Synthesis of fluorescent lactosylceramide stereoisomers

The intracellular distribution of synthetic glycosphingolipids (GSLs) bearing a fluorophore can be monitored in living cells by fluorescence microscopy. We reported previously that variation in the length of the long-chain base and in the structure of the carbohydrate-containing polar head group of (2S,3R) (or D-erythro-)-beta-lactosylceramide (LacCer) did not alter the mechanism of endocytic uptake from the plasma membrane of various mammalian cell types [Singh, R.D., Puri, V., Valiyaveettil, J.T., Marks, D.L., Bittman, R., Pagano, R.E., 2003. Selective caveolin-1-dependent endocytosis of glycosphingolipids. Mol. Biol. Cell 14, 3254-3265]. To extend our examination of the molecular features in LacCer that are responsible for its uptake by the caveolar-requiring endocytic pathway, we have synthesized the three unnatural stereoisomers [(2R,3R)-, (2S,3S)-, and (2R,3S)] of dipyrromethene difluoride (BODIPY)-LacCer. These analogues will be used to probe the role of stereochemistry in the long-chain base of LacCer in the mechanism of endocytic uptake.     

Developmental expression of the type I diabetes related antigen sulfatide and sulfated lactosylceramide in mammalian pancreas

Previous studies have shown that sulfatide is present and functionally involved in beta cells, and that anti-sulfatide antibodies (ASA) exist during development of type I diabetes mellitus. To further explore the possible role of sulfatide in type I diabetes, developmental expression was examined in human pancreas and in pancreas of the type I diabetes models BB rat and NOD mouse compared to Lewis rat and BALB/c mouse, respectively. Sulfatide was not only expressed in adult pancreas, but also in human fetal and rodent neonatal pancreas, i.e., during the growing period of the immunological self. Sulfatide had a different expression pattern in human beings and rodents, concerning both the amounts of sulfatide and expression during development. There was no change in the sulfatide fatty acid isoform expression during development. The pancreatic expression of another sulfated glycosphingolipid, sulfated lactosylceramide, indicated that this molecule is a potential fetal/neonatal marker, which was further expressed in the type I diabetic models. In conclusion, these findings give further support to the possibility that sulfatide is a relevant autoantigen in type I diabetes and that sulfated lactosylceramide might function as a potential risk factor for disease development, at least in the animal models.     

Studies of the action of ceramide-like substances (d- andl-PDMP) on sphingolipid glycosyltransferases and purified lactosylceramide synthase

We have studied the effects ofD-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP) and itsL-enantiomer on glycosphingolipids in cultured normal human kidney proximal tubular cells. We found thatD-PDMP exerted a concentration-dependent reduction in the metabolic labelling and cellular levels of glucosylceramide (GlcCer), lactosylceramide (LacCer), and the globo-series glycosphingolipids, GbOse₃Cer and GbOse₄Cer. It also directly inhibited the activity of UDP-glucose:ceramide 1 4-glucosyltransferase (GlcT-1) and UDP-galactose: GlcCer 1 4 galactosyltransferase (GalT-2). In contrast,L-PDMP had opposite effects on the metabolic labelling of GlcCer, LacCer, and GbOse₃Cer. The levels of GlcCer and LacCer were increased, while the labelling and level of GbOse₄Cer were strongly reduced. Purified GalT-2 from human kidney was inhibited byD-PDMP and stimulated byL-PDMP. It appears likely that the different glycosphingolipid glycosyltransferases possess similar binding sites for the ceramide moiety, which are blocked by binding toD-PDMP and, in the case of GbOse₄Cer synthase, byL-PDMP as well. The stimulatory effects ofL-PDMP on GlcCer and LacCer synthases may be the result of binding to a modulatory site on the glycosyltransferases; in intact cells, the enzyme-analog complex may afford protection against the normal catabolic inactivation of the enzymes.Abbreviations GalT-2 UDP-galactose:GlcCer -galactosyltransferase - GbOse₃Cer Gal1 4Gal1 GlcCer - GbOse₄Cer GalNAc1 3Gal1 4Gal1 GlcCer - GlcCer glucosylceramide - GlcT-1 UDP-glucose:ceramide -glucosyltransferase - GSLs glycosphingolipids - LacCer lactosylceramide - PDMP threo-1-phenyl-2-decanolyamino-3-morpholino-1-propanol     

Synthesis of the 15N-Gln11 labeled peptaibol antibiotic zervamicin-IIB

Summary Synthesis of zervamicin IIB, specifically labeled at the α-position of glutamine-11 with¹⁵N, was achieved by the Fmoc/tert.-butyl strategy in solution using a fragment condensation approach. Three fragments of zervamicin IIB were obtained by stepwise elongation with Fmoc amino acids using BOP as a coupling reagent. For the introduction of the highly sterically hindered α-aminoisobutyric acid residues, BOP/DMAP activation was applied. Peptide fragments were coupled by means of the coupling reagent, CF₃-PyBOP. Using the strategy developed, zervamicin IIB specifically¹⁵N labeled has been synthesized in 30% overall yield based on the isotopically labeled amino acid. From 600 MHz NMR spectroscopy the position of the¹⁵N-label was clearly detected. The isotope enrichment (98 ±2%) was determined by FAB-mass spectrometry.     

Organometallic Intermediates in the Synthesis of Nucleoside Analogs

Abstract

The common nucleosides, modified or derivatized in some way at the heterocyclic ring carbons, include examples of structures which a r e useful as biological probes and chemotherapeutic agents. Like previous authors, we will use the term “nucleoside analog” for structures related to one of the common naturally occurring nucleosides. Nucleosicle analogs can be derivatives which differ by such minor modification as replacement of hydrogen by a single atom or derivatives which are grossly modified at both the carbohydrate and the base. Examples of the former include 5-fluoro-2′-deoxyuridine, an inhibitor of thymidylate synthetase as its 5′-phosphate, and 5′-iodo-2′-deoxyuridine, a clinically useful antiviral agent. Larger groups have frequently been linked to nucleoside as probes for enzymatic processes. Side chains in “nonrestricted positions” may be used to carry spectroscopic or chemically reactive probes, or provide the means to attach a molecule to an affinity column. Ultimately with positions of bulk tolerance defined, it may be possible to design “active site directed irreversible enzyme inhibitors” as defined by B.R. Baker. Nucleoside structures in which a side chain is attached at a pyrimidine or purine carbon will undoubtedly, in some instances be the most appropriate structure. Yet, these have typically been more difficult to synthesize than analogs with side chains attached to heteroatoms.     

Phosphorylation of human interleukin-2 (IL-2)

Human interleukin-2 (IL-2) is a lymphokine which is capable of activating lymphocytes and supporting the long-term in vitro growth of activated T cell clones. Recombinant human IL-2, expressed in either E. coli or cos cells, was shown to be phosphorylated by protein kinase C. Phosphorylated IL-2 synthesized in E. coli was analyzed by SDS-PAGE, reverse phase HPLC, and tryptic peptide mapping. The phosphorylated tryptic peptide was identified as the N-terminal fragment containing a single phosphorylation site at the serine residue at position 7. There was no difference in biological activity between non-phosphorylated and phosphorylated IL-2, as determined by a T cell growth assay. Although the physiological role of phosphorylation of IL-2 is unclear, IL-2 can be labeled with [-^32p] ATP and protein kinase C to a high specific radioactivity, and the synthesis of biologically active ^32p-labeled IL-2 may be useful for receptor-binding studies of the cells containing low level of phosphoprotein phosphotases.Abbreviations IL-2 Interleukin-2 - rIL-2 recombinant IL-2 - SDS-PAGE Sodium Dodecylsulfate Polyacrylamide Gel Electrophoresis, Tris tris (hydroxymethyl)-amino methane - RP-HPLC Reverse Phase High Pressure Liquid Chromatography - PTH Phenylthiohydantoin - IFN- Leukocyte Interferon - IFN- Fibroblast Interferon - IFN- Immune Interferon By acceptance of this article, the publisher or recipient acknowledges the right of the U.S. Government to retain a nonexclusive, royalty-free license in and to any copyright covering the articleResearch being carried out at the Frederick Cancer Research Facility, Frederick, Maryland     

The Southern blot

This article is devoted to the recent advances made in the Southern blotting technique, which is used for the detection of gel-fractionated DNA molecules following transfer to a membrane. The latest practical improvements made to the techniques of Southern blotting, probe labeling, and hybridization are discussed. Among the most significant advances are: new membranes, transfer methods, probe labeling, and rapid hybridization. Detailed protocols show the application of these improvements in this widely used technique.     

Computer analysis of double-labeled two-dimensional electrophoresis gels

A computerized process for the automatic analysis of double-label autoradiography after two-dimensional polyacrylamide gel electrophoresis has been developed. Matching fluorographs and autoradiographs produced from gels containing 3H- and 14C-labeled proteins are digitized by a rotating drum densitometer and analyzed by the Man-computer Interactive Data Analysis System III. This system locates corresponding protein spots in the films with edge-detection algorithms, converts spot density readings to isotopic disintegrations by reference to standard curves, and computes a 3H:14C ratio for each spot in the gels. On the average, calculated ratios are accurate to approximately 9% for test strips of polyacrylamide gel containing uniform mixtures of 3H and 14C. Values obtained for two-dimensional gels containing n protein spots with a known 3H:14C ratio of 8.6 +/- 0.1 are as follows: 8.1 +/- 1.4 (n = 268), 8.8 +/- 2.1 (n = 278), 9.1 +/- 1.7 (n = 245), and 8.8 +/- 2.2 (n = 223). The computer process greatly reduces the time required to precisely compare two complex protein mixtures and has sufficient precision to detect a doubling in the biosynthesis of any individual protein.     

Synthesis of an Agonistic,Difluoro-Azido Photolabel of Angiotensin II and Labeling of the AT1 Receptor: Transmembrane Domains 3, 6, and 7 Form the Ligand-Binding Pocket

p-Azido-phenylalanine has been frequently used for photoaffinity labeling of target proteins such as the angiotensin receptors. However, chemical studies showed that simple aryl nitrenes first react intramolecularly, forming a semistable cyclic keteneimine and then reacting with nucleophile residues in the target structure like those of lysine and arginine. We synthesized 3,5-difluoro-4-azidophenylalanine where the formation of the keteneimine is prevented and where photoincorporation should be due to nonselective nitrene insertion only. This new amino acid was introduced in position 8 of angiotensin II and compared with the corresponding azidophenylalanine peptide using human AT₁ receptor as target. The new photolabel maintained full agonist activity and a similar yield of photolabeling but without the previously observed gradual hydrolysis. Several selective proteolyses of the labeled receptor indicate that the new photolabel forms three simultaneous contact regions on the hAT₁ receptor, suggestive of a nonselective behavior of the photolabel. A major contact was established in the sixth transmembrane domain but also in the third and seventh domain. Our results are in excellent agreement with those recently obtained from methionine proximity assay studies.     

Synthesis and site-directed fluorescence labeling of azido proteins using eukaryotic cell-free orthogonal translation systems

Eukaryotic cell-free systems based on wheat germ and Spodoptera frugiperda insect cells were equipped with an orthogonal amber suppressor tRNA–synthetase pair to synthesize proteins with a site-specifically incorporated p-azido-l-phenylalanine residue in order to provide their chemoselective fluorescence labeling with azide-reactive dyes by Staudinger ligation. The specificity of incorporation and bioorthogonality of labeling within complex reaction mixtures was shown by means of translation and fluorescence detection of two model proteins: β-glucuronidase and erythropoietin. The latter contained the azido amino acid in proximity to a signal peptide for membrane translocation into endogenous microsomal vesicles of the insect cell-based system. The results indicate a stoichiometric incorporation of the azido amino acid at the desired position within the proteins. Moreover, the compatibility of cotranslational protein translocation, including glycosylation and amber suppression-based incorporation of p-azido-l-phenylalanine within a cell-free system, is demonstrated. The presented approach should be particularly useful for providing eukaryotic and membrane-associated proteins for investigation by fluorescence-based techniques.     

耐热性碱性磷酸酯酶作为非放射性标记物的研究

通过生物素与亲和素－酶复合物系统或地高辛与抗地高辛－酶复合物系统可把酶间接标记到探针上．Ｒｅｎｚ等通过不同的化学方法直接把酶标记到探针上［１～３］．耐热性碱性磷酸酯酶ＦＤ－ＴＡＰ（ｔｈｅｒｍｏｓｔａｂｌｅａｌｋａｌｉｎｅｐｈｏｓｐｈａｔａｓｅ）具有耐...     

The lactosylceramide binding specificity of Helicobacter pylori

The possible role of glycosphingolipids as adhesion receptors for the human gastric pathogen Helicobacter pylori was examined by use of radiolabeled bacteria, or protein extracts from the bacterial cell surface, in the thin-layer chromatogram binding assay. Of several binding specificities found, the binding to lactosylceramide is described in detail here, the others being reported elsewhere. By autoradiography a preferential binding to lactosylceramide having sphingosine/phytosphingosine and 2-D hydroxy fatty acids was detected, whereas lactosylceramide having sphingosine and nonhydroxy fatty acids was consistently nonbinding. A selective binding of H. pylori to lactosylceramide with phytosphingosine and 2-D hydroxy fatty acid was obtained when the different lactosylceramide species were incorporated into liposomes, but only in the presence of cholesterol, suggesting that this selectivity may be present also in vivo . Importantly, lactosylceramide with sphingosine and hydroxy fatty acids does not bind in this assay. Furthermore, a lactosylceramide-based binding pattern obtained for different trisaccharide glycosphingolipids is consistent with the assumption that this selectivity is due to binding of a conformation of lactosylceramide in which the oxygen of the 2-D fatty acid hydroxyl group forms a hydrogen bond with the Glc hydroxy methyl group, yielding an epitope presentation different from other possible conformers. An alternative conformation that may come into consideration corresponds to the crystal structure found for cerebroside, in which the fatty acid hydroxyl group is free to interact directly with the adhesin. By isolating glycosphingolipids from epithelial cells of human stomach from seven individuals, a binding of H.pylori to the diglycosylceramide region of the non-acid fraction could be demonstrated in one of these cases. Mass spectrometry showed that the binding-active sample contained diglycosylceramides with phytosphingosine and 2-D hydroxy fatty acids with 16-24 carbon atoms in agreement with the results related above.      

A practical method for cell-free protein synthesis to avoid stable isotope scrambling and dilution

During recent years, the targets of protein structure analysis using nuclear magnetic resonance spectroscopy have become larger and more complicated. As a result, a complete and precise stable isotope labeling technique has been desired. A cell-free protein synthesis system is appropriate for this purpose. In the current study, we achieved precise and complete ¹⁵N and ²H labeling using an Escherichia coli cell extract-based cell-free protein synthesis system by controlling the metabolic reactions in the system with their chemical inhibitors. The addition of aminooxyacetate, d-malate, l-methionine sulfoximine, S-methyl-l-cysteine sulfoximine, 6-diazo-5-oxo-l-norleucine, and 5-diazo-4-oxo-l-norvaline was quite effective for precise amino acid-selective ¹⁵N labeling even for aspartic acid, asparagine, glutamic acid, and glutamine, which generally suffer from severe isotope scrambling and dilution when using the conventional cell-free system. For ²H labeling, the back-protonation of the H^α and H^β positions, which commonly occurred in the conventional system, was dramatically suppressed by simply adding aminooxyacetate and d-malate to the cell-free system except for the H^α positions in methionine and cysteine.     

Fluorescent labeling of cell-free synthesized proteins by incorporation of fluorophore-conjugated nonnatural amino acids

Although fluorescent dyes, such as fluorescein derivatives, have bulky and complex structures, nonnatural amino acids carrying these fluorescein derivatives are acceptable by the Escherichia coli ribosome and are useful for the cotranslational fluorescent labeling of cell-free synthesized proteins. Surprisingly, the incorporation efficiency of nonnatural amino acids carrying fluorescein derivatives into translated proteins depends on the source of the translational machinery used in cell-free protein synthesis. That is, whereas the E. coli ribosome efficiently supported the incorporation of nonnatural amino acids carrying fluorescein derivatives into a protein structure, no detectable fluorescent signal was observed from the protein expressed in the eukaryotic cell-free protein synthesis system performed in the presence of fluorescein-conjugated aminoacylated transfer RNA (tRNA).     

cDNA cloning and expression of human lactosylceramide synthase

Lactosylceramide synthase is an enzyme that catalyzes the transfer of galactose from UDP-Gal to glucosylceramide, and thus participates in the biosynthesis of most glycolipids in mammals. We have isolated and sequenced the cDNA clone encoding human lactosylceramide synthase. The deduced amino acid sequence of the human lactosylceramide synthase showed 94.2% identity with rat lactosylceramide synthase. Northern blotting analysis revealed that lactosylceramide synthase mRNA was expressed in various tissues, with the highest level in brain and adrenal gland.     

Three-step preparation and purification of phosphorus-33-labeled creatine phosphate of high specific activity

Rabbit heart mitochondria were used as a source of enzymes for the synthesis of phosphoruslabeled creatine phosphate. This method is based on the coupled reaction between mitochondrial oxidative phosphorylation and mitochondrial-bound creatine kinase. It is possible to convert more than 90% of the inorganic phosphate (P_i) to creatine phosphate. The method used only small amounts of adenine nucleotides which led to a product with only slight nucleotide contamination. This could be removed by activated charcoal extraction. For further purification, a method for the removal of residual P_i is described.