Isolation of ceramide-monomethylaminoethylphosphonate from the lipids of Tetrahymena pyriformis W

Genome analysis of sphingolipid metabolism-related genes in Tetrahymena thermophila and identification of a fatty acid 2-hydroxylase involved in the sexual stage of conjugation

Sphingolipids are bioactive lipids present in all eukaryotes. Tetrahymena thermophila is a ciliate that displays remarkable sphingolipid moieties, that is, the unusual phosphonate-linked headgroup ceramides, present in membranes. To date, no identification has been made in this organism of the functions or related genes implicated in sphingolipid metabolism. By gathering information from the T. thermophila genome database together with sphingolipid moieties and enzymatic activities reported in other Tetrahymena species, we were able to reconstruct the putative de novo sphingolipid metabolic pathway in T. thermophila. Orthologous genes of 11 enzymatic steps involved in the biosynthesis and degradation pathways were retrieved. No genes related to glycosphingolipid or phosphonosphingolipid headgroup transfer were found, suggesting that both conserved and innovative mechanisms are used in ciliate. The knockout of gene TTHERM_00463850 allowed to identify the gene encoding a putative fatty acid 2-hydroxylase, which is involved in the biosynthesis pathway. Knockout cells have shown several impairments in the sexual stage of conjugation since different mating types of knockout strains failed to form cell pairs and complete the conjugation process. This fatty acid 2-hydroxylase gene is the first gene of a sphingolipid metabolic pathway to be identified in ciliates and have a critical role in their sexual stage.

Phosphonate Biochemistry

Organophosphonic acids are unique as natural products in terms of stability and mimicry. The C-P bond that defines these compounds resists hydrolytic cleavage, while the phosphonyl group is a versatile mimic of transition-states, intermediates, and primary metabolites. This versatility may explain why a variety of organisms have extensively explored the use organophosphonic acids as bioactive secondary metabolites. Several of these compounds, such as fosfomycin and bialaphos, figure prominently in human health and agriculture. The enzyme reactions that create these molecules are an interesting mix of chemistry that has been adopted from primary metabolism as well as those with no chemical precedent. Additionally, the phosphonate moiety represents a source of inorganic phosphate to microorganisms that live in environments that lack this nutrient; thus, unusual enzyme reactions have also evolved to cleave the C-P bond. This review is a comprehensive summary of the occurrence and function of organophosphonic acids natural products along with the mechanisms of the enzymes that synthesize and catabolize these molecules.

New long chain bases in lipophosphonoglycan of Acanthamoeba castellanii

The polymer called lipophosphonoglycan (LPG) was isolated from Acanthamoeba castellanii membranes after exhaustive delipidation and butanol extraction. A novel extremely long phytosphingosine was revealed in glycoinositolphosphosphingolipid (GIPSL). All data obtained by gas-liquid chromatography coupled with MS analyses of products liberated during acid methanolysis and products of sodium metaperiodate and permanganate-periodate oxidations showed an unusual pattern of long chain bases (LCB) with branched bases (anteiso-C₂₄, anteiso-C₂₅, anteiso-C₂₆, iso-C₂₆, anteiso-C₂₇, and anteiso-C28) and normal ones (C₂₄, C₂₅, C₂₆, C₂₇). The phytosphingosines with hexa-, hepta-, and octacosanoic chains have not been detected in Acanthamoeba cells up to now. Also, the isomer configuration of long chain bases in LPG of A. castellanii was not defined in earlier reports. In the GC-MS chromatograms, the component forming a peak corresponding to anteiso-C₂₅ phytosphingosine was the most abundant and constituted more than 50 % of all LCB.

Detection and identification of Bacteriovorax stolpii UKi2 Sphingophosphonolipid molecular species

Bacteriovorax stolpii is a predator of larger gram-negative bacteria and lives as a parasite in the intraperiplasmic space of the host cell. This bacterium is unusual among prokaryotes in that sphingolipids comprise a large proportion of its lipids. We here report the presence of 18 molecular species of B. stolpii UKi2 sphingophosphonolipids (SPNLs). (31)P NMR spectroscopy and analysis of P(i) released by a differential hydrolysis protocol confirmed the phosphonyl nature of these lipids. The SPNLs were dominated by those with 1-hydroxy-2-aminoethane phosphonate (hydroxy-aminoethylphosphonate) polar head groups; aminoethylphosphonate was also detected in minor SPNL components. The long-chain bases (LCBs) were dominated by C(17) iso-branched phytosphingosine; C(17) iso-branched dihydrosphingosine was also present in some SPNLs. The N-linked fatty acids were predominantly iso-branched and most contained an alpha-hydroxy group (C(15) alpha-hydroxy fatty acid was the major fatty acid). Minor molecular species containing nonhydroxy fatty acids were also detected. The definitive iso-structures of the predominant fatty acids and LCBs present in the B. stolpii SPNLs were established using (13)C and (3)H nuclear magnetic resonance spectroscopy; less than 20% were unbranched. Detection and analyses of intact compounds by MS-MS were performed by a hybrid quadrupole time-of-flight (Q-TOF-II) MS equipped with an electrospray ionization source. Analyses of peracetylated derivatives verified the structural assignments of these lipids.

Sphingophosphonolipids, phospholipids, and fatty acids from Aegean jellyfish Aurelia aurita

The goal of this study is to elucidate and identify several sphingophosphonolipids from Aurelia aurita, an abundant but harmless Aegean jellyfish, in which they have not previously been described. Total lipids of A. aurita were 0.031-0.036% of fresh tissue, and the lipid phosphorus content was 1.3-1.7% of total lipids. Phosphonolipids were 21.7% of phospholipids and consisted of a major ceramide aminoethylphosphonate (CAEP-I; 18.3%), as well as three minor CAEP (II, III, IV) methyl analogs at 1.3, 1.1, and 1.0%, respectively. The remaining phospholipid composition was: phosphatidylcholine, 44.5%, including 36.2% glycerylethers; phosphatidylethanolamine, 18.6%, including 4.5% glycerylethers; cardiolipin, 5.6%; phosphatidylinositol, 2.6%; and lysophosphatidylcholine, 5.0%. In CAEP-I, saturated fatty acids of 14-18 carbon chain length were 70.8% and were combined with 57.3% dihydroxy bases and 23.4% trihydroxy bases. The suite of the three minor CAEP methyl analogs were of the same lipid class based on the head group, but they separated into three different components because of their polarity as follows: CAEP-II and CAEP-III differentiation from the major CAEP-I was mainly due to the increased fatty acid unsaturation and not to a different long-chain base, but the CAEP-IV differentiation from CAEP-I, apart from fatty acid unsaturation, was due to the increased content of hydroxyl groups originated from both hydroxy fatty acids and trihydroxy long-chain bases. Saturated fatty acids were predominant in total (76.7%), polar (83.0%), and neutral lipids (67.6%) of A. aurita. The major phospholipid components of A. aurita were comparable to those previously found in a related organism (Pelagia noctiluca), which can injure humans.

Phospholipid biosynthesis in protozoa

Because of the diverse nature of the organisms which are all classed as 'protozoa' (and because of the lack of detailed information on phospholipid metabolism about most of them), it will probably never be possible to generalize phospholipid metabolism to the degree that it has been possible to characterize a mammalian metabolism. Nonetheless, patterns have begun to emerge (i.e. the similarities among the ciliates Entodinium, Paramecium and Tetrahymena) and will not doubt be expanded upon in the future.

Isolation of goat spleen phosphonolipids by thin-layer chromatography: their identification and silicic acid column chromatographic separation

Goat spleen phosphonolipids were isolated by preparative thin-layer chromatography (TLC) using the solvent system methanol--water (2:1) and were identified by TLC, nitrogen--phosphorus determinations and IR spectroscopy. Silicic acid column chromatography of the isolated phosphonolipids confirmed the initial assignments.

Effect of modification of membrane phospholipid composition on the activity of phosphatidylethanolamine N-methyltransferase of Tetrahymena

The activity of phosphatidylethanolamine N-methyltransferase is less than 10% of control levels in microsomes prepared from the ciliate protozoan Tetrahymena thermophila whose phospholipid composition had been altered by being cultured on media containing phosphonic acids. The primary modification obtained is decreased levels of phosphatidylethanolamine (J.D. Smith and D.A. Giegel, Arch. Biochem. Biophys., 206, 420-423 (1981) and 213, 595-601 (1982)). The enzyme protein is present in these cells at normal levels since addition of the substrate phosphatidylethanolamine to the assay system restores enzyme activity of the lipid-modified microsomes to control levels, while the enzyme from control microsomes is not affected by added phosphatidylethanolamine. The microsomal enzyme is inhibited by the anionic phospholipids cardiolipin, phosphatidylglycerol, and phosphatidylinositol and by lysophosphatidylethanolamine while it is activated only by phosphatidylserine in addition to the substrates phosphatidylethanolamine and phosphatidyldimethylethanolamine. The added phosphatidylethanolamine acts directly as a substrate for the methyltransferase rather than acting by merely stimulating utilization of endogenous lipid since added phosphatidyl[14C]ethanolamine is directly converted to phosphatidylcholine. The results suggest that the technique of phosphonic acid-induced modification of lipid composition will be useful for the study of other membrane-bound enzymes.

Membranes of Tetrahymena. IV. Isolation and characterization of temperature-responsive smooth and rough microsomal subfractions

Temperature-responsive microsomes of the ciliate protozoan Tetrahymena have been originally fractionated by step centrifugation on two-layered, Mg2+-containing sucrose gradients. Three fractions have been obtained, which are termed smooth I, smooth II and rough according to the appearance of the membrane vesicles upon electron-microscopy. Smooth I, smooth II, and rough microsomes exhibit RNA/protein ratios of 0.09, 0.20, and 0.34; their phospholipid/protein ratios and their neutral lipid/phospholipid ratios were 0.52, 0.43 and 0.25, and 0.17, 0.18 and 0.13, respectively. All three fractions contain equivalent, low succinic dehydrogenase and 5'-nucleotidase activities. Glucose-6-phosphatase and acid phosphatase are more concentrated in smooth I membranes than in rough membranes. The reverse is true for ATPase. The smooth II membranes occupy an intermediate position except that their ATPase activity is the lowest of the three fractions. The specific activities of these enzymes of the three microsomal fractions are compared to those of homogenates of whole cells. Thin-layer chromatography reveals a very similar polar and nonpolar lipid pattern of the three microsomal fractions. The major phospholipid compounds are phosphatidlethanolamine, glycerideaminoethylphosphonate and phosphatidylcholine, while diglycerides, an unknown NL-compound, and triglycerides are the major apolar lipids. Gas liquid chromatography shows that the fatty acids are mainly even-numbered ranging between C12 and C18. The smooth I, smooth II and rough membranes contain 65.2, 69.3 and 72.7% unsaturated fatty acids in their polar lipids, whereas only 52.7, 49.7 and 48.3% unsaturated acids are found in their apolar lipids, respectively. The fatty acids are more unevenly distributed among the individual polar lipids than in the apolar ones.