Modification of the Dittmer-Lester reagent for the detection of phospholipid derivatives on thin-layer chromatograms

Characterization of recombinant murine GDE4 and GDE7, enzymes producing lysophosphatidic acid and/or cyclic phosphatidic acid

GDE4 and GDE7 are membrane-bound enzymes that exhibit lysophospholipase D (lysoPLD) activities. We found that GDE7 produced not only lysophosphatidic acid (LPA) but also cyclic phosphatidic acid (cPA) from lysophospholipids by a transphosphatidylation reaction. In contrast, GDE4 produced only LPA. The analysis of substrate specificity showed that 1-alkyl-lysophosphospholipids were preferred substrates for both enzymes rather than 1-alkyl-lysophospholipids and 1-alkenyl-lysophospholipids. Among the various lysophospholipids with different polar head groups that were tested, lysophosphatidylglycerol and lysophosphatidylserine were preferred substrates for GDE4 and GDE7, respectively. The detailed analysis of the dependency of the enzyme activities of GDE4 and GDE7 on divalent cations suggested multiple divalent cations were bound in the active sites of both enzymes. Taken together, these results suggest the possibility that GDE7 functions as a cPA-producing enzyme in the body.

Haloarcula mannanilytica sp. nov., a galactomannan-degrading haloarchaeon isolated from commercial salt

A mannan-degrading halophilic archaeal strain, MD130-1^T, was isolated from a commercial salt sample. Cells were motile, rod-shaped, and stained Gram-negative. Colonies were pink pigmented. Strain MD130-1^T was able to grow at 1.5-4.6 M NaCl (optimum, 3.6 M) at pH 6.0-8.0 (optimum, pH 7.0) and at 25-50 °C (optimum, 40 °C). The DNA G+C content was 62.1 mol% (genome). The orthologous 16S rRNA gene sequence showed the highest similarity (99.4 %) to those of Haloarcula japonica JCM 7785^T and Haloarcula hispanica JCM 8911^T. The values of genome relatedness between strain MD130-1^T and Haloarcula species were 84.33-85.96 % in ANIb and 30.4-32.9 % using GGDC formula 2. The polar lipids of strain MD130-1^T were phosphatidylglycerol, phosphatidylglycerol phosphate methyl ester and triglycosyl diether-2. Based on the results of phenotypic and phylogenetic analyses, the strain represents a new species of the genus Haloarcula, for which the name Haloarcula mannanilytica sp. nov. is proposed. The type strain is MD130-1^T (=JCM 33835^T=KCTC 4287^T) isolated from commercial salt made in Ishikawa prefecture, Japan.

Eicosapentaenoic acid-containing polar lipids from seaweed Susabinori (Pyropia yezoensis) alleviate hepatic steatosis in obese db/db mice

Nonalcoholic fatty liver disease (NAFLD) is emerging as the most common liver disease in industrialized countries. Because hepatic steatosis is an early pathogenesis of NAFLD, the discovery of food components that could ameliorate hepatic steatosis is of interest. Susabinori (Pyropia yezoensis) is recognized as one of the most delicious edible brown algae, and we prepared lipid component of susabinori (SNL), which is rich in eicosapentaenoic acid (EPA)-containing polar lipids. In this study, we tested whether feeding SNL to db/db mice protects them from developing obesity-induced hepatic steatosis. After four weeks of feeding, hepatomegaly, hepatic steatosis, and hepatic injury were markedly alleviated in SNL-fed db/db mice. These effects were partly attributable to the suppression of activities and mRNA expressions of lipogenic enzymes and enhanced levels of adiponectin due to the SNL diet. Additionally, mRNA expression of monocyte chemoattractant protein-1, an inflammatory chemokine, was markedly suppressed, and the mRNA levels of PPARδ, the anti-inflammatory transcription factor, were strongly enhanced in the livers of db/db mice by the SNL diet. We speculate that the development and progression of obesity-induced hepatic steatosis was prevented by the suppression of chronic inflammation due to the combination of bioactivities of EPA, phospholipids, and glycolipids in the SNL diet.

A bidirectional crosstalk between glioblastoma and brain endothelial cells potentiates the angiogenic and proliferative signaling of sphingosine-1-phosphate in the glioblastoma microenvironment

Glioblastoma is one of the most malignant, angiogenic, and incurable tumors in humans. The aberrant communication between glioblastoma cells and tumor microenvironment represents one of the major factors regulating glioblastoma malignancy and angiogenic properties. Emerging evidence implicates sphingosine-1-phosphate signaling in the pathobiology of glioblastoma and angiogenesis, but its role in glioblastoma-endothelial crosstalk remains largely unknown. In this study, we sought to determine whether the crosstalk between glioblastoma cells and brain endothelial cells regulates sphingosine-1-phosphate signaling in the tumor microenvironment. Using human glioblastoma and brain endothelial cell lines, as well as primary brain endothelial cells derived from human glioblastoma, we report that glioblastoma-co-culture promotes the expression, activity, and plasma membrane enrichment of sphingosine kinase 2 in brain endothelial cells, leading to increased cellular level of sphingosine-1-phosphate, and significant potentiation of its secretion. In turn, extracellular sphingosine-1-phosphate stimulates glioblastoma cell proliferation, and brain endothelial cells migration and angiogenesis. We also show that, after co-culture, glioblastoma cells exhibit enhanced expression of S1P₁ and S1P₃, the sphingosine-1-phosphate receptors that are of paramount importance for cell growth and invasivity. Collectively, our results envision glioblastoma-endothelial crosstalk as a multi-compartmental strategy to enforce pro-tumoral sphingosine-1-phosphate signaling in the glioblastoma microenvironment.

de Rosales R. A bisphosphonate for 19F-magnetic resonance imaging

19F-magnetic resonance imaging (MRI) is a promising technique that may allow us to measure the concentration of exogenous fluorinated imaging probes quantitatively in vivo. Here, we describe the synthesis and characterisation of a novel geminal bisphosphonate (19F-BP) that contains chemically-equivalent fluorine atoms that show a single and narrow 19F resonance and a bisphosphonate group that may be used for labelling inorganic materials based in calcium phosphates and metal oxides. The potential of 19F-BP to provide contrast was analysed in vitro and in vivo using 19F-MRI. In vitro studies demonstrated the potential of 19F-BP as an MRI contrast agent in the millimolar concentration range with signal-to-noise ratios (SNR) comparable to previously reported fluorinated probes. The preliminary in vivo MRI study reported here allowed us to visualise the biodistribution of 19F-BP, showing uptake in the liver and in the bladder/urinary system areas. However, bone uptake was not observed. In addition, 19F-BP showed undesirable toxicity effects in mice that prevent further studies with this compound at the required concentrations for MRI contrast. This study highlights the importance of developing 19F MRI probes with the highest signal intensity achievable.

Branched phospholipids render lipid vesicles more susceptible to membrane-active peptides

Iso- and anteiso-branched lipids are abundant in the cytoplasmic membranes of bacteria. Their function is assumed to be similar to that of unsaturated lipids in other organisms - to maintain the membrane in a fluid state. However, the presence of terminally branched membrane lipids is likely to impact other membrane properties as well. For instance, lipid acyl chain structure has been shown to influence the activity of antimicrobial peptides. Moreover, the development of resistance to antimicrobial agents in Staphylococcus aureus is accompanied by a shift in the fatty acid composition toward a higher fraction of anteiso-branched lipids. Little is known about how branched lipids and the location of the branch point affect the activity of membrane-active peptides. We hypothesized that bilayers containing lipids with low phase transition temperatures would tend to exclude peptides and be less susceptible to peptide-induced perturbation than those made from higher temperature melting lipids. To test this hypothesis, we synthesized a series of asymmetric phospholipids that only differ in the type of fatty acid esterified at the sn-2 position of the lipid glycerol backbone. We tested the influence of acyl chain structure on peptide activity by measuring the kinetics of release from dye-encapsulated lipid vesicles made from these synthetic lipids. The results were compared to those obtained using vesicles made from S. aureus and Staphylococcus sciuri membrane lipid extracts. Anteiso-branched phospholipids, which melt at very low temperatures, produced lipid vesicles that were only slightly less susceptible to peptide-induced dye release than those made from the iso-branched isomer. However, liposomes made from bacterial phospholipid extracts were generally much more resistant to peptide-induced perturbation than those made from any of the synthetic lipids. The results suggest that the increase in the fraction of anteiso-branched fatty acids in antibiotic-resistant strains of S. aureus is unlikely to be the sole factor responsible for the observed increased antibiotic resistance. This article is part of a Special Issue entitled: Antimicrobial peptides edited by Karl Lohner and Kai Hilpert.

Lysylated phospholipids stabilize models of bacterial lipid bilayers and protect against antimicrobial peptides

Aminoacylated phosphatidylglycerols are common lipids in bacterial cytoplasmic membranes. Their presence in Staphylococcus aureus has been linked to increased resistance to a number of antibacterial agents, including antimicrobial peptides. Most commonly, the phosphatidylglycerol headgroup is esterified to lysine, which converts anionic phosphatidylglycerol into a cationic lipid with a considerably increased headgroup size. In the present work, we investigated the interactions of two well-studied antimicrobial peptides, cecropin A and mastoparan X, with lipid vesicles composed of 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) and 1-palmitoyl-2-oleoyl-phosphatidylglycerol (POPG), containing varying fractions of an aminoacylated phosphatidylethanolamine, a stable analog of the corresponding phosphatidylglycerol-derivative. To differentiate between the effects of headgroup size and charge on peptide-lipid interactions, we synthesized two different derivatives. In one, the headgroup was modified by the addition of lysine, and in the other, by glutamine. The modification by glutamine results in a phospholipid with a headgroup size comparable to that of the lysylated version. However, whereas lysyl-phosphatidylethanolamine (Lys-PE) is cationic, glutaminyl-phosphatidylethanolamine (Gln-PE) is zwitterionic. We found that binding of mastoparan X and cecropin A was not significantly altered if the content of aminoacylated phosphatidylethanolamines did not exceed 20mol.%, which is the concentration found in bacterial membranes. However, a lysyl-phosphatidylethanolamine content of 20mol% significantly inhibits dye release from lipid vesicles, to a degree that depends on the peptide. In the case of mastoparan X, dye release is essentially abolished at 20mol.% lysyl-phosphatidylethanolamine, whereas cecropin A is less sensitive to the presence of lysyl-phosphatidylethanolamine. These observations are understood through the complex interplay between peptide binding and membrane stabilization as a function of the aminoacylated lipid content. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.

Reduced glycerol incorporation into phospholipids contributes to impaired intra-erythrocytic growth of glycerol kinase knockout Plasmodium falciparum parasites

BACKGROUND

Malaria is a devastating disease and Plasmodium falciparum is the most lethal parasite infecting humans. Understanding the biology of this parasite is vital in identifying potential novel drug targets. During every 48-hour intra-erythrocytic asexual replication cycle, a single parasite can produce up to 32 progeny. This extensive proliferation implies that parasites require substantial amounts of lipid precursors for membrane biogenesis. Glycerol kinase is a highly conserved enzyme that functions at the interface of lipid synthesis and carbohydrate metabolism. P. falciparum glycerol kinase catalyzes the ATP-dependent phosphorylation of glycerol to glycerol-3-phosphate, a major phospholipid precursor.

METHODS

The P. falciparum glycerol kinase gene was disrupted using double crossover homologous DNA recombination to generate a knockout parasite line. Southern hybridization and mRNA analysis were used to verify gene disruption. Parasite growth rates were monitored by flow cytometry. Radiolabelling studies were used to assess incorporation of glycerol into parasite phospholipids.

RESULTS

Disruption of the P. falciparum glycerol kinase gene produced viable parasites, but their growth was significantly reduced to 56.5±1.8% when compared to wild type parasites. (14)C-glycerol incorporation into the major phospholipids of the parasite membrane, phosphatidylcholine and phosphatidylethanolamine, was 48.4±10.8% and 53.1±5.7% relative to an equivalent number of wild type parasites.

CONCLUSIONS

P. falciparum glycerol kinase is required for optimal intra-erythrocytic asexual parasite development. Exogenous glycerol may be used as an alternative carbon source for P. falciparum phospholipid biogenesis, despite the lack of glycerol kinase to generate glycerol-3-phosphate.

GENERAL SIGNIFICANCE

These studies provide new insight into glycerolipid metabolism in P. falciparum.

The importance of rhamnolipid-biosurfactant-induced changes in bacterial membrane lipids of Bacillus subtilis for the antimicrobial activity of thiosulfonates

The antimicrobial properties of methyl (MTS) and ethyl (ETS) esters of thiosulfonic acid alone and in combination with rhamnolipid-biosurfactant (RL) have been characterized for their ability to disrupt the normal physiological functions of living pathogens. Bactericidal and fungicidal activities of MTS and ETS and their combination with rhamnolipid were demonstrated on strains of Pseudomonas aeruginosa, Bacillus subtilis, Alcaligenes faecalis, and Rhizopus ngtricans. It was found that the combination of rhamnolipid and thiosulfonic esters has a synergistic effect leading to decreasing of bactericidal and fungicidal concentrations of MTS and ETS. More extensively was studied the effect of rhamnolipid on the lipid composition of B. subtilis bacterial membrane. To our knowledge, in this article is reported for the first time a remarkable increase of negatively charged phospholipid cardiolipin in the presence of rhamnolipid. The capacity of RL as a surface-active substance was confirmed by scanning electron microscopy (SEM). The occurrence of surface infolds and blebs on B. subtilis shown by SEM, was not accompanied by changes in membrane permeability tested by a live/dead viability staining for fluorescence microscopy. When RL was applied in combination with MTS, a dramatic permeability shift for propidium iodide was observed in vegetative cells.

TLR4 and NKT cell synergy in immunotherapy against visceral leishmaniasis

NKT cells play an important role in autoimmune diseases, tumor surveillance, and infectious diseases, providing in most cases protection against infection. NKT cells are reactive to CD1d presented glycolipid antigens. They can modulate immune responses by promoting the secretion of type 1, type 2, or immune regulatory cytokines. Pathogen-derived signals to dendritic cells mediated via Toll like Receptors (TLR) can be modulated by activated invariant Natural Killer T (iNKT) cells. The terminal β-(1–4)-galactose residues of glycans can modulate host responsiveness in a T helper type-1 direction via IFN-γ and TLRs. We have attempted to develop a defined immunotherapeutic, based on the cooperative action of a TLR ligand and iNKT cell using a mouse model of visceral leishmaniasis. We evaluated the anti-Leishmania immune responses and the protective efficacy of the β-(1–4)-galactose terminal NKT cell ligand glycosphingophospholipid (GSPL) antigen of L. donovani parasites. Our results suggest that TLR4 can function as an upstream sensor for GSPL and provoke intracellular inflammatory signaling necessary for parasite killing. Treatment with GSPL was able to induce a strong effective T cell response that contributed to effective control of acute parasite burden and led to undetectable parasite persistence in the infected animals. These studies for the first time demonstrate the interactions between a TLR ligand and iNKT cell activation in visceral leishmaniasis immunotherapeutic.

Kala azar (visceral leishmaniasis) is a deadly disease caused by the parasitic protozoa Leishmania donovani. In absence of a suitable vaccine, the incidence of leishmaniasis has increased. The World Health Organization observes that, if the disease is not treated, the fatality rate in developing countries can be as high as 100% within 2 years. Therapy of visceral leishmaniasis can be complicated by toxic side effects, drug resistance, and the need for prolonged treatment regimens. Therefore, improved therapy for leishmaniasis remains desirable. Immunotherapy to selectively induce type 1 immune responses considered essential for resistance to leishmaniasis has shown great promise. CD1d-binding glycolipids stimulate TCR signaling and activation of invariant natural killer T (iNKT) cells. Terminal β-(1–4)-galactose residues in glycoconjugates have been identified as the TLR ligand that induces IFN-γ via TLR signaling. We have used the β-(1–4)-galactose terminal glycosphingophospholipid (GSPL) antigen from L. donovani parasites to treat infected BALB/c mice. We report that immunotherapy with GSPL induced IFN-γ, a type 1 cytokine, through the cooperative action of TLR4 and NKT-cells that contributed to effective control of acute parasite burden in the infected animals.

Bacillus xiaoxiensis sp. nov., a slightly halophilic bacterium isolated from non-saline forest soil

A novel Gram-stain-positive, slightly halophilic, catalase-positive, oxidase-negative, endospore-forming, motile, facultatively anaerobic, rod-shaped bacterium, designated strain JSM 081004T, was isolated from non-saline forest soil in Xiaoxi National Natural Reserve, China. Growth occurred with 0.5–20 % (w/v) NaCl (optimum 2–4 %), at pH 6.0–10.5 (optimum pH 8.0) and at 5–40 °C (optimum 25–30 °C). meso-Diaminopimelic acid was present in the cell-wall peptidoglycan. The major cellular fatty acids were iso-C15 : 0 and anteiso-C15 : 0. Strain JSM 081004T contained MK-7 as the predominant respiratory quinone, and diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylglycerol as the major polar lipids. The genomic DNA G+C content of strain JSM 081004T was 40.1 mol%. Phylogenetic analysis based on 16S rRNA gene sequence comparisons revealed that strain JSM 081004T should be assigned to the genus Bacillus and was most closely related to the type strains of Bacillus lehensis (sequence similarity 97.8 %), Bacillus oshimensis (97.8 %) and Bacillus patagoniensis (97.3 %). Phylogenetic analysis, DNA–DNA relatedness values, phenotypic characteristics and chemotaxonomic data all support the proposal of strain JSM 081004T as a representative of a novel species of the genus Bacillus, for which the name Bacillus xiaoxiensis sp. nov. is proposed; the type strain is JSM 081004T ( = CCTCC AA 208057T  = DSM 21943T).

Lipid analysis by thin-layer chromatography--a review of the current state

High-performance thin-layer chromatography (HPTLC) is a widely used, fast and relatively inexpensive method of separating complex mixtures. It is particularly useful for smaller, apolar compounds and offers some advantages over HPLC. This review gives an overview about the special features as well as the problems that have to be considered upon the HPTLC analysis of lipids. The term "lipids" is used here in a broad sense and comprises fatty acids and their derivatives as well as substances related biosynthetically or functionally to these compounds. After a short introduction regarding the stationary phases and the methods how lipids can be visualized on an HPTLC plate, the individual lipid classes will be discussed and the most suitable solvent systems for their separation indicated. The focus will be on lipids that are most abundant in biological systems, i.e. cholesterol and its derivates, glycerides, sphingo- and glycolipids as well as phospholipids. Finally, a nowadays very important topic, the combination between HPTLC and mass spectrometric (MS) detection methods will be discussed. It will be shown that this is a very powerful method to investigate the identities of the HPTLC spots in more detail than by the use of common staining methods. Future aspects of HPTLC in the lipid field will be also discussed.

Leisingera nanhaiensis sp. nov., isolated from marine sediment

An aerobic, Gram-staining-negative, motile, rod-shaped bacterium, strain NH52FT, was isolated from a sandy sediment sample taken from the South China Sea. On M2 agar medium (a complex medium), colonies were beige in colour. The isolate showed highest 16S rRNA gene sequence similarities to members of the generaLeisingera(96.7 % similarity),Phaeobacter(95.4–96.0 %) andMarinovum(94.1 %). Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain NH52FTformed a distinct cluster withLeisingera methylohalidivoransMB2TandLeisingera aquimarinaLMG 24366T. Optimal growth was observed at pH 7.0-8.5 and 25 °C and the new isolate required the presence of 1–4 % (w/v) NaCl. The major fatty acids were C18 : 1ω7c, C16 : 02-OH, C10 : 03-OH, C12 : 03-OH, C16 : 0and 11-methyl C18 : 1ω7c. The DNA G+C content was 60.5 mol%. The phylogenetic and chemotaxonomic characteristics of strain NH52FTwere similar to those of the genusLeisingera. However, the differences in phenotypic properties and the 16S rRNA gene similarity values demonstrated that the new isolate differed from recognized species of the genusLeisingera. On the basis of phenotypic, chemotaxonomic and phylogenetic data, this organism should be classified as a representative of a novel species in the genusLeisingera, for which the nameLeisingera nanhaiensissp. nov. is proposed. The type strain is NH52FT(=LMG 24841T=CCTCC AB 208316T=MCCC 1A04178T).

The total synthesis of 2-O-arachidonoyl-1-O-stearoyl-sn-glycero-3-phosphocholine-1,3,1'-(13)C3 and -2,1'-(13)C2 by a novel chemoenzymatic method

2-O-Arachidonoyl-1-O-stearoyl-sn-glycero-3-phosphocholine was synthesized with carbon-13 enrichment of the three glycerol carbons and the carbonyl of the stearoyl group. Phospholipase A(2) was utilized to give optically pure lyso-PC, and only 3% acyl migration occurred during reacylation with arachidonic acid anhydride. This phospholipid is an important biosynthetic precursor of arachidonic acid metabolites as well as the endocannabinoid 2-arachidonoylglycerol (2-AG), and is now available for NMR studies.

Very-long-chain iso and anteiso branched fatty acids in N-acylphosphatidylethanolamines from a natural cyanobacterial mat of Calothrix sp

A combination of TLC, ESI-MS/MS and GC-MS was used to identify unusual molecular species of N-acylphosphatidylethanolamines containing very-long-chain anteiso branched fatty acids (VLCFAs) from Calothrix sp. collected in Antarctica and determine their component VLCFA up to 33-methyltetratriacontanoic acid as picolinyl ester derivatives using GC-MS.

Novel Long-circulating Liposomes Containing Peptide Library-lipid Conjugates: Synthesis andIn VivoBehavior

Rapid uptake of intravenously injected liposomes by the mononuclear phagocyte system has limited their use as drug delivery vehicles. Recently, various long-circulating liposomes have been prepared by incorporating glycolipids or other amphiphilic molecules into the lipid bilayer of conventional liposomes. The purpose of the present study was to design a new class of biodegradable membrane modifiers that would increase the half-life of liposomes in vivo. Using solid-phase peptide synthesis, synthesized were 30-residue random libraries consisting of a random sequence of glycine, beta-alanine and gamma-aminobutyric acid. The libraries were coupled to stearic acid (SA) or phosphatidylethanolamine (PE). The resulting amphiphilic conjugates were mixed with egg phosphatidylcholine (PC) and cholesterol (Chol) in a 6:47:47 ratio, and unilamellar liposomes were prepared. For comparison, plain PC/Chol (50:50) liposomes, as well as liposomes containing polyethylene glycol (PEG)-SA/PC/Chol (6:47:47) and PEG-PE/PC/Chol (6:47:47) were also prepared. Calcein was entrapped in the liposomes, which were given intravenously to rats at a dose of 9.2 mumol lipid/kg, and the amount of intact liposomes present in serum was followed with time. While the conventional liposomes had a short elimination half-life (28 min), the liposomes modified with library-PE had a much longer half-life (170 min), while library-SA provided no improvement of the liposome pharmacokinetics. PEG-PE greatly improved the half-life of the liposomes (400 min) while PEG-SA only provided a marginal improvement. All liposome preparations were cleared in a biphasic fashion. In conclusion, a novel biodegradable lipopeptide conjugate was designed that endows liposomes with a prolonged circulation time in vivo. The pharmacokinetic profile of these modified liposomes was drastically improved over that of conventional liposomes. Since the library is prepared by solid-phase synthesis, length and/or composition could easily be modified in order to modulate the clearance profile of the liposomes. Tailoring of the pharmacokinetic profile of the liposomes depending on their intended application may allow for a greater flexibility of use than PEG-PE.

Immuno stimulating glycophosphosphingolipid antigen from Leishmania donovani is recognized by visceral leishmaniasis patient sera

Surface antigens on Leishmania promastigotes and infected macrophages are obvious targets in immunoprophylaxis for leishmanial infection. The glycophosphosphingolipid (GSPL) antigen isolated from Leishmania donovani surface membrane was recognized by sera from patients with visceral leishmaniasis. GSPL was also expressed on the membrane of parasite-infected macrophages. The effect of GSPL on the production of reactive oxygen species (ROS) and reactive nitrogen intermediates (RNI) was studied using the macrophage cell line J774.1. In addition, induction of IFNgamma, IL4, IL10, IL12 secretion in presence of GSPL was investigated in PBMC from normal individuals. ROS and RNI in addition to IFNgamma and IL12 were induced by GSPL. Though there was a moderate induction of IL10, there was very little induction of the Th2 cytokine IL4. GSPL also induced blood cells to proliferate. The data suggests that this functionally important antigen of L. donovani may be used as a candidate vaccine.

Inactivation of Corynebacterium glutamicum NCgl0452 and the role of MgtA in the biosynthesis of a novel mannosylated glycolipid involved in lipomannan biosynthesis

Mycobacterium tuberculosis PimB has been demonstrated to catalyze the addition of a mannose residue from GDP-mannose to a monoacylated phosphatidyl-myo-inositol mannoside (Ac(1)PIM(1)) to generate Ac(1)PIM(2). Herein, we describe the disruption of its probable orthologue Cg-pimB and the chemical analysis of glycolipids and lipoglycans isolated from wild type Corynebacterium glutamicum and the C. glutamicum::pimB mutant. Following a careful analysis, two related glycolipids, Gl-A and Gl-X, were found in the parent strain, but Gl-X was absent from the mutant. The biosynthesis of Gl-X was restored in the mutant by complementation with either Cg-pimB or Mt-pimB. Subsequent chemical analyses established Gl-X as 1,2-di-O-C(16)/C(18:1)-(alpha-d-mannopyranosyl)-(1-->4)-(alpha-d-glucopyranosyluronic acid)-(1-->3)-glycerol (ManGlcAGroAc(2)) and Gl-A as the precursor, GlcAGroAc(2). In addition, C. glutamicum::pimB was still able to produce Ac(1)PIM(2), suggesting that Cg-PimB catalyzes the synthesis of ManGlcAGroAc(2) from GlcAGroAc(2). Isolation of lipoglycans from C. glutamicum led to the identification of two related lipoglycans. The larger lipoglycan possessed a lipoarabinomannan-like structure, whereas the smaller lipoglycan was similar to lipomannan (LM). The absence of ManGlcA-GroAc(2) in C. glutamicum::pimB led to a severe reduction in LM. These results suggested that ManGlcAGroAc(2) was further extended to an LM-like molecule. Complementation of C. glutamicum::pimB with Cg-pimB and Mt-pimB led to the restoration of LM biosynthesis. As a result, Cg-PimB, which we have assigned as MgtA, is now clearly defined as a GDP-mannose-dependent alpha-mannosyltransferase from our in vitro analyses and is involved in the biosynthesis of ManGlcAGroAc(2).

Cardiolipin induces premature senescence in normal human fibroblasts

Lipids seem to have various roles in cellular senescence. We found that cardiolipin very sensitively inhibits growth of normal human fibroblasts, whereas other phospholipids do not at 100 times higher concentrations. Growth arrested cells showed morphology similar to those of normally senesced cells and strongly induced senescence-associated beta-galactosidase. Senescence markers such as the p21(waf1/sdi-1), fibronectin, and collagenase-I genes were significantly upregulated by cardiolipin. In addition, caldiolipin significantly increased in normally senesced human fibroblasts leaving other phospholipids unaltered. These results suggest that accumulation of cardiolipin is one of the causes for replicative senescence.

SMP30 deficiency in mice causes an accumulation of neutral lipids and phospholipids in the liver and shortens the life span

Senescence marker protein-30 (SMP30) is an androgen-independent factor that decreases with aging. SMP30-deficient (SMP30Y/-) mice are viable and fertile but lower in body weight and shorter in life span than the wild-type. In the electron microscope, hepatocytes from SMP30Y/- but not the wild-type mice at 12 months of age clearly contained many lipid droplets, abnormally enlarged mitochondria with indistinct cristae, and enlarged lysosomes filled with electron-dense bodies. In liver specimens from SMP30Y/- mice, the marked number of lipid droplets visible around the central vein increased notably in size and amount as the animals aged. Biochemical analysis of neutral lipids, total hepatic triglyceride, and cholesterol from SMP30Y/- mice showed approximately 3.6- and 3.3-fold higher levels, respectively, than those from age-matched wild-type mice. Moreover, values for total hepatic phospholipids from SMP30Y/- mice were approximately 3.7-fold higher than those for their wild-type counterparts. By thin-layer chromatography analysis, phosphatidylethanolamine, cardiolipin, phosphatidylcholine, phosphatidylserine, and sphingomyelin accumulations were detected separately in lipid extracts from SMP30Y/- mouse livers and provided results that strongly indicate the profound effect of an SMP30 deficiency on the metabolism of these neutral lipids and phospholipids. Conceivably, this abnormality of lipid metabolism is sufficient to curtail the life span of SMP30-deficient mice.

Ether phospholipids and glycosylinositolphospholipids are not required for amastigote virulence or for inhibition of macrophage activation by Leishmania major

Ether phospholipids are major components of the membranes of humans and Leishmania. In protozoan parasites they occur separately or as part of the glycosylphosphatidylinositol (GPI) anchor of molecules implicated in virulence, such as lipophosphoglycan (LPG), smaller glycosylinositolphospholipids (GIPLs), and GPI-anchored proteins. We generated null mutants of the Leishmania major alkyldihydroxyacetonephosphate synthase (ADS), the first committed step of ether lipid synthesis. Enzymatic analysis and comprehensive mass spectrometric analysis showed that ads1- knock-outs lacked all ether phospholipids, including plasmalogens, LPG, and GIPLs. Leishmania ads1- thus represents the first ether lipid-synthesizing eukaryote for which a completely null mutant could be obtained. Remarkably ads1- grew well and maintained lipid rafts (detergent-resistant membranes). In virulence tests it closely resembled LPG-deficient L. major, including sensitivity to complement and an inability to survive the initial phase of macrophage infection. Likewise it retained the ability to inhibit host cell signaling and to form infectious amastigotes from the few parasites surviving the establishment defect. These findings counter current proposals that GIPLs are required for amastigote survival in the mammalian host or that parasite lyso-alkyl or alkylacyl-GPI anchors are solely responsible for inhibition of macrophage activation.

Utilization of liposomes in vesicular transport studies

Various coated vesicles are implicated in the intracellular transport between different compartments. In vitro reconstitution is a powerful experimental system to study molecular mechanisms involved in assembly of coat proteins from cytosol onto membranes as well as formation of coated vesicles. Liposomes have been recently utilized in the cell-free systems. In this review, we summarize studies on reconstitutions of coated vesicles or coated structures on liposomes. A novel method using dynamic light scattering (DLS) to quantify vesicle formation from liposomes also is described. Our recent study on the role of phospholipids in vesicle formation, where the DSL assay is used in combination with lipid analysis, also is introduced.

Phosphatidylinositol 4,5-bisphosphate stimulates vesicle formation from liposomes by brain cytosol

As a step toward the elucidation of mechanisms in vesicle budding, a cell-free assay that measures cytosol-induced vesicle generation from liposomes was established. This assay then was used to explore the role of phosphoinositides in vesicle formation. Liposomes incubated with brain cytosol in the presence of ATP and GTP massively generated small vesicles, as assessed both quantitatively and qualitatively by a dynamic light-scattering assay. Both ATP and GTP were required. Vesicle formation was inhibited greatly by the immunodepletion of dynamin 1 from the cytosol, indicating a major contribution of this GTPase in this reaction and suggesting that it mimics endocytic vesicle fission. Increasing the concentration of l-alpha-phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] but not of l-alpha-phosphatidylinositol 4-monophosphate or l-alpha-phosphatidylinositol in the lipid membranes enhanced vesicle formation. Lipid analysis revealed rapid degradation of PtdIns(4,5)P2 to l-alpha-phosphatidylinositol during the incubation with the reaction reaching a maximum within 5 sec, whereas vesicle formation proceeded with a longer time course. PtdIns(4,5)P2 degradation was independent of vesicle formation and occurred also in the presence of guanosine 5'-O-(thiotriphosphate), where few vesicle formations occurred. These results suggest that PtdIns(4,5)P2 plays a critical role in the early step of vesicle formation, possibly in the recruitment of coats and fission factors to membranes.

Synthesis of lipids on the micelle/water interface using inorganic phosphate and an alkene oxide

Liposomes can be considered as a model for a protocell in the context of the origin of life. These self-organising systems can self-reproduce under certain experimental conditions. Herein we demonstrate the ability of another lipid aggregate, micelles, to catalyse a reaction leading finally to the formation of new lipids. In contrast to other published work, where the lipids are products of a hydrolysis reaction, here the lipids are built up from simple precursors. In addition, we observe a transformation of micelles into liposomes.

N-acylated serinol is a novel ceramide mimic inducing apoptosis in neuroblastoma cells

A novel structural analog of ceramide was synthesized by N-acylation of serinol (2-amino-1,3-propanediol) and studied for its effects on glycolipid biosynthesis and cell differentiation of neuroblastoma cells. Incubation with N-palmitoylated serinol (C16-serinol) increased the concentration of endogenous ceramide by 50-80% and caused apoptosis in rapidly dividing low density cells but not in confluent cells. Cell death was not suppressed by simultaneous incubation with phorbol ester, known to antagonize ceramide-induced apoptosis by activation of protein kinase C (PKC). Purification of potential target proteins of C16-serinol was achieved by affinity chromatography of a protein preparation from rat brain on immobilized C16-serinol. A gel activity assay revealed that the eluate from C16-serinol-Sepharose contained three serine/threonine-specific protein kinases with molecular masses of 50, 70, and 95 kDa. The 70-kDa protein was immunostained on a Western blot using a PKCzeta-specific antibody. The purified PKCzeta could be activated directly by C16-serinol in an in vitro phosphorylation assay. Induction of apoptosis in neuroblastoma cells was suppressed by inhibition of PKCzeta with Gö 6983. Our overall results indicate that apoptosis in neuroblastoma cells induced by C16-serinol was at least partially mediated by activation of PKCzeta on condition of ongoing cell division. N-Acylated serinols may thus be useful for induction of apoptosis in mitotic cells and may be of therapeutic potential for treatment of cancer in the nervous system.

Existence of a bioactive lipid, cyclic phosphatidic acid, bound to human serum albumin

A novel bioactive lipid, cyclic phosphatidic acid (cPA), was identified in lipids bound to human serum albumin. A cPA fraction was extracted and purified from human serum albumin by use of a combination of preparative TLC and HPLC. Electrospray ionization mass spectrometry of the purified fraction showed molecular ions corresponding to cPA, which was composed of some different fatty acid species. The most abundant component was identified as palmitoyl-cPA by tandem mass spectrometry using collision-induced dissociation. These data have established that cPA is a naturally occurring lipid bound to human serum albumin.

Occurrence of an unusual phospholipid, phosphatidyl-L-threonine, in cultured hippocampal neurons. Exogenous L-serine is required for the synthesis of neuronal phosphatidyl-L-serine and sphingolipids

We have recently reported that L-serine released from astroglial cells supports the survival and neuritogenesis of hippocampal neurons under a serum- and glia-free culture condition (Mitoma, J., Furuya, S., and Hirabayashi, Y. (1998) Neurosci. Res. 30, 195-199). In this study, we show that exogenous L-serine is required for the synthesis of phosphatidyl-L-serine (PS) and sphingolipids in hippocampal neurons. When hippocampal neurons were maintained under an astroglial cell-free condition, the levels of sphingolipids and phosphatidyl-L-serine in the neurons were greatly reduced in the absence of external L-serine or glycine. Instead, a novel phospholipid appeared just ahead of PS on TLC. This novel lipid was determined to be phosphatidyl-L-threonine by TLC blotting/negative secondary ion mass spectrometry and amino acid analysis. Biochemical studies on rat brain microsomes have indicated that phosphatidyl-L-threonine is synthesized by the base exchange enzyme that is involved in PS synthesis with much lower affinity, that is, approximately (1)/(150) of L-serine. Addition of L-serine or glycine to the culture medium restored the synthesis of PS and sphingolipids in the neurons. These observations show that hippocampal neurons require exogenous L-serine for the synthesis of PS and sphingolipids in the absence of astroglial cells and suggested that astroglial cells contribute to neuronal lipid synthesis through the supply of L-serine.

Nanogram detection of phospholipids on thin-layer chromatograms

An extremely sensitive method for the quantitative determination of phospholipids on silica gel-precoated thin-layer chromatography plates is reported. The procedure is based on the successive application of two lipid spray reagents. Firstly, phospholipid chromatograms are sprayed with the lipophilic fluorochrome 1,6-diphenyl-1,3,5-hexatriene, followed by application of the phosphorus-specific molybdenum blue (Dittmer-Lester) reagent. Compared to the single use of the respective dyes, the consecutive utilization of both spray reagents resulted in an enormous enhancement in sensitivity of at least one order of magnitude. The procedure was proved with eight phospholipids of animal origin, and visual detection limits of down to 10 ng were achieved. The described technique provides a sensitive and specific means for the analysis of phospholipids on the nanogram scale by augmenting the molybdenum blue staining with the fluorochrome 1,6-diphenyl-1,3,5-hexatriene operating as an enhancer.

In vitro evaluation and characterization of newly designed alkylamidophospholipid analogues as anti-human immunodeficiency virus type 1 agents

Our laboratories first reported two novel classes of complex synthetic lipids, including alkylamidophosphocholines (PC lipid; CP-51) and alkylamidophosphate ester-linked lipid-AZT conjugates (lipid-AZT conjugates; CP-92), with selective and potent activity against human immunodeficiency virus type 1 (HIV-1). To extend these observations, we synthesized additional PC lipids and lipid-AZT conjugates (INK and INK-AZT conjugate) to evaluate their structure-activity relationships by testing for selectivity against infectious wild-type (wt) and drug-resistant HIV-1 replication, virus fusogenic activity and toxicity for mouse bone marrow cells. PC lipid compounds with medium chain lengths at positions 1 and 2 gave an improved selective index (SI). INK-3, with 12 and 8 carbons and INK-15, with 10 and 12 carbons were among the most selective when evaluated in CEM-SS cells. INK-14, a lipid-AZT conjugate where AZT replaced the choline in PC lipid INK-3, gave the highest SI of > 1250 against both infectious wt HIV-1 replication in CEM-SS cells and a clinical isolate in peripheral blood leukocytes. Notably, the PC lipid compounds INK-3 and INK-15, but not the lipid-AZT conjugate INK-14, were potent inhibitors of matched pairs of AZT-sensitive and AZT-resistant HIV-1 clinical isolates. INK-3 also inhibited replication of HIV-2 and TIBO-resistant HIV-1, and inhibited HIV-1-mediated fusogenic activity by 78, 41 and 9% in a dose-dependent manner. The TC50 for mouse bone marrow cells was > 100 micrograms/ml for INK-3 compared to 9.15-14.17 micrograms/ml for CP-51 and 0.142-0.259 microgram/ml for AZT. These data suggest that optimum PC lipid compounds are significantly less toxic than AZT and have high potential as novel therapeutic agents for AIDS.

Low density membranes are associated with RNA-binding proteins and thylakoids in the chloroplast of Chlamydomonas reinhardtii

Chloroplast subfractions were tested with a UV cross-linking assay for proteins that bind to the 5' untranslated region of the chloroplast psbC mRNA of the green alga Chlamydomonas reinhardtii. These analyses revealed that RNA-binding proteins of 30-32, 46, 47, 60, and 80 kD are associated with chloroplast membranes. The buoyant density and the acyl lipid composition of these membranes are compatible with their origin being the inner chloroplast envelope membrane. However, unlike previously characterized inner envelope membranes, these membranes are associated with thylakoids. One of the membrane-associated RNA-binding proteins appears to be RB47, which has been reported to be a specific activator of psbA mRNA translation. These results suggest that translation of chloroplast mRNAs encoding thylakoid proteins occurs at either a subfraction of the chloroplast inner envelope membrane or a previously uncharacterized intra-chloroplast compartment, which is physically associated with thylakoids.

Trapping of dextran-coated colloids in liposomes by transient binding to aminophospholipid: preparation of ferrosomes

A procedure is described that allows to increase the efficiency of the loading of liposomes with dextran-stabilized iron oxides (MION). The method produces a preparation of liposomes (REVs) with high iron oxide content as a result of transient binding of oxidized dextran with amino groups of aminophospholipids. Phosphatidylethanolamine (PE)-containing lipid mixtures (PC/DOPE/CH or SM/DOPE/CH, 9:2:9 molar ratio) in organic phase were combined with oxidized MION at pH 8. Liposomes then were obtained by reversed-phase evaporation. Liposomes, 263 +/- 89 nm in diameter, contained up to 11.8 mol Fe/mol phospholipid (encapsulation yield 49%). 10.2% of liposome-associated iron was dissociated from liposomes upon changing the pH to 4.5. When lipid compositions of extracts prepared from liposomes incubated at pH 4.5 and pH 8.0 were compared, an increase of relative PE-content in extracts of liposomes incubated at lowered pH was detected. This indicates a dissociation of imine bonds between aldehydes on the MION surface and PE. The accessibility of liposomal PE for acylation was demonstrated by modification with an activated ester of methoxy poly(ethylene glycol) succinate. Control liposomes, containing no aminophospholipid, or PE-containing liposomes obtained in the presence of non-oxidized MION, were 3.5-5-fold less effective for MION encapsulation and showed extensive aggregation.