Biosynthesis of bis(monoacylglyceryl)phosphate and acylphosphatidylglycerol in rat liver mitochondrial

Stereospecific synthesis of phosphatidylglycerol using a cyanoethyl phosphoramidite precursor

Phosphatidylglycerols (PG) are a family of naturally occurring phospholipids that are responsible for critical operations within cells. PG are characterized by an (R) configuration in the diacyl glycerol backbone and an (S) configuration in the phosphoglycerol head group. Herein, we report a synthetic route to provide control over the PG stereocenters as well as control of the acyl chain identity.

De novo biosynthesis of the late endosome lipid, bis(monoacylglycero)phosphate

Bis(monoacylglycero)phosphate (BMP) is a unique lipid enriched in the late endosomes participating in the trafficking of lipids and proteins through this organelle. The de novo biosynthesis of BMP has not been clearly demonstrated. We investigated whether phosphatidylglycerol (PG) and cardiolipin (CL) could serve as precursors of de novo BMP synthesis using two different cellular models: CHO cells deficient in phosphatidylglycerophosphate (PGP) synthase, the enzyme responsible for the first step of PG synthesis; and human lymphoblasts from patients with Barth syndrome (BTHS), characterized by mutations in tafazzin, an enzyme implicated in the deacylation-reacylation cycle of CL. The biosynthesis of both PG and BMP was reduced significantly in the PGP synthase-deficient CHO mutants. Furthermore, overexpression of PGP synthase in the deficient mutants induced an increase of BMP biosynthesis. In contrast to CHO mutants, BMP biosynthesis and its fatty acid composition were not altered in BTHS lymphoblasts. Our results thus suggest that in mammalian cells, PG, but not CL, is a precursor of the de novo biosynthesis of BMP. Despite the decrease of de novo synthesis, the cellular content of BMP remained unchanged in CHO mutants, suggesting that other pathway(s) than de novo biosynthesis are also used for BMP synthesis.

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

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

Characterization of N-acylphosphatidylethanolamine and acylphosphatidylglycerol in oats

Two polar lipid classes, both with three acyl groups, were isolated from an extract of oats and characterized by nuclear magnetic resonance spectroscopy, electrospray mass spectrometry (MS), and electron ionization MS (EIMS). Distortionless enhancement by polarization transfer (DEPT) and the two-dimensional correlation experiments 1H-detected heteronuclear multiple quantum coherence spectroscopy, heteronuclear multiple bond correlation spectroscopy, double quantum filtered correlation spectroscopy, and total correlation spectroscopy provided sufficient information for determination of the structure of the two lipid classes. The polar lipid classes were found to be N-acylphosphatidylethanolamine [1,2-diacyl-sn-glycero-3-phospho-(N-acyl)-1'-ethanolamine; N-acyl-PE] and acylphosphatidylglycerol [1,2-diacyl-sn-glycero-3-phospho-(3'-acyl)-1'-sn-glycerol]. High-performance liquid chromatography with electrospray ionization MS (HPLC-ESMS) and with electrospray ionization tandem MS (HPLC-MS/MS) were utilized for the separation and subsequent determination of molecular species. With HPLC-ESMS, ions of deprotonated molecules were obtained and with HPLC-MS/MS carboxylate ions (representing acyl groups) were obtained as well as other structurally significant ions. Fifty molecular species of N-acylphosphatidylethanolamine and 24 molecular species of acylphosphatidylglycerol were found, with a molecular mass range of 924-1032 Da and 959-1035 Da, respectively. Identification of the fatty acid isomers, as picolinyl ester derivatives, was done with gas chromatography with EIMS. Three isomers of 16:1 fatty acids were found in N-acyl-PE, and their double bond positions were determined to 6, 9, and 11 with a relative abundance of 4:10:1.

Cardiolipin is synthesized from exogenous phosphatidylglycerol in rat heart

De novo biosynthesis of phosphatidylglycerol and cardiolipin in the isolated intact rat heart was shown to occur from newly synthesized phosphatidic acid via the formation of cytidine-5'-diphosphate-1,2-diacylglycerol (Hatch, G.M. (1994) Biochem. J. 297, 201-208). The biosynthesis of new cardiolipin was investigated in isolated rat hearts perfused with exogenous phosphatidylglycerol. Phosphatidylglycerol was rapidly (within 5 min) incorporated into the heart when hearts were perfused with either phosphatidyl-[14C]glycerol or NBD-phosphatidylglycerol. In hearts perfused with phosphatidyl-[14C]glycerol for up to 30 min the amount of radioactivity observed in phosphatidylglycerol was maximum by 5 min of perfusion and remained constant throughout the perfusion period. In the presence of 1-50 microM phosphatidylglycerol, the amount of radioactive phosphatidylglycerol incorporated into the heart was not affected. There was a time-dependent accumulation of radioactivity incorporated into cardiolipin. In addition, radioactivity was incorporated with time into lysophosphatidylglycerol. No significant amount of radioactivity was associated with other phospholipids involved in the biosynthesis of cardiolipin, including phosphatidic acid and cytidine-5'-diphosphate-1,2-diacylglycerol, precursors of cardiolipin biosynthesis via the CDP-DG pathway. We postulate that cardiac cardiolipin may be synthesized from exogenous phosphatidylglycerol independent of phosphatidylglycerol synthesized within the heart.

Lysosomal phosphatidylcholine: bis(monoacylglycero)phosphate acyltransferase: specificity for the sn-1 fatty acid of the donor and co-purification with phospholipase A1

Positional specificities in donor and acceptor phospholipids of the lysosomal phosphatidylcholine: bis(monoacylglycero)phosphate acyltransferase have been determined. Comparison of the transfer of labelled fatty acid from sn-1 [14C]acyl and sn-2 [14C]acylphosphatidylcholines by extracts of rat liver lysosomes revealed that fatty acids in the sn-1 position were exclusively transferred. Degradation of the acylphosphatidylglycerol product by Rhizopus arrhizus lipase, highly specific for fatty acids esterified to sn-1 or sn-3 positions, indicated that sn-1 or sn-3 rather than sn-2 positions had been acylated. Assays of phospholipase A1, phosphatidylcholine: bis(monoacylglycero)phosphate acyltransferase, the conversion of lysophosphatidylglycerol to bis(monoacylglycero)phosphate and phospholipase A2 were performed at various steps in the purification of lysosomal phospholipase A1. After the penultimate step of chromatofocusing, there was a 1086-fold increase of phospholipase A1 specific activity over the homogenate and this was accompanied by a 11 998-fold increase of phosphatidylcholine: bis(monoacylglycero)phosphate acyltransferase specific activity. A second preparation carried through to the final step of gel-filtration retained a similar ratio of acyltransferase activity. On the other hand, specific activities of phospholipase A2 and of the conversion of lysophosphatidylglycerol to bis(monoacylglycero)phosphate increased to the step where enzyme was solubilized from lysosomes, but were lost from later steps. These findings suggest that phosphatidylcholine: bis(monoacylglycero)phosphate acyltransferase is catalyzed by lysosomal phospholipase A1. The site of acylation in the bis(monoacylglycero)phosphate acceptor appears to be either sn-1 or sn-3. Since the lysosomal extracts did not catalyze the transacylation of phosphatidylglycerol, we conclude that the formation of acylphosphatidylglycerol in lysosomes requires the sequential acylation of lysophosphatidylglycerol to form bis(monoacylglycero)phosphate by an unidentified enzymatic mechanism followed by a transacylation of bis(monoacylglycero)phosphate in either sn-1 or sn-3 position to form acylphosphatidylglycerol which is catalyzed by phospholipase A1.

Formation of bis(monoacylglycero)phosphate by a macrophage transacylase

Formation of bis(monoacylglycero)phosphate (BMP) from lysophosphatidyl[U-14C]glycerol was studied in rabbit pulmonary alveolar macrophages. The majority of the activity was found in the particulate fraction (lysosome-enriched) sedimenting between 2000 and 12,000 rpm and it was maximal at pH 4.5. The activity in this fraction was stimulated by 2-mercaptoethanol and additional lipids from the fraction and inhibited by 5 mM CaCl2, 0.5 mM acyl-CoA, 1.0 mM chlorpromazine and by detergents, whereas chloroquine, cholesterol and butanol had no effect. The activity was retained by the particles after repeated freezing and thawing. After treatment with n-butanol, most of the activity was lost, but 84% could be recovered in the aqueous phase if the butanol-extracted lipids were added back giving an activity of 266 nmol/h per mg of protein. Lipids most effective in restoring activity were the total lipids extracted by butanol from the particulate fraction, fractions of the total lipids containing phospholipids and phosphatidylcholine from both native and commercial sources, with native BMP and commercial phosphatidylglycerol and sphingomyelin having a much smaller effect. The complexity of the lipid requirements was further indicated by the finding that addition of pure lipids to the total lipid extract reduced the efficacy of the latter. A direct transfer of [14C]oleic acid to BMP from labelled macrophage microsomal lipids was catalyzed by the soluble enzymes as was transfer from dioleoylphosphatidylcholine in the presence of lysophosphatidylglycerol. The particulate enzyme also catalyzed the transfer of [14C]oleic acid from 2-oleoylphosphatidylcholine to BMP in the presence of lysophosphatidylglycerol. These findings indicate that the transacylase involved in conversion of lysophosphatidylglycerol to BMP utilizes complex lipids other than phosphatidylinositol as acyl donors and has complex requirements for lipids as physicochemical activators. They further suggest that the transacylation might be catalyzed by lysosomal phospholipase A2.

A new synthesis of bis(diacylglycero)phosphate

The chemical synthesis of bis(diacylglycero) phosphate previously named bisphosphatidic acid, starting with a diacylglycerol and phosphatidic acid, is described. The phosphodiester bond formation is catalyzed by triisopropylbenzenesulfonylchloride. This simple approach allows the preparation of saturated as well as unsaturated bis(diacylglycero)phosphate species in one step without the use of any protecting group. The methods used until now yield only mono-acid species, or mixed-acid unsaturated species after many steps involving the introduction and the removal of protecting groups. The synthetic products have been characterized by component analysis and NMR-techniques.

The stereoconfiguration of newly formed molecules of bis(monoacylglycero)phosphate in BHK cells

Newly formed molecules of bis(monoacylglycero)phosphate (known also as lysobisphosphatidic acid), which were labeled with 32Pi in cultured BHK cells during relatively short pulses, were subjected to stereoanalysis. In contrast to the high proportion of sn-1-glycerophosphate residues in the bulk of the bis(monoacylglycero)phosphate molecules, the newly formed molecules were rich in sn-3-glycerophosphate residues.

The mechanism of modification by propranolol of the metabolism of phosphatidyl-CMP (CDP-diacylglycerol) and other lipids in the rat pineal gland

The mechanism underlying the alteration of phospholipid metabolism in rat pineal gland in vitro produced by propranolol and tertiary amine local anesthetics was investigated. 0.1 mM propranolol did not affect either the levels or specific activity of [32P]ATP in glands. In the presence of the drug, the incorporation of cytidine, but not of inorganic phosphate, into phosphatidyl-CMP (CDP-diacylglycerol) was dependent on the cytidine concentration. The incorporation of glycerol into phosphatidyl-CMP, phosphatidylinositol and phosphatidylglycerol was enhanced by propranolol, whereas labeling of phosphatidylcholine was decreased. When both 1 mM propranolol and 1 mM inositol were present, labeling of phosphatidylinositol was further increased, stimulation of phosphatidyl-CMP and phosphatidylglycerol labeling was reduced and incorporation into phosphatidylcholine and triacylglycerol was depressed. The incorporation of [3H]inositol into pineal lipids was also enhanced by propranolol. 10 microM propranolol inhibited rat liver phosphatidic acid phosphohydrolase by 50%, while local anesthetics were less potent in the decreasing order: dibucaine greater than tetracaine greater than lidocaine greater than procaine. The propranolol-induced accumulation of phosphatidyl-CMP was prevented by supplying adequate freely diffusible inositol in the medium. The phosphatidyl-CMP which accumulated was not utilized for the enhanced formation of phosphatidylinositol brought about by norepinephrine. The results indicate that propranolol and local anesthetics redirect pineal phospholipid metabolism in part by inhibition of phosphatidic acid phosphohydrolase.

Identification and synthesis of acyl-phosphatidylglycerol in Acinetobacter sp. HO1-N

A minor phospholipid from Acinetobacter sp. HO1-N was identified as acyl-phosphatidylglycerol. Acyl-phosphatidylglycerol synthesis by outer-membrane preparations appeared to be a result of phospholipase A activity.

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

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

The stereochemical configuration of lysobisphosphatidic acid from rat liver, rabbit lung and pig lung

Lysobisphosphatidic acid known also as bis(monoacyl-glycerol)phosphate, was isolated from liver of rats treated with Triton WR1339, and from rabbit and pig lung. Alkaline hydrolysates of all these samples of lysobisphosphatidic acid were essentially similar and contained phosphorus, total glycerol, free glycerol, total glycerophosphates, beta-glycerophosphate, total alpha-glycerophosphates, sn-glycero-1-phosphate and sn-glycero-3-phosphate in a molar ratio of 1.0 : 2.0 : 1.0 : 1.0 :0.6 : 0.4 : 0.38 : 0.04. This proves that the backbone of the principal lysobisphosphatidic acid from all three sources has the structure of 1-sn-glycerophospho-1-sn-glycerol.

Studies on nucleotide diphosphate diacylglycerol specificity of acidic phospholipid biosynthesis in rat liver subcellular fractions

(1)Cytidine diphosphate diacylglycerol, uridine diphosphate diacylglycerol, adenosine diphosphate diacylglycerol and guanosine diphosphate diacylglycerol were synthesized chemically and their purity assessed. The acticity of these compounds in acidic phospholipid synthesis was examined in rat liver mitochondria and microsomes. (2) Phosphatidylglycerol synthesis in rat liver mitochondria exhibited considerable activity with CDP diacylglycerol (v 7.0 nmol mg-1 h-1). UDPdiacylglycerol (v 5.4) and ADP diacylglyc erol (v 4.2). GDP diacylglycerol activity was detectable but very low. (3) Diphophatidylglycerol formation in mitochondria and phosphatidylinositolsythesis in microsomes exhibited considerable more specificity for CDP diacylglycerol. However, at high concentrations, measurable diphosphaticylglycerol and phophatidylinositol synthesis was observed with the other liponucleotides. (4) Although considerable phosphatidylglycerol formation was observed with UDPdiacaylglycerol and ADP diacylglycerol, it is unlikelky that these compounds are of physiologic importance, at least in rat liver, since CTP:phophatidic acid cytidyltransferase in microsomes and mitochondria was shown to be specific for cytidine triphosphate. The lack of specificity of phosphatiidylglycerol synthesis for CDP diacylglycerol is currently unexplained but may be of some importance in other tissues or in other organisms.