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S J Turco

Publications and source records attributed to S J Turco.

At least 91 records · Page 5Linked to original sources
PubMed1990

The leishmanial lipophosphoglycan: a multifunctional molecule.

A striking characteristic of leishmanial parasites is their ability to avoid destruction in hostile environments throughout their life cycle. To survive, the parasites must have evolved specialized molecules. One such molecule that has received considerable attention is an unusual glycoconjugate called lipophosphoglycan. The macromolecule is the major cell surface glycoconjugate of all Leishmania promastigotes. This minireview summarizes current information on the structure and possible functions of this intriguing molecule.

Animals↗
PubMed1990

Characterization of Leishmania donovani variant clones using anti-lipophosphoglycan monoclonal antibodies.

Monoclonal antibodies directed against the lipophosphoglycan of Leishmania donovani were used to characterize two glycosylation variants of the parasite. One of the variants was found to be totally deficient in the synthesis and expression of lipophosphoglycan. The other variant synthesized lower levels (20%) of the glycoconjugate compared to wildtype cells and its lipophosphoglycan was smaller in size. The two lipophosphoglycan-deficient clones will be useful for elucidating the biosynthesis and function of the glycoconjugate.

Animals↗
PubMed1990

Expression of a repeating phosphorylated disaccharide lipophosphoglycan epitope on the surface of macrophages infected with Leishmania donovani.

Murine peritoneal macrophages were infected with living, virulent Leishmania donovani promastigotes. At intervals after infection, the macrophage surfaces were probed for the expression of lipophosphoglycan (LPG) epitopes by immunofluorescence with anti-LPG monoclonal antibodies. A repeating phosphorylated disaccharide epitope of LPG was detected as early as 5 to 10 min postinfection and was initially localized to the immediate area of internalization of the promastigote into the macrophage. The epitopes were evenly distributed over the entire macrophage surface by 25 min postinfection. Treatments which inhibited macrophage phagolysosomal degradation processes had no effect on epitope expression, whereas reagents that affected macrophage membrane flow and, thus, phagocytosis drastically reduced or abolished expression. Purified LPG or phosphoglycan, the delipidated form of the LPG molecule, was also shown to bind to a variety of different cell types in a temperature-independent manner. Since LPG has been implicated as having an immunoprotective role in leishmaniasis, these results suggest a further mechanism(s) by which Leishmania LPG might be involved in parasite pathogenicity and virulence.

Animals↗
PubMed1989

The immunochemical structure and surface arrangement of Leishmania donovani lipophosphoglycan determined using monoclonal antibodies.

Using intact Leishmania donovani promastigotes or purified L. donovani lipophosphoglycan (LPG) as immunogens, we have derived four LPG-specific monoclonal antibodies (MAbs). Two of these MAbs recognize an epitope consisting of the repeating phosphorylated galactose beta-1,4-mannose disaccharide portion of the molecule and cross-reacted with LPG from Leishmania major. These MAbs bound to the surface of living promastigotes of both species. The two other MAbs bound to the phosphosaccharide core structure of LPG and did not bind to the surface of living parasites, presumably due to masking of the core region. Experiments using all four MAbs with an LPG-deficient promastigote mutant indicated that both the repeat epitope and phosphosaccharide core were present in these cells, suggesting that incomplete assembly was responsible for the absence of intact LPG.

Animals↗
PubMed1989

Structure of the phosphosaccharide-inositol core of the Leishmania donovani lipophosphoglycan.

The phosphosaccharide-inositol core of the lipophosphoglycan of Leishmania donovani was generated by treatment of the glycoconjugate with mild acid and digestion with phosphatidylinositol-specific phospholipase C. The core was purified and examined by one- and two-dimensional 1H-1H NMR and by methylation analysis. From the results, the carbohydrate core was elucidated as a phosphosaccharide attached to the inositol residue of the lyso-alkylphosphatidylinositol anchor of lipophosphoglycan as follows: PO4----6GalP(alpha 1----6)GalP(alpha 1----3)Galf(alpha 1----3)ManP(alpha 1----3)ManP(alpha 1----4)GlcNP(alpha 1----6)myo-inositol. The presence of an internal galactofuranose residue is highly unusual and the ManP(alpha 1----4)GlcNP(alpha 1----6)myo-inositol sequence is homologous to the respective portion of the glycosylphosphatidylinositol anchors reported for both the Trypanosoma brucei variant surface glycoprotein and the rat brain Thy-1 glycoprotein.

Animals↗
PubMed1989

Inhibitory effects on protein kinase C activity by lipophosphoglycan fragments and glycosylphosphatidylinositol antigens of the protozoan parasite Leishmania.

Fragments of the lipophosphoglycan of Leishmania donovani were generated by phospholipase C digestion and mild acid hydrolysis. The fragments were purified and examined for inhibitory activity on protein kinase C isolated from rat brains. On a molar basis, the 1-O-alkylglycerol portion of LPG exhibited the most inhibitory activity, whereas the carbohydrate domain was not as effective. In addition, several glycolipid antigens from L. major, which contain short carbohydrate chains attached to phosphatidylinositol, were also efficient inhibitors of the enzyme. These results are consistent with the hypothesis that protein kinase C may be a key target for the parasites to overcome within host macrophages.

Animals↗
PubMed1989

Microbial glycolipids: possible virulence factors that scavenge oxygen radicals.

Two important pathogens of developing countries, Mycobacterium leprae, the etiologic agent of leprosy, and Leishmania donovani, the protozoal parasite that causes kalaazar, persist in the human host primarily in mononuclear phagocytes. The mechanisms by which they survive in these otherwise highly cytocidal cells are presently unknown. Since the best understood cytocidal mechanism of these cells is the oxygen-dependent system that provides lethal oxidants including the superoxide anion (O2-), hydrogen peroxide (H2O2), hydroxyl radical (OH), and singlet oxygen (1O2), we sought specific microbial products of these organisms that might enable them to elude oxidative cytocidal mechanisms. Phenolic glycolipid I of M. leprae and lipophosphoglycan of L. donovani are unique cell-wall-associated glycolipids produced in large amounts by the organisms. In this study, phenolic glycolipid I derivatives and lipophosphoglycan were examined for their ability to scavenge potentially cytocidal oxygen metabolites in vitro. Electron spin resonance and spin-trapping indicate that phenolic glycolipid I derivatives and lipophosphoglycan are highly effective in scavenging hydroxyl radicals and superoxide anions. The results suggest that complex glycolipids and carbohydrates of intracellular pathogens that can scavenge oxygen radicals may contribute to their pathogenicity and virulence.

Animals↗
PubMed1988

A ricin agglutinin-resistant clone of Leishmania donovani deficient in lipophosphoglycan.

A variant cell line of Leishmania donovani (named R2D2) has been selected for resistance to the cytotoxic lectin ricin agglutinin and shown to be defective in the synthesis of its major glycoconjugate lipophosphoglycan. Compared to the parental line, R2D2 cells showed a marked resistance to the toxic effects of ricin and an increased sensitivity toward concanavalin A. The synthesis of lipophosphoglycan by R2D2 cells was judged to be less than 1% relative to that of wildtype cells as determined by incorporation of radioactive mannose and galactose and by electrophoretic and chromatographic analyses. Although lacking lipophosphoglycan, R2D2 parasites were capable of infecting cultured U937 macrophages.

Animals↗
PubMed1988

The lipophosphoglycan of Leishmania.

The major cell surface glycoconjugate of leishmanial parasites is lipophosphoglycan (LPG). Its relative abundance, unique structure, and cellular location suggest one or more important roles in interactions between parasites and host cells. In this article, Sam Turco examines current information about this novel glycoconjugate and its significance.

Journal Article↗
PubMed1987

Inhibition of protein kinase C activity by the Leishmania donovani lipophosphoglycan.

Purified lipophosphoglycan from Leishmania donovani was found to inhibit the activity of protein kinase C isolated from rat brain. Protein kinase C inhibition by lipophosphoglycan was continuous for 30 minutes. The glycoconjugate was a competitive inhibitor with respect to diolein, a noncompetitive inhibitor with respect to phosphatidylserine, and had no significant effect on protein kinase M and protein kinase A. A possible physiological role of lipophosphoglycan as a negative effector of protein kinase C is suggested.

Animals↗
PubMed1987

Structure of the major carbohydrate fragment of the Leishmania donovani lipophosphoglycan.

The major carbohydrate fragment from the lipophosphoglycan of Leishmania donovani was generated by mild acid hydrolysis (0.02 N HCl, 5 min, 100 degrees C) and purified by chromatography on DE-52 cellulose and thin layer. By a combination of analyses including gas-liquid chromatography-mass spectrometry and 1H NMR, the structure of the fragment was elucidated as PO4----6Gal(beta 1----4)Man. Approximately 16 of these phosphorylated disaccharide units occur in the overall glycoconjugate structure. NMR analysis of an alkaline phosphatase treated phosphorylated tetrasaccharide generated from lipophosphoglycan showed that the phosphorylated disaccharide units are linked together via alpha-glycosidic linkages. Complete characterization of the phosphorylated disaccharide units of lipophosphoglycan provides the first example of a defined carbohydrate anchored in membranes by a derivative of phosphatidylinositol.

Animals↗
PubMed1987

Structure of the lipid moiety of the Leishmania donovani lipophosphoglycan.

The lipid moiety of the lipophosphoglycan of Leishmania donovani had been isolated and characterized as a novel lyso-alkylphosphatidylinositol. Treatment of lipophosphoglycan with either 10% NH4OH or a phosphatidylinositol-specific phospholipase C from Staphylococcus aureus liberated a monoalkylglycerol substituent. Structural characterization of the monoalkylglycerol by gas-liquid chromatography-mass spectrometry indicated the presence of two saturated, unbranched hydrocarbons: a C24 alkyl chain comprising 78% of the lipid with the remaining 22% as a C26 alkyl chain. Periodate sensitivity demonstrated that the alkyl side chain is linked to the C-1 position of the glycerol backbone. Treatment of lipophosphoglycan with nitrous acid released 1-O-alkylglycerophosphorylinositol due to an unacetylated glucosamine residue linked to the inositol of the lyso-alkylphosphatidylinositol. Quantitative analysis of the organic solvent-soluble product of nitrous acid deamination of lipophosphoglycan confirmed the expected ratio of inositol:phosphate:1-O-alkylglycerol as 1:1:1. These results suggest that L. donovani anchors its lipophosphoglycan with a unique lipid component.

Animals↗
PubMed1987

Cell surface lipophosphoglycan of Leishmania donovani.

Based on a galactose oxidase/NaB[3H]4 technique of radiolabeling macromolecules, the major glycoconjugate (lipophosphoglycan) of Leishmania donovani promastigotes was determined to be located on the cell surface. Incorporated radioactivity was analyzed by gel filtration on Sephadex G-100, chromatography on ricin agglutinin-coupled agarose, and lability to mild acid hydrolysis. Lipophosphoglycan was present throughout the various phases of growth of promastigotes, but was preferentially expressed during the latter part of logarithmic phase and in the stationary phase. In addition, metabolically labeled lipophosphoglycan was released into the culture medium. Expression of this unusual glycoconjugate on the cell surface of L. donovani suggests that it may play a major role in host cell-parasite interactions.

Animals↗
PubMed1985

Structure and assembly of the endoplasmic reticulum. Biosynthetic sorting of endoplasmic reticulum proteins.

We have studied the post-translational processing and the biosynthetic sorting of three protein components of murine endoplasmic reticulum (ER), ERp60, ERp72, and ERp99. In pulse-labeled MOPC-315 (where MOPC-315 represents mineral oil-induced plasmacytoma cells) plasmacytoma cells, no precursor forms of these proteins were detected and only ERp99 was sensitive to endoglycosidase H. The ERp99 oligosaccharide remained endoglycosidase H sensitive during a 3-h chase, and analysis by high performance liquid chromatography showed the predominant structure to be Man8GlcNAc2. We have used a sucrose gradient analysis of pulse-labeled MOPC-315 plasmacytoma cells in order to directly study the biosynthetic sorting of both glycosylated and nonglycosylated ERps and have found no strong evidence to suggest these proteins ever leave the endoplasmic reticulum. In spite of their common sorting pathway, these proteins differ in their membrane orientation. Both ERp60 and ERp72 are entirely protected by the endoplasmic reticulum membrane while ERp99 appears to have a large domain exposed on the cytoplasmic face of the endoplasmic reticulum.

Animals↗
PubMed1985

Separation of partially methylated mannitols by liquid chromatography.

To facilitate the methylation linkage analysis of complex carbohydrates containing radioactively labeled mannose residues, an HPLC micromethylation technique has been developed which effectively resolves all of the partially methylated mannitol standards prepared using an under-methylation protocol. The method was applied to the linkage analysis of the nine mannose residues of the dolichol-derived oligosaccharide Glc3Man9GlcNAc2 isolated from BHK-21 fibroblasts. This technique should prove widely applicable to the methylation linkage analysis of radiolabeled complex carbohydrates.

Animals↗