Thin-layer chromatography blotting using polyvinylidene difluoride membrane (far-eastern blotting) and its applications

Streamlining assays of glycosyltransferases activity using in vitro GT-array (i-GT-ray) platform: Application to family GT37 fucosyltransferases

Numerous putative glycosyltransferases (GTs) have been identified using bioinformatic approaches. However, demonstrating the activity of these GTs remains a challenge. Here, we describe the development of a rapid in vitro GT-array screening platform for activity of GTs. GT-arrays are generated by cell-free in vitro protein synthesis and binding using microplates precoated with a N-terminal Halo- or a C-terminal GST-tagged GT-encoding plasmid DNA and a capture antibody. These arrays are then used for screening of transferase activities and the reactions are monitored by a luminescence GLO assay. The products formed by these reactions can be analyzed directly from the microplates by mass spectrometry. Using this platform, a total of 280 assays were performed to screen 22 putative fucosyltransferases (FUTs) from family GT37 (seven from Arabidopsis and 15 from rice) for activity toward five acceptors: non-fucosylated tamarind xyloglucan (TXyG), arabinotriose (Ara3), non-fucosylated rhamnogalacturonan I (RG-I), and RG-II from the mur1-1 Arabidopsis mutant, and the celery RG-II monomer lacking Arap and MeFuc of chain B and l-Gal of chain A. Our screen showed that AtFUT2, AtFUT5, and AtFUT10 have activity toward RG-I, while AtFUT8 was active on RG-II. Five rice OsFUTs have XyG-FUT activity and four rice OsFUTs have activity toward Ara3. None of the putative OsFUTs were active on the RG-I and RG-II. However, promiscuity toward acceptors was observed for several FUTs. These findings extend our knowledge of cell wall polysaccharide fucosylation in plants. We believe that in vitro GT-array platform provides a valuable tool for cell wall biochemistry and other research fields.

Unique gangliosides synthesized in vitro by sialyltransferases from marine bacteria and their characterization: ganglioside synthesis by bacterial sialyltransferases

On the basis of the results outlined in our previous report, bacterial sialyltransferases (ST) from marine sources were further characterized using glycosphingolipids (GSL), especially ganglio-series GSLs, based on the enzymatic characteristics and kinetic parameters obtained by Line weaver-Burk plots. Among them, GA1 and GA2 were found to be good substrates for these unique STs. Thus, new gangliosides synthesized by α2-3 and α2-6STs were structurally characterized by several analytical procedures. The ganglioside generated by the catalytic activity of α2-3ST was identified as GM1b. On the other hand, when enzyme reactions by α2-6STs were performed using substrates GA2 and GA1, very unique gangliosides were generated. The structures were identified as NeuAcα2-6GalNAcβ1-4Galβ1-4Glcβ-Cer and NeuAcα2-6Galβ1-3GalNAcβ1-4Galβ1-4Glcβ-Cer, respectively. The synthesized ganglioside NeuAcα2-6GalNAcβ1-4Galβ1-4Glcβ-Cer showed binding activity to the influenza A virus {A/Panama/2007/99 (H3N2)} at a similar level to purified sialyl(α2-3)paragloboside (S2-3PG) and sialyl(α2-6)paragloboside (S2-6PG) from mammalian sources. The evidence suggests that these STs have unique features, including substrate specificities restricted not only to lacto-series but also to ganglio-series GSLs, as well as catalytic potentials for ganglioside synthesis. This evidence demonstrates that effective in vitro ganglioside synthesis could be a valuable tool for selectively synthesizing sialic acid (Sia) modifications, thereby preparing large-scale gangliosides and permitting the exploration of unknown functions.

Structure-function analysis of endogenous lectin mind-the-gap in synaptogenesis

Mind-the-Gap (MTG) is required for neuronal induction of Drosophila neuromuscular junction (NMJ) postsynaptic domains, including glutamate receptor (GluR) localization. We have previously hypothesized that MTG is secreted from the presynaptic terminal to reside in the synaptic cleft, where it binds glycans to organize the heavily glycosylated, extracellular synaptomatrix required for transsynaptic signaling between neuron and muscle. In this study, we test this hypothesis with MTG structure-function analyses of predicted signal peptide (SP) and carbohydrate-binding domain (CBD), by introducing deletion and point-mutant transgenic constructs into mtg null mutants. We show that the SP is required for MTG secretion and localization to synapses in vivo. We further show that the CBD is required to restrict MTG diffusion in the extracellular synaptomatrix and for postembryonic viability. However, CBD mutation results in elevation of postsynaptic GluR localization during synaptogenesis, not the mtg null mutant phenotype of reduced GluRs as predicted by our hypothesis, suggesting that proper synaptic localization of MTG limits GluR recruitment. In further testing CBD requirements, we show that MTG binds N-acetylglucosamine (GlcNAc) in a Ca(2+)-dependent manner, and thereby binds HRP-epitope glycans, but that these carbohydrate interactions do not require the CBD. We conclude that the MTG lectin has both positive and negative binding interactions with glycans in the extracellular synaptic domain, which both facilitate and limit GluR localization during NMJ embryonic synaptogenesis.

Production and characterization of monoclonal antibodies specific to lactotriaosylceramide

We have established hybridoma cell lines producing monoclonal antibodies (mAbs) directed to N-acetylglucosaminylβ1-3galactose (GlcNAcβ1-3Gal) residue by immunizing BALB/c mice with lactotriaosylceramide (Lc(3)Cer). These obtained hybridoma cells, specific to Lc(3)Cer, were dual immunoglobulin (Ig)-producing cells which secreted both IgM and IgG molecules as antibodies. The established mAbs are able to react with not only Lc(3)Cer but also GlcNAcβ1-3-terminal glycosphingolipids (GSLs) despite branching or lactosamine chain lengths and human transferrin with terminal GlcNAc residues. Comparison of the variable regions of the cloned IgM and IgG by reversed transcription-polymerase chain reaction analysis confirmed that the variable regions determine the specificity, the other amino acids are conserved, and these mAbs are encoded by J558 and Vκ-21family genes. Furthermore, we have analyzed the expression of GSLs with GlcNAcβ1-3 epitope in acute leukemia cell lines and mouse fetal tissues using these mAbs, in which antigens were distributed comparatively. These mAbs are useful for studying the precise distribution of GlcNAcβ1-3Gal-terminating GSL expression in tissues as well as for detecting GSLs carrying terminal GlcNAcβ1-3Gal carbohydrate structure.

Advances on the compositional analysis of glycosphingolipids combining thin-layer chromatography with mass spectrometry

Glycosphingolipids (GSLs), composed of a hydrophilic carbohydrate chain and a lipophilic ceramide anchor, play pivotal roles in countless biological processes, including infectious diseases and the development of cancer. Knowledge of the number and sequence of monosaccharides and their anomeric configuration and linkage type, which make up the principal items of the glyco code of biologically active carbohydrate chains, is essential for exploring the function of GSLs. As part of the investigation of the vertebrate glycome, GSL analysis is undergoing rapid expansion owing to the application of novel biochemical and biophysical technologies. Mass spectrometry (MS) takes part in the network of collaborations to further unravel structural and functional aspects within the fascinating world of GSLs with the ultimate aim to better define their role in human health and disease. However, a single-method analytical MS technique without supporting tools is limited yielding only partial structural information. Because of its superior resolving power, robustness, and easy handling, high-performance thin-layer chromatography (TLC) is widely used as an invaluable tool in GSL analysis. The intention of this review is to give an insight into current advances obtained by coupling supplementary techniques such as TLC and mass spectrometry. A retrospective view of the development of this concept and the recent improvements by merging (1) TLC separation of GSLs, (2) their detection with oligosaccharide-specific proteins, and (3) in situ MS analysis of protein-detected GSLs directly on the TLC plate, are provided. The procedure works on a nanogram scale and was successfully applied to the identification of cancer-associated GSLs in several types of human tumors. The combination of these two supplementary techniques opens new doors by delivering specific structural information of trace quantities of GSLs with only limited investment in sample preparation.

Sialyltransferases of marine bacteria efficiently utilize glycosphingolipid substrates

Bacterial sialyltransferases (STs) from marine sources were characterized using glycosphingolipids (GSLs). Bacterial STs were found to be beta-galacotoside STs. There were two types of STs: (1) ST obtained from strains such as ishi-224, 05JTC1 (#1), ishi-467, 05JTD2 (#2), and faj-16, 05JTE1 (#3), which form alpha2-3 sialic acid (Sia) linkages, named alpha2-3ST, (2) ST obtained from strains such as ISH-224, N1C0 (#4), pda-rec, 05JTB2 (#5), and pda-0160, 05JTA2 (#6), which form alpha2-6 Sia linkages, named alpha2-6ST. All STs showed affinity to neolacto- and lacto-series GSLs, particularly in neolactotetraosyl ceramide (nLc(4)Cer). No large differences were observed in the pH and temperature profiles of enzyme activities. Kinetic parameters obtained by Lineweaver-Burk plot analysis showed that #3 and #4 STs had practical synthetic activity and thus it became easily possible to achieve large-scale ganglioside synthesis (100-300 muM) using these recombinant enzymes. Gangliosides synthesized from nLc(4)Cer by alpha2-3 and alpha2-6STs were structurally characterized by several analytical and immunological methods, and they were identified as IV(3)alphaNeuAc-nLc(4)Cer(S2-3PG) and IV(6)alphaNeuAc-nLc(4)Cer (S2-6PG), respectively. Further characterization of these STs using lactotetraosylceramide (Lc(4)Cer), neolactohexaosylceramide (i antigen), and IV(6)kladoLc(8)Cer (I antigen) showed the synthesis of corresponding gangliosides as well. Synthesized gangliosides showed binding activity to the influenza A virus [A/panama/2007/99 (H3N2)] at a similar level to purified S2-3PG and S2-6PG from mammalian sources. The above evidence suggests that these STs have unique features, including substrate specificities restricted to lacto- and neolactoseries GSLs, as well as catalytic potentials for ganglioside synthesis. This demonstrates that efficient in vitro ganglioside synthesis could be a valuable tool for selectively synthesizing Sias modifications, thereby permitting the exploration of unknown functions.

High-sensitivity analysis of glycosphingolipids by matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight imaging mass spectrometry on transfer membranes

Glycosphingolipids are ubiquitous constituents of cells. Yet there is still room for improvement in the techniques for analyzing glycosphingolipids. Here we report our highly sensitive and convenient analytical technology with imaging mass spectrometry for detailed structural analysis of glycosphingolipids. We were able to determine detailed ceramide structures; i.e., both the sphingosine base and fatty acid, by MS/MS/MS analysis on a PVDF membrane with 10 pmol of GM1, with which only faint bands were visible by primuline staining. The limit of detection was approximately 1 pmol of GM1, which is lower than the value in the conventional reports (10 pmol).

Analyzing phosphoinositides and their interacting proteins

Phosphorylated derivatives of phosphatidylinositol (PtdIns), known as phosphoinositides (PIs), are essential regulators of nuclear functions, cytoskeletal dynamics, cell signaling and membrane trafficking. These lipids are found on the cytosolic face of intracellular membranes but can also be detected in membrane-free regions of the nucleoplasm. Their downstream effectors include several proteins that contain various PI-specific domains. Because impaired PI metabolism is associated with disorders such as cancer, cardiovascular disease and immune dysfunction, there is currently great interest in studying PIs and their metabolic enzymes. Here we describe strategies and techniques for quantitative and qualitative measurement of PIs, for characterization of specific PI-binding proteins and for determination of PI kinase and phosphatase activities in vitro and in vivo.

Thin Layer Chromatography–Blotting, a Novel Method for the Detection of Phosphoinositides

Phosphoinositides are believed to be involved in fundamental cellular events such as signal transduction and vesicular trafficking. Aberrant metabolisms of this lipid, caused by mutations in phosphoinositide kinases, phosphatases and lipases are known to be related to variety of human disorders such as diabetes and cancer. While the majority of such information is obtained by analyzing genetic and biochemical properties of phosphoinositide-metabolic enzymes, direct measurement of cellular content of the lipid is hindered by the lack of a simple method that is sensitive enough to measure phosphoinositides present in trace amounts in vivo. Here, we describe a novel, thin layer chromatography (TLC)-based method by which cellular phosphoinositides are separated, transferred and detected by specific phosphoinositide-binding domains. This method was applied to follow the generation of minor phosphoinositides, such as PtdIns(3,4,5)P3 and PtdIns(3,4)P2 in response to insulin and to compare PtdIns(4,5)P2 and PtdIns(3,4,5)P3 levels in several cancer cell lines. The method has potential application not only in investigating the physiological roles of phosphoinositides, but also in diagnosing metabolic disease and cancer by directly assessing phosphoinositide levels in samples obtained from patients.

Simple Synthesis of Deuterium and 13C Labeled Trifluoromethyl Phenyldiazirine Derivatives as Stable Isotope Tags for Mass Spectrometry

The synthesis of trifluoromethyl diazirine with a stable isotope tag is reported. We found that both Friedel-Crafts acylation and reduction of aryl carbonyl to methylene, using commercially available stable-isotope reagents, were utilized for the synthesis of diazirinyl fatty acid derivatives. The stable isotope labeled diazirine may be valuable for identifying binding sites by mass spectrometry.

Gangliosides with O-acetylated sialic acids in tumors of neuroectodermal origin

Gangliosides, carrying an O-acetylated sialic acid in their carbohydrate moiety, are often found in growing and developing tissues, especially of neuro-ectodermal origin. The most prominent one is 9-O-Ac-GD3, which is considered as an oncofetal marker in animal and human tumors like neuronal tumors, melanoma, basalioma or breast cancer, as well as in psoriatic lesions. Also other gangliosides like GD2 or GT3 were found to be O-acetylated in their terminal sialic acid. In this review we are summarising the occurrence of such gangliosides in normal and transformed tissues and delineate a more general theory that O-acetylated sialic acids in gangliosides are a universal marker for growing cells and tissues.

Versatile synthesis of phenoxydiazirine-based fatty acid analogues and photoreactive galactosylceramide

A versatile synthesis of diazirine-based photoreactive fatty acid analogues is reported. The key step is phenoxy alkylation of diazirine with halo alkyl acid esters. The conditions described will be acceptable for the synthesis of various alkyl-length derivatives. The fatty acid derivatives are acceptors for reverse reactions of sphingolipid ceramide N-deacylase (SCDase), which catalyzes the condensation of psychosine and fatty acids to form photoreactive galactosylceramide. The photoreactive galactosylceramide can also be prepared with chemical synthesis, condensation of psychosine and fatty acid succinimidyl ester, and is recognized with anti-GarCer antibody both before and after irradiation.

Structure of the main ganglioside from the brain of Xenopus laevis

The main component of the ganglioside(1) mixture from the brain of the adult amphibian Xenopus laevis accounts for 35% of the total, as lipid bound sialic acid. This ganglioside has been purified and characterized by thin layer chromatography, partial and exhaustive enzymatic hydrolysis with sialidase, TLC-overlay procedures with anti-Gg(4)Cer and anti-Neu5Acalpha6GalNAcbeta specific monoclonal antibodies and mass spectrometry. All together the results suggest the following structure: Neu5Acalpha8Neu5Acalpha3Galbeta3(Neu5Acalpha8Neu5Acalpha6)GalNAcbeta4Galbeta4Glcbeta1Cer, or, IV(3)-alpha-Neu5Ac(2),III(6)-alpha-Neu5Ac(2)-Gg(4)Cer.