mutant plants are pale green, and their photosynthesis is impaired. This mutant provides a promising new tool to elucidate the biosynthesis and function of plastidic phosphatidylglycerol in seed plants.

A comparison of amniotic fluid fetal pulmonary phospholipids in normal and diabetic pregnancy

OBJECTIVE

Our purpose was to determine whether there are differences in the timing of the appearance of various amniotic fluid fetal pulmonary phospholipids in normal and diabetic pregnancy.

STUDY DESIGN

A case-control study of 295 subjects with diabetes and 590 control subjects was performed by use of gestational age-matched amniocentesis specimens analyzed for lecithin/sphingomyelin (L/S) ratio, phosphatidylinositol (PI), and phosphatidylglycerol (PG) composition. Diabetic subjects were stratified according to type of diabetes, degree of blood glucose control, and birth percentile of the neonate.

RESULTS

There was no difference in L/S ratios over gestational age by type of diabetes or quality of glycemic control. Women with preexisting diabetes had significantly higher PI levels at 33 to 35 weeks' gestation, which became similar to levels of control subjects after 36 weeks, whereas patients with gestational diabetes mellitus and control subjects had similar PI levels throughout. In diabetic subjects, the onset of production of PG was delayed from 35.9 +/- 1.1 weeks (controls) to 38.7 +/- 0.9 weeks (overt diabetics) and 37.3 +/- 1.0 weeks for gestational diabetes mellitus (P <.001). The delay in PG synthesis was not related to infant sex, level of maternal glucose control, or fetal macrosomia.

CONCLUSIONS

Fetal pulmonary maturation, as evidenced by the onset of PG production in the amniotic fluid, is delayed in diabetic pregnancy by 1 to 1.5 weeks. This delay appears to be associated with an early and sustained elevation in amniotic fluid PI levels at 32 to 34 weeks.

Malignant breast tumor phospholipid profiles using (31)P magnetic resonance

Biochemical markers improve the classification and staging of breast cancer and may refine management decisions if it can be shown that they correlate with accepted prognostic factors or patient outcome. Using phosphorus-31 magnetic resonance spectroscopy ((31)P MRS), we determined the phospholipid content of 43 malignant breast tumors, correlating the profiles with specific histopathologic and clinical features and hormone receptor status. Among the 14 phospholipids identified, the mean mole percentage of sphingomyelin, phosphatidylcholine, phosphatidylserine, phosphatidic acid, phosphatidylglycerol, and alkylacylphosphatidylcholine predicted cellular infiltration, infiltration type, elastosis, lymphatic invasion, perineural invasion, necrosis, and estrogen receptor positivity. (31)P MRS phospholipid profile data provide statistical correlations among histologic features and molecules known to play important roles in cellular communication, regulation, and processes unique to malignant tissues.

Coordinate packaging of newly synthesized phosphatidylcholine and phosphatidylglycerol in lamellar bodies in alveolar type II cells

Methylamine, a weak base, inhibits packaging of newly synthesized phosphatidylcholine (PC) in lamellar bodies in 20-22 h cultured alveolar type II cells, suggesting a role for acidic pH of lamellar bodies. In this study, we tested if (i) the packaging of PC is similarly regulated in freshly isolated type II cells and (ii) methylamine also inhibits the packaging of other surfactant phospholipids, particularly, phosphatidylglycerol (PG). The latter would suggest coordinated packaging so as to maintain the phospholipid composition of lung surfactant. During the short-term metabolic labeling experiments in freshly isolated type II cells, methylamine treatment decreased the incorporation of radioactive precursors into PC, disaturated PC (DSPC), and PG of lamellar bodies but not of the microsomes, when compared with controls. The calculated packaging (the percentage of microsomal lipid packaged in lamellar bodies) of each phospholipid was similarly decreased (approximately 50%) in methylamine-treated cells, suggesting coordinated packaging of surfactant phospholipids in lamellar bodies. Equilibrium-labeling studies with freshly isolated type II cells (as is routinely done for studies on surfactant secretion) +/- methylamine showed that in methylamine-treated cells, the secretion of PC and PG was decreased (possibly due to decreased packaging), but the phospholipid composition of released surfactant (measured by radioactivity distribution) was unchanged; and the PC content (measured by mass or radioactivity) of lamellar bodies was lower, but the PC composition (as percentage of total phospholipids) was unchanged when compared with control cells. We speculate that the newly synthesized surfactant phospholipids, PC, DSPC, and PG, are coordinately transported into lamellar bodies by a mechanism requiring the acidic pH, presumably, of lamellar bodies.

N-Acetylsphingosine stimulates phosphatidylglycerolphosphate synthase activity in H9c2 cardiac cells

Cardiolipin and phosphatidylglycerol biosynthesis were examined in H9c2 cells incubated with short-chain ceramides. Incubation of cells with N-acetylsphingosine or N-hexanoylsphingosine stimulated [1, 3-3H]glycerol incorporation into phosphatidylglycerol and cardiolipin, with N-acetylsphingosine having the greater effect. The mechanism for the ceramide-mediated stimulation of de novo phosphatidylglycerol and cardiolipin biosynthesis appeared to be an increase in the activity of phosphatidylglycerolphosphate synthase, the committed step of phosphatidylglycerol and cardiolipin biosynthesis. The presence of the potent protein phosphatase inhibitors calyculin A or okadaic acid attenuated the N-acetylsphingosine-mediated stimulation of phosphatidylglycerolphosphate synthase activity and of phosphatidylglycerol and cardiolipin biosynthesis, indicating the involvement of a ceramide-activated protein phosphatase(s). The presence of 8-(4-chlorophenylthio)-cAMP (CPT-cAMP) stimulated enzyme activity and [1,3-3H]glycerol incorporation into phosphatidylglycerol and cardiolipin. The effects of CPT-cAMP and N-acetylsphingosine on phosphatidylglycerol and cardiolipin biosynthesis and on phosphatidylglycerolphosphate synthase activity were additive. Phosphatidylglycerol biosynthesis from sn-[14C]glycerol 3-phosphate in permeabilized H9c2 cells was stimulated by preincubation with N-acetylsphingosine, and this was attenuated by okadaic acid. N-Acetylsphingosine treatment of cells elevated mitochondrial phospholipase A2 activity. Since the pool sizes of phosphatidylglycerol and cardiolipin were unaltered in these cells, the observed increase in phosphatidylglycerolphosphate synthase activity may be a compensatory mechanism for the N-acetylsphingosine-mediated elevation of mitochondrial phospholipase A2 activity. Finally, addition of tumour necrosis factor alpha to H9c2 cells resulted in an elevation of both phosphatidylglycerolphosphate synthase and phospholipase A2 activities. The results suggest that phosphatidylglycerol and cardiolipin metabolism in H9c2 cells may be regulated by intracellular ceramide signalling.

Isolation of a chinese hamster ovary (CHO) cDNA encoding phosphatidylglycerophosphate (PGP) synthase, expression of which corrects the mitochondrial abnormalities of a PGP synthase-defective mutant of CHO-K1 cells

Phosphatidylglycerophosphate (PGP) synthase catalyzes the first step in the cardiolipin (CL) branch of phospholipid biosynthesis in mammalian cells. In this study, we isolated a Chinese hamster ovary (CHO) cDNA encoding a putative protein similar in sequence to the yeast PGS1 gene product, PGP synthase. The gene for the isolated CHO cDNA was named PGS1. Expression of the CHO PGS1 cDNA in CHO-K1 cells and production of a recombinant CHO PGS1 protein with a N-terminal extension in Escherichia coli resulted in 15-fold and 90-fold increases of PGP synthase specific activity, respectively, establishing that CHO PGS1 encodes PGP synthase. A PGP synthase-defective CHO mutant, PGS-S, isolated previously (Ohtsuka, T., Nishijima, M., and Akamatsu, Y. (1993) J. Biol. Chem. 268, 22908-22913) exhibits striking reductions in biosynthetic rate and cellular content of phosphatidylglycerol (PG) and CL and shows mitochondrial morphological and functional abnormalities. The CHO PGS-S mutant transfected with the CHO PGS1 cDNA exhibited 620-fold and 7-fold higher PGP synthase activity than mutant PGS-S and wild type CHO-K1 cells, respectively, and had a normal cellular content and rate of biosynthesis of PG and CL. In contrast to mutant PGS-S, the transfectant had morphologically normal mitochondria. When the transfectant and mutant PGS-S cells were cultivated in a glucose-depleted medium, in which cellular energy production mainly depends on mitochondrial function, the transformant but not mutant PGS-S was capable of growth. These results demonstrated that the morphological and functional defects displayed by the PGS-S mutant are due directly to the reduced ability to make normal levels of PG and/or CL.

The interfacial pressure is an important parameter for the rate of phospholipase D catalyzed reactions in emulsion systems

Phospholipase D (PLD) is widely used for the transformation of phospholipids, which is preferably performed in aqueous-organic emulsion systems. The influence of the organic solvent on the reaction rates has been studied on the hydrolysis of phosphatidylcholine (PC) and its transesterification with glycerol by two types of PLD (cabbage and Streptomyces sp.). The initial rates determined by quantitative HPTLC show great differences in dependence on the solvent used with a similar tendency for both reactions and both PLDs. Since the polymorphism of the PC aggregates was assumed to be responsible for these effects, the critical concentration of micelle formation, the size of the aggregates, the water content of the organic phase, and the interfacial tension were determined in the different reaction systems. As result the interfacial pressure in the reaction systems influencing the package density of the PC aggregates is suggested to regulate the enzymatic activity.

Effect of epidermal growth factor on enzymes of phospholipid biosynthesis in lung and liver of fetal rat in vivo and in vitro

Epidermal growth factor (EGF), a mitogenic polypeptide that binds to cell surface receptors, is an important regulator of cell differentiation and fetal lung surfactant synthesis, and may be used as a potential novel therapeutic agent in prematurity. Nevertheless, the distinct role in lung development and its mechanisms of action are not well understood. We investigated in vivo the systemic effect of intrafetally administered EGF (200 ng/g fetal body weight) and maternally administered dexamethasone (DEXA; 0.2 and 2.0mg/kg maternal body weight) on the activity of important enzymes of the phospholipid synthesis in the fetal rat lung and liver: choline kinase (EC 2.7.1.32), cholinephosphate cytidyltransferase (EC 2.7.7.15), choline phosphotransferase (EC 2.7.8.2), lysolecithin acyltransferase (EC 2.3.1.23) and glycerolphosphate phosphatidyltransferase (EC 2.7.8.5). Additionally, in vivo and in vitro effects of DEXA on EGF receptor synthesis, and the effects of EGF on protein content and morphogenesis of the fetal rat lung organoid culture, were evaluated. Whereas DEXA induced the activity of all investigated enzymes of phospholipid synthesis and increased EGF receptor synthesis, EGF has no effects on the enzymes, either in vivo or in vitro. EGF enhanced protein synthesis and morphogenesis in vitro. With respect to our data and the literature, we hypothesize that DEXA and EGF may act on different cellular sides. Whereas glucocorticoids induce surfactant phospholipid synthesis, EGF should be more involved in cell proliferation and morphogenesis.

The effect of growth temperature on the phospholipid and fatty acyl compositions of non-proteolytic Clostridium botulinum

A non-proteolytic strain of Clostridium botulinum (NCIB 4270) was found to have a complex lipid composition, comprising five major phosphorus-containing lipids: phosphatidylethanolamine (PE), phosphatidylglycerol (PG), diphosphatidylglycerol (DPG), phosphatidylserine (PS) and a glycophospholipid of unknown structure (GPL), in order of abundance. Changing the growth temperature did not alter the lipid composition either qualitatively or quantitatively. The main fatty acyl components of the lipids are 14:0, 16:0 and 16:1. When the growth temperature was lowered from 37 to 8 degrees C, there was an increase in 14:0 from 16.4 to 37.5%, an increase in 16:1 from 10.5 to 22.5%, and a decrease in the proportion of 16:0 from 40.3 to 19.1%. There was also a decrease in the proportion of cyclopropane fatty acids (15:0cyc and 17:0cyc) from 7.3 to 0.5%, and in the equivalent chain length of the total fatty acids from 15.9 to 15.3 as the temperature was lowered. The same temperature-dependent changes occurred in the five major lipid classes examined. Despite reports of the presence of plasmalogenic forms of phospholipids (i.e. those lipids which have the acyl chain in the sn-1 position replaced by an alk-1-enyl group) in some Clostridium spp., none were detected in C. botulinum NCIB 4270 using either commercially available spray reagents or by gas-liquid chromatographic analysis of the products or acid methanolysis of total lipid extracts. It is concluded that non-proteolytic C. botulinum lacks plasmalogens, typical of other clostridia, in its membranes and instead modulates its fatty acid composition in response to temperature changes in a manner that is typical of other (non-clostridial) bacteria.

Alteration of fatty acid composition in a pgsA3 mutant of Escherichia coli

We examined the fatty acid composition in an Escherichia coli pgsA3 mutant lacking the potential to synthesize phosphatidylglycerolphosphate, a precursor of phosphatidylglycerol. The contents of C18:1cis-9 (oleic acid) and C18:1cis-11 (cis-vaccenic acid) in the total phospholipids extracted from the pgsA3 mutant growing at 37 degrees C were higher and that of C14:0 was lower than the wild type cells, resulting in a higher level of unsaturation of fatty acids (ratio of unsaturated fatty acids to saturated ones) in the mutant. The higher level of the unsaturated fatty acids in the pgsA3 mutant was more obvious in cardiolipin than in phosphatidylethanolamine. On the other hand, at 28 degrees C, at which the pgsA3 mutant shows limited cell growth, the content of unsaturated fatty acids in cardiolipin decreased in the pgsA3 mutant compared with the wild type. We consider that the pgsA3 mutant maintains cellular homeostasis by altering the level of unsaturated fatty acids in cardiolipin, and the mechanism is influenced by temperature.

Regulation of cardiolipin biosynthesis in H9c2 cardiac myoblasts by cytidine 5'-triphosphate

The regulation of cardiolipin biosynthesis by CTP in H9c2 cardiac myoblasts was investigated. H9c2 cells were incubated in the presence of cyclopentenylcytosine which is converted to cyclopentenylcytosine-triphosphate, a potent and specific inhibitor of CTP synthetase. Incubation of cells for 12 h with cyclopentenylcytosine reduced the cellular pool size of CTP to less than 10% of control cells but did not influence the pool size of other nucleotides. The de novo biosynthesis of phosphatidylcholine from [methyl-3H]choline, phosphatidylethanolamine from [1-3H]ethanolamine, and biosynthesis of all glycerol containing phospholipids from [U-14C]glycerol or [1,3-3H]glycerol were reduced approximately 50% after preincubation of the cells with cyclopentenylcytosine. In contrast, radioactive glycerol accumulated in phosphatidic acid, diacylglycerol, and triacylglycerol in cyclopentenylcytosine-treated cells compared with controls suggesting a re-routing of phospholipid biosynthesis away from CTP utilizing reactions toward neutral lipid synthesis. The de novo biosynthesis of all phospholipids was restored to control levels by addition of cytidine to the medium which elevated CTP levels. Cyclopentenylcytosine did not affect the in vitro enzyme activities involved in cardiolipin biosynthesis in these cells. In addition, the resynthesis of cardiolipin and most phospholipids from [1-14C]linoleic acid was not affected by cyclopentenylcytosine. Our findings indicate that the cellular CTP level may regulate cardiolipin biosynthesis in H9c2 cardiac myoblasts and support the notion that the cellular CTP level may be a universal signal/switch for all phospholipid biosynthesis in eukaryotic cells.

Growth phenotypes of Escherichia coli carrying a mutation of acidic phospholipid synthesis

We identified novel phenotypes of a pgsA3 mutant lacking the potential to synthesize phosphatidylglycerophosphate, a precursor of phosphatidylglycerol. The first phenotype is limited cell growth at a high temperature, under the condition of low salt. The phenotype was co-transduced with a phenotype lacking the potential to synthesize phosphatidylglycerol in a P1 transduction experiment, and was restored by transformation with a plasmid containing a wild type pgsA gene. The second phenotype of the pgsA3 mutant was resistant to growth in the presence of a low concentration of kanamycin (4 micrograms/ml). P1 transduction and transformation with the plasmid containing the wild-type pgsA gene revealed that the pgsA3 mutation was also responsible for the second phenotype.

Isolation and expression of the Rhodobacter sphaeroides gene (pgsA) encoding phosphatidylglycerophosphate synthase

The Rhodobacter sphaeroides pgsA gene (pgsARs), encoding phosphatidylglycerophosphate synthase (PgsARs), was cloned, sequenced, and expressed in both R. sphaeroides and Escherichia coli. As in E. coli, pgsARs is located immediately downstream of the uvrC gene. Comparison of the deduced amino acid sequences revealed 41% identity and 69% similarity to the pgsA gene of E. coli, with similar homology to the products of the putative pgsA genes of several other bacteria. Comparison of the amino acid sequences of a number of enzymes involved in CDP-diacylglycerol-dependent phosphatidyltransfer identified a highly conserved region also found in PgsARs. The pgsARs gene carried on multicopy plasmids was expressed in R. sphaeroides under the direction of its own promoter, the R. sphaeroides rrnB promoter, and the E. coli lac promoter, and this resulted in significant overproduction of PgsARs activity. Expression of PgsARs activity in E. coli occurred only with the E. coli lac promoter. PgsARs could functionally replace the E. coli enzyme in both a point mutant and a null mutant of E. coli pgsA. Overexpression of PgsARs in either E. coli or R. sphaeroides did not have dramatic effects on the phospholipid composition of the cells, suggesting regulation of the activity of this enzyme in both organisms.

A regulatory mechanism for the balanced synthesis of membrane phospholipid species in Escherichia coli

The mechanism that assures the balanced synthesis of zwitterionic (phosphatidylethanolamine) and acidic phospholipids (phosphatidylglycerol and cardiolipin) in Escherichia coli has been examined by genetically manipulating the two enzymes at the biosynthetic branch point, i.e., phosphatidylglycerophosphate synthase, encoded by pgsA, and phosphatidylserine synthase, encoded by pssA. A mutant in which the most part of the pssA gene was replaced with a drug resistance gene lacked phosphatidylserine synthase and phosphatidylethanolamine and required divalent metal ions for growth, as did a previously reported insertion-inactivated pssA mutant. When this mutant harbored a plasmid containing a Bacillus subtilis gene that encodes membrane-bound phosphatidylserine synthase, the phosphatidylethanolamine content was dependent on its activity, in contrast to that with the soluble E. coli counterpart. A defective mutation, pgsA3, caused reductions not only in acidic-phospholipid synthesis but also in phosphatidylethanolamine synthesis, despite the normal level of phosphatidylserine synthase activity. These results, together with previous observations, indicate that phosphatidylserine synthesis requires the membrane-associated form of phosphatidylserine synthase, which is related to the membrane-levels of acidic phospholipids, thus yielding balanced compositions of zwitterionic and acidic phospholipids.

Eukaryotic phospholipid biosynthesis

The current status of the biochemistry of phospholipid biosynthesis is presented. The review focuses on the identification and characterization of molecular tools such as purified enzymes and cloned genes and cDNAs for those enzymes. The enzymes discussed are those involved in the biosynthesis of the major phospholipid classes, namely, phosphatidate, phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine, sphingomyelin, phosphatidylinositol and its phosphorylated derivatives, and cardiolipin. The review centers on the pathways in mammals and yeast. Novel genetic approaches used to delineate pathways and clone cDNAs are discussed. The regulatory roles played by some of the enzymes involved in controlling the biosynthetic pathways are presented.

Thapsigargin selectively stimulates synthesis of phosphatidylglycerol in N1E-115 neuroblastoma cells and phosphatidylinositol in C6 glioma cells

Phospholipid metabolism was studied in N1E-115 neuroblastoma and C6 glioma cells exposed to thapsigargin, a selective inhibitor of endoplasmic reticulum Ca(2+)-ATPase that raises the cytosolic free Ca2+ concentration [Ca2+]i. Thapsigargin caused only a transient increase of [Ca2+]i (< 1 min) in N1E-115 cells similar in magnitude and duration to agonist-induced calcium release mediated by inositol trisphosphate. Sustained elevation of [Ca2+]i due to influx of extracellular calcium, as occurs in most other cell lines including C6 cells, did not occur in N1E-115 cells. Increased uptake of inorganic phosphate (Pi) associated calcium influx was observed in C6 but not in N1E-115 cells. Thapsigargin affected phospholipid synthesis in both cell lines, most likely by inhibiting phosphatidic acid phosphohydrolase as indicated by diversion of [3H]oleic acid incorporation from triacylglycerol to phospholipid synthesis and stimulation of [32P]Pi incorporation into anionic phospholipids at the expense of phosphatidylcholine synthesis. The response to increased phosphatidate/phosphatidyl-CMP availability was cell specific. Thapsigargin (> 100 nM) selectively stimulated phosphatidylglycerol synthesis 20-30-fold in N1E-115 neuroblastoma cells while phosphatidylinositol synthesis was increased < 2-fold. In contrast, phosphatidylglycerol was not affected in C6 glioma cells and phosphatidylinositol synthesis was stimulated 8-fold by thapsigargin (> 1 microM). Agonist-stimulated calcium release did not increase phosphatidylglycerol synthesis in N1E-115 cells. Thapsigargin-stimulated phosphatidylglycerol synthesis and agonist-stimulated phosphatidylinositol synthesis could occur at the same time. Similar results were obtained with TMB-8, an inhibitor of intracellular Ca2+ release that decreases diacylglycerol utilization by blocking choline uptake and phosphatidylcholine synthesis without affecting resting [Ca2+]i. Thus [Ca2+]i does not directly mediate the effects of thapsigargin, TMB-8 or agonist stimulation on anionic phospholipid metabolism. These additional effects may limit the use of thapsigargin to assess Ca(2+)-dependence of phospholipid metabolism associated with Ca(2+)-mediated signal transduction.

Biochemical studies of three Saccharomyces cerevisiae acyl-CoA synthetases, Faa1p, Faa2p, and Faa3p

The efficiency and specificity of protein N-myristoylation appear to be influenced by the availability of myristoyl-CoA and other potential acyl-CoA substrates of myristoyl-CoA:protein N-myristoyltransferase. Recent studies have revealed that Saccharomyces cerevisiae contains at least three acyl-CoA synthetase genes (FAA for fatty acid activation). We have expressed Faa1p, Faa2p, and Faa3p in a strain of Escherichia coli that lacks its own endogenous acyl-CoA synthetase (FadD). Each S. cerevisiae acyl-CoA synthetase contained a carboxyl-terminal His tag so that it could be purified to homogeneity in a single step using nickel chelate affinity chromatography. In vitro assays of C3:0-C24:0 fatty acids indicate that Faa1p prefers C12:0-C16:0, with myristic and pentadecanoic acid (C15:0) having the highest activities. Faa2p can accommodate a wider range of acyl chain lengths: C9:0-C13:0 are preferred and have equivalent activities, although C7:0-C17:0 fatty acids are tolerated as substrates with no greater than a 2-fold variation in specific activity. The myristoyl-CoA synthetase activities of Faa1p and Faa2p are 2 orders of magnitude greater than that of Faa3p in vitro. Faa3p has a preference for C16 and C18 fatty acids with a cis-double bond at C-9-C-10. The temperature optimum for Faa1p is 30 degrees C, while Faa2p and Faa3p have the greatest activities at 25 degrees C. These in vitro observations were confirmed using two in vivo assays: (i) measurement of the ability of each S. cerevisiae acyl-CoA synthetase to direct the incorporation of exogenously derived tritiated myristate, palmitate, or oleate into cellular phospholipids produced in a fadD- strain of E. coli during exponential growth at 24 or 37 degrees C and (ii) measurement of the incorporation of [3H]myristate into a yeast N-myristoylprotein coexpressed with Nmt1p and Faa1p, Faa2p, or Faa3p in the fadD- strain.

beta-Adrenergic priming of rats in vivo modulates the effect of beta-agonist in vitro on surfactant phospholipid metabolism of isolated lungs

To evaluate the effects of multiple beta-adrenergic stimulations on pulmonary surfactant phospholipids, perfused lungs from beta-adrenergic primed and non-primed rats were challenged with the beta-agonist terbutaline in vitro. Cell-free lung lavage, lavagable alveolar cells and lung tissue were analysed for phospholipid content and incorporation of precursors. In lung lavage, terbutaline in vitro doubled the incorporation of 14C-choline and 3H-palmitate into total phosphatidylcholine (PC) and of 3H-palmitate into phosphatidylglycerol (PG). beta-adrenergic priming in vivo prior to terbutaline in vitro lowered the increase of precursor incorporation. For lavagable cells, terbutaline in vitro increased the incorporation of 3H-palmitate into PC. Priming in vivo reduced this effect and diminished the specific 3H-choline incorporation into lavagable cell PC below control level. For lung tissue, priming increased the amounts of PC and disaturated PC (DSPC) whereas terbutaline in vitro decreased DSPC in both primed and non-primed lungs. Terbutaline in vitro slightly increased the incorporation of 14C-choline and 3H-palmitate into PC and DSPC in non-primed but not in primed lungs. beta-adrenergic blockade by ICI 118.551 prevented all effects but generally increased 3H-palmitate incorporation into the phospholipids and, in lavagable cells, the amount of PC. We conclude that long-term beta-adrenergic treatment may alter the metabolism of pulmonary surfactant phospholipids by increasing tissue PC and DSPC and by decreasing the secretion of newly-synthesized PC.

Effect of pentoxifylline on the inhibition of surfactant synthesis induced by TNF-alpha in human type II pneumocytes

Tumor necrosis factor alpha (TNF-alpha) seems to play an important role in the pathogenesis of the adult respiratory distress syndrome (ARDS). This study was designed to determine the effect of TNF-alpha and pentoxifylline (PTXF) on surfactant synthesis by isolated human type II pneumocytes. In order to isolate the pneumocytes, lungs obtained from both previously healthy multiple organ donors (n = 11) and patients who underwent surgical excision for lung cancer (n = 8) were used. Surfactant synthesis was measured by the incorporation of labeled glucose into the two most important phospholipid components of surfactant: phosphatidylcholine (PC) and phosphatidylglycerol (PGL). The pneumocytes of the donor group showed a greater degree of PC synthesis than those from the cancer group (3.44 +/- 0.19 versus 2.15 +/- 01.5 pmol/micrograms protein, p < 0.001). The synthesis of PC by pneumocytes in both the donor (1.13 +/- 0.19 versus 3.44 +/- 0.19 pmol/micrograms protein, p < 0.01) and cancer (0.99 +/- 0.11 versus 2.15 +/- 0.15 pmol/micrograms protein, p < 0.01) groups was decreased by TNF-alpha (100 ng/ml). This effect was blocked by PTXF (100 micrograms/ml), a substance that also increased PC production in the control-group pneumocytes from cancer patients, the final PC levels being similar to those of the donors in the absence of TNF-alpha. These results suggest that one of the mechanisms of TNF-alpha participation in the pathophysiology of ARDS is inhibition of surfactant synthesis, and support the hypothesis of in vivo production of TNF-alpha in lung-cancer patients, with subsequent chronic exposure of the lung epithelial cells to this cytokine.(ABSTRACT TRUNCATED AT 250 WORDS)

A somatic cell mutant defective in phosphatidylglycerophosphate synthase, with impaired phosphatidylglycerol and cardiolipin biosynthesis

Phosphatidylglycerophosphate (PGP) synthase catalyzes a reaction involved in the synthesis of phosphatidylglycerol (PG), which serves as a metabolic precursor for cardiolipin (CL), found primarily in the mitochondrial membranes of eukaryotic cells. We isolated a Chinese hamster ovary cell mutant (designated PGS-S) with a specific lesion in PGP synthase by using an in situ enzymatic assay for the enzyme. This mutant was obtained by introducing a second mutation into mutant PGS-P that had been generated by first-step mutagenesis. The PGP synthase activities in cell extracts of mutant PGS-S grown at 33 and 40 degrees C were 14 and 1% of those in the wild type cells, respectively; in addition, PGP synthase in cell extracts of mutant PGS-S exhibited higher sensitivity to heat than that of the wild type. Mutant PGS-S also showed a temperature-dependent defect in the synthesis of PG and CL in vivo, together with temperature sensitivity for cell growth. A temperature-resistant revertant of mutant PGS-S simultaneously restored PGP synthase activity and the ability to synthesize PG and CL in vivo to nearly the same levels as those of mutant PGS-P. These results constitute genetic evidence that PGP synthase is responsible for PG synthesis and is essential for cell growth.

Requirement of phosphatidylglycerol for flagellation of Escherichia coli

We report that phosphatidylglycerol is required for flagellation of Escherichia coli. Cells carrying the pgsA3 mutation did not form swarm rings in semisolid agar. P1 transduction experiments revealed that the potential for phosphatidylglycerol synthesis and for the formation of swarm rings was co-transducible. The pgsA3 mutant transformed with the wild type pgsA+ gene cloned into the R-plasmid vector had the potential for both phosphatidylglycerol synthesis and cell motility. Electromicroscopic and SDS-PAGE analyses showed that the pgsA3 mutation causes the lack of flagellation.

Biosynthesis and characterization of phosphatidylglycerophosphoglycerol, a possible intermediate in lipoteichoic acid biosynthesis in Streptococcus sanguis

A membrane enzyme preparation from Streptococcus sanguis was shown to convert sn-[14C]glycerol 3-phosphate and CDP-diacylglycerol (or deoxyCDP-diacylglycerol) into a series of progressively higher-molecular-weight [14C]oligophosphoglycerophospholipids in vitro. The first oligophosphoglycerophospholipid to accumulate (termed lipid-1) was purified to homogeneity; chemical analysis, gas-liquid chromatography and chemical degradation studies indicated the most likely structure to be phosphatidylglycerophosphoglycerol (PGpG). PGpG is formed directly from two molecules of phosphatidylglycerol (PG), one molecule of PG serving as a sn-glycerol 1-phosphate (pG) donor and the second serving as the pG acceptor, with co-production of diacylglycerol. These oligophosphoglycerophospholipids may be intermediates in the biosynthesis of lipoteichoic acids.

The phosphonic acid analog of phosphatidylglycerol phosphate: influence on Escherichia coli growth and physiology

At 20 microM, rac-3,4-dihydroxybutyl-1-phosphonate (DBP) has only a slight bacteriostatic effect on Escherichia coli. However, cells lose viability when the medium also contains either 20 mM magnesium or calcium ions. Magnesium ions stimulate the incorporation of DBP into (1,2-diacyl)-sn-glycerol-D-4'-phosphoryloxy-3'-hydroxybutyl-1'-pho sphonate, the phosphonate analog of phosphatidylglycerol phosphate. Much higher DBP concentrations are needed to block the growth of a pgsA3 mutant than to block the growth of an isogenic wild-type strain. The DBP-treated pgsA mutant also has a much higher survival rate when stored in the cold than does the DBP-treated wild-type strain. Furthermore, the pgsA3 mutant grows normally in the presence of DBP and magnesium ions. Treatment with DBP and magnesium ions does not appear to disrupt the cell's inner or outer membranes. However, it does block macromolecular and phosphoglyceride synthesis. A combination of 20 microM rac-DBP and 0.5 mM spermidine or 0.125 mM spermine is bacteriostatic. These studies indicate that the PGP analog contributes to DBP's bacteriostatic effect when the growth medium contains low concentrations of magnesium or calcium ions and is responsible for its bactericidal effect when the medium contains high concentrations of these ions.

Calcium-independent effects of TMB-8. Modification of phospholipid metabolism in neuroblastoma cells by inhibition of choline uptake

TMB-8 [8-(NN-diethylamino)-octyl-3,4,5-trimethoxybenzoate] blocks agonist-stimulated release of Ca2+ from intracellular sites in many cell lines and is often used to distinguish between dependence on extracellular and intracellular Ca2+. In N1E-115 neuroblastoma cells, TMB-8 did not alter the resting cytosolic Ca2+ concentration in unstimulated cells, yet phospholipid metabolism was greatly affected. At concentrations of TMB-8 (25-150 microM) that inhibit Ca2+ release, phosphatidylcholine formation was inhibited, whereas synthesis of phosphatidylinositol, phosphatidylglycerol and phosphatidylserine was stimulated. Unlike other cationic amphipathic compounds, TMB-8 did not inhibit phosphatidate phosphatase or enzymes in the pathway from choline to phosphatidylcholine. Choline transport was the major site of action. TMB-8 was a competitive inhibitor (Ki = 10 microM) of low-affinity (Kt = 20 microM) choline transport. When added at the same time as labelled precursor, TMB-8 also decreased cellular uptake of phosphate and inositol, but not that of ethanolamine or serine. In prelabelled cells, continued uptake and incorporation of phosphate and inositol were not affected. Under these conditions phosphatidylinositol synthesis was increased 2-fold and, like the effect on phosphatidylcholine, reached a plateau at 100 microM-TMB-8. Phosphatidylglycerol synthesis increased linearly with TMB-8 concentration to 40-fold stimulation at 150 microM, suggesting a selective effect on synthesis of phosphatidylglycerol from CDP-diacylglycerol. Phosphatidylserine synthesis was also increased up to 3-fold. These Ca(2+)-independent effects limit the use of TMB-8 in studies of cell signalling that involve stimulated phosphatidylinositol and phosphatidylcholine metabolism.

Surfactant phospholipids: synthesis and storage

Pulmonary surfactant, a complex consisting of 90% lipids and 10% specific proteins, lines the alveoli of the lung and prevents alveolar collapse and transudation by lowering the surface tension at the air-liquid interface. Dipalmitoylphosphatidylcholine constitutes approximately 50% of the surfactant lipids and is primarily responsible for the surface tension-lowering property of the surfactant mixture. This phospholipid, together with the other surfactant phospholipids, is produced at the endoplasmic reticulum of the alveolar type II epithelial cells. The characteristic lamellar bodies in these cells serve as storage depot for the surfactant before this is secreted onto the alveolar surface. This article reviews the pathways via which the surfactant lipids are synthesized, our current knowledge of the regulation of these pathways, and what is known about intracellular traffic of phospholipids from their site of synthesis to the lamellar bodies.

Biosynthesis of the unique trans-delta 3-hexadecenoic acid component of chloroplast phosphatidylglycerol: evidence concerning its site and mechanism of formation

As in most higher plants, chloroplast membranes of the green alga Dunaliella salina contain phosphatidylglycerol (PG) that is rich in trans-delta 3-hexadecenoic acid (16:1t), a fatty acid found nowhere else in the cell. After labeling D. salina with exogenous [3H]myristic acid [( 3H]14:0), the cis-unsaturated fatty acids of monogalactosyldiacylglycerol and sulfoquinovosyldiacylglycerol as well as PG had higher specific radioactivities in chloroplast envelopes than in thylakoids. In contrast, 16:1t was very slow to become radioactive, and its specific radioactivity was several times higher in isolated thylakoids than in envelopes after brief (3-20 min) labeling with [3H]14:0. Analysis of individual PG molecular species revealed that the fatty acid paired with 16:1t was also labeled slowly. Thus linoleate (18:2) released from a 16:1t-containing PG had a 350-fold (at 3 min) to 20-fold (at 60 min) lower specific radioactivity than did 18:2 from a palmitate (16:0)-containing PG. The findings suggest that the substrates for trans-desaturation are 16:0-containing PG molecular species which are readily labeled from [3H]14:0 in the envelope but are diluted by the large pool of thylakoid PG before penetrating to the desaturation site. By examining the labeling patterns of individual PG molecular species classes, it was concluded that D. salina 16:1t is formed from 16:0 linked to 18:2/16:0 PG and 18:3/16:0 PG by a trans-desaturase located within the inner recesses of the thylakoid compartment.

Phosphatidylglycerol acetal of plasmenylethanolamine as an intermediate in ether lipid formation in Clostridium butyricum

The formation and turnover of the recently discovered phosphatidylglycerol acetal of plasmenylethanolamine was investigated in Clostridium butyricum. Incorporation of phosphate into the phospholipids was studied by using [32P]orthophosphate in pulse and pulse-chase experiments in growing cells. Among the ethanolamine-containing lipids, the diacyl form of phosphatidylethanolamine was labeled most rapidly, followed by the phosphatidylglycerol acetal of plasmenylethanolamine and plasmenylethanolamine. The glycerol acetal of plasmenylethanolamine was labeled most slowly. There was rapid turnover of approximately one half of the newly labeled phosphatidylethanolamine pool. Since the kinetics of labeling of the small pool of phosphatidylglycerol acetal of plasmenylethanolamine and the larger pool of plasmenylethanolamine were similar during the early time courses of pulse and pulse-chase experiments, the results argue against the derivation of phosphatidylglycerol acetal of plasmenylethanolamine from plasmenylethanolamine. The results are consistent with the derivation of glycerol acetal of plasmenylethanolamine from either phosphatidylglycerol acetal of plasmenylethanolamine or plasmenylethanolamine.

Biosynthesis of phosphatidylglycerol and phosphatidylglycerolphosphate in submitochondrial membranes isolated from guinea pig liver is absolutely dependent on CDP-diglycerides imported from microsomal membranes

The biosynthesis of radioactively labelled phosphatidylglycerol via phosphatidylglycerophosphate in outer and inner mitochondrial membranes isolated from guinea pig liver was found to depend absolutely on CDP-diglycerides, which could not be biosynthesized in these membranes. The requirement for CDP-diglycerides in the biosynthesis of labelled phosphatidylglycerol could be fulfilled by the transfer of biosynthesized [3H]CDP-diglycerides from the microsomal membranes to the outer and inner mitochondrial membranes.

Comparison of the biosynthesis and composition of polyglycerophosphatides and phosphatidylinositols in mitochondria and microsomes isolated from neonatal and adult rat heart and liver

The level of biosynthesis and the composition of polyglycerophosphatides (phosphatidylglycerol, phosphatidyglycerolphosphate, and diphosphatidylglycerol or cardiolipin) and phosphatidylinositols were examined in mitochondria and microsomes, respectively, isolated from neonatal and adult rat heart and liver. Biosynthesis of [3H]polyglycerophosphatides [( 3H]phosphatidylglycerol and [3H]phosphatidylglycerolphosphate) was 4.5 times higher in neonatal than in adult heart mitochondria, whereas in the respective liver mitochondria this synthesis was only 15% higher in neonatal mitochondria. The biosynthesis of [3H]phosphatidylinositol was twice as high in neonatal as in adult heart microsomes, but very similar in the respective liver microsomes. The major biosynthesized polyglycerophosphatide was [3H]phosphatidylglycerol. The accumulation of [3H]phosphatidylglycerolphosphate depended on the origin of the mitochondria. Under our experimental conditions [3H]phosphatidylinositol was the only synthesized phosphoinositide in all microsomes. The biosynthesis of cardiolipin depended on the origin of the mitochondria and was highest in adult rat liver mitochondria and lowest in adult heart mitochondria. In all cases the biosynthesized [14C,3H] cardiolipin from [14C]phosphatidylglycerol and [3H]CDP-diglycerides had a ratio of 14C/3H around unity. The biosynthesis of [3H]CDP-diglycerides, the key precursor for the biosynthesis of phosphatidylglycerol, phosphatidylinositol, and cardiolipin, was 30% higher in neonatal than in adult heart microsomes and very similar in the respective liver microsomes. The subcellular localization of the enzymes required for the biosynthesis of the lipids and liponucleotides examined was found to be the same in membranes isolated from neonatal and adult rat heart and liver.

Formation of acylphosphatidylglycerol by a lysosomal phosphatidylcholine:bis(monoacylglycero)phosphate acyl transferase

A delipidated soluble fraction prepared from a mitochondrial-lysosomal fraction of rabbit alveolar macrophages that catalyzes transacylation of lysophosphatidylglycerol to form bis(monoacylglycero)phosphate was also found to transfer oleic acid from [14C]dioleoyl phosphatidylcholine to form acylphosphatidylglycerol. The reaction was dependent on the presence of bis(monoacylglycero)phosphate and was maximal at a concentration of 44 microM when the ratio of fatty acid transferred to fatty acid released was 0.28. Addition of phosphatidylglycerol had only a small effect. Homogenates of rat liver also catalyzed the reaction and after subcellular fractionation the activity was localized to lysosomes. The lysosomal activity was solubilized by delipidation with butanol to give a preparation with a specific activity 2462 times that of the homogenate. Optimal activity of soluble preparations from both macrophages and liver was at pH 4.5, with little activity above 6.0. Release of free fatty acid was also stimulated under conditions of optimal acyl transfer. Both acyl transfer and release of fatty acid were inhibited by Ca2+, detergents, chlorpromazine, lysophosphatidylcholine, and oleic acid. When there was disproportional inhibition, acyl transfer was always more affected. These results suggest that sequential acylation of lysophosphatidylglycerol to form bis(monoacylglycero)phosphate and then acylphosphatidylglycerol constitute a mechanism in the lysosome for the transport and partition of fatty acids released by the lysosomal phospholipases.

Alteration of the phospholipid composition of Escherichia coli through genetic manipulation

In order to study the function of individual phospholipids, we have constructed a strain of Escherichia coli in which the ratio of phosphatidylethanolamine to phosphatidylglycerol plus cardiolipin can be regulated. In this strain (HDL1001) the normal expression of the phosphatidylglycerophosphate synthase does not occur due to the presence of the pgsA30 allele (Heacock, P. N., and Dowhan, W. (1987) J. Biol. Chem. 262, 13044-13049). A second chromosomal copy of the pgsA gene is fused to the lacOP region in single copy within the lac operon. Strain HDL1001 is absolutely dependent for growth on an inducer of the lac operon. In addition, the level of the pgsA gene product, the content of the two major acidic phospholipids, and the growth rate are dependent on the level of inducer in the growth medium. Cells remain viable in the absence of inducer as evidenced by a rapid return to normal growth after the readdition of inducer. The growth rate and phospholipid composition are affected only after the level of phosphatidylglycerophosphate synthase drops below about 15% of normal levels; both phosphatidic acid and (d)CDP-diacylglycerol also begin to increase to significant levels. At the point of cell arrest the level of the major acidic phospholipids is reduced by about 90% of wild type levels.