Name: oligo mass profiling (olimp) of extracellular polysaccharides
Uploaded: 2010-06-20T17:00:00
Duration: 8 min 43 s
Description: Watch this Scientific Journal Video about OLIgo Mass Profiling OLIMP of Extracellular Polysaccharides at JoVE.com

This work was funded by the Energy Biosciences Institute's grant OO0G01.

The OLIMP method is exemplified on the major hemicellulose present in the cell walls of dicot plants, xyloglucan, using an endoglucanase as the glycosylhydrolase. The method is demonstrated with whole Arabidopsis seedlings as a plant tissue source. Enzyme and extracellular matrix material can be substituted depending on the desired analysis using the same procedure. 1. Cell wall isolation <ol> <li>Harvest five 5-day old whole Arabidopsis seedlings or the equivalent amount of your desired material and transfer them into a 1.5mL reaction tube. Make sure that the material is placed in the bottom of the tube.</li> <li>Add two 3mm metal balls to the reaction tube on top of the sample and snap-freeze in liquid nitrogen.</li> <li>Grind the frozen sample using a ball-mill (2:30min, 25Hz).</li> <li>Add 1mL 70% aqueous ethanol to the sample. Remove the metal balls using a magnet. Vortex thoroughly.</li> <li>Centrifuge sample at 14,000rpm for 10min to pellet the alcohol insoluble residue containing the cell wall material.</li> <li>Carefully remove the supernatant by aspiration. Make sure not to disturb the pellet. </li> <li>Add 1mL of chloroform/methanol (1:1 v/v) solution. Vortex thoroughly to resuspend the pellet.</li> <li>Centrifuge sample at 14,000rpm for 10 min and carefully remove the supernatant by aspiration. Make sure not to disturb the pellet.</li> <li>Dry the sample using a concentrator.</li> </ol> 2. Solubilization of oligosaccharides <ol> <li>For the solubilization the particular polysaccharide in form of its oligosaccharides resuspend the dry pellet in 25&mu;l of an appropriate buffer. For the endoglucanase 50mM Ammonium formate, pH4.5, is used. Add 0.2U of endoglucanase. Vortex the suspension and spin liquid down.</li> <li>Incubate the sample for 16h at 37&deg;C in an incubator, shaking at 300rpm.</li> <li>Remove the solvent of the digest (water) using a concentrator.</li> </ol> 3. MALDI-TOF analysis of the released oligosaccharides <ol> <li>BioRex MSZ 501 cation exchange resin beads are used to remove salts and enzyme from the digested sample. Condition the beads by placing an aliquot in an empty column and washing the beads with copious amounts of water.</li> <li>Add 5-10 BioRex beads to the digested and dried sample. Then add 10&mu;l water, for smaller amounts of material 5&mu;l of water may be used. Immerse the beads in the solution by briefly spinning the tube. Incubate for at least 10min at room temperature.</li> <li>Spot 2&mu;l matrix (2,5-dihydroxybenzoic acid (DHB), 10mg/ml in water) onto a MALDI target plate. Evaporate the matrix solvent under vacuum leading to homogenous matrix chemical crystals.</li> <li>Spot 2&mu;l of the desalted sample solution on top of the matrix crystals on the target plate. If you want to spot a large number of samples only keep on spotting for a maximum of 3min. This time-frame ensures that the first spotted sample is not dry yet. Wait for an additional 2min to ensure a thorough mixing of re-dissolved matrix and sample oligosaccharide molecules in the last spotted sample. Then dry the target plate under a vacuum. The sample/matrix mix should crystallize in less than 1min to enable homogenous crystallization.</li> <li>Place target plate into a MALDI-TOF mass spectrometer. The machine should be set to positive reflectron mode with an accelerating voltage of 20000V and a delay of 350 nm; the selected mass range should be 500-3000 Da (may change dependent on the expected oligomers). Start firing the laser and collect 100-200 spectra per sample, which are compiled to generate a representative average spectrum (Figure 2A). Ions representing specific oligosaccharides can be identified by their mass over charge (m/z) ratio. The ion intensities (peak height) of all ions of interest should be added up to 100% resulting in the relative abundance of each oligosaccharide in the sample (Figure 2B).</li> </ol> 4. In situ OLIMP analysis OLIMP can also be used directly on the tissue omitting any wall preparation steps. As an example etiolated hypocotyls of Arabidopsis as a plant tissue source are used. Again, an endoglucanase is used to determine the structure of the hemicelluloses xyloglucan. Enzyme and tissue material can be substituted depending on the desired analysis using the same procedure. <ol> <li>Harvest an etiolated seedling and place it onto an empty MALDI target plate and let the seedling dry.</li> <li>Add 0.5&mu;l endoglucanase (0.4U/&mu;l, dissolved in 50mM Ammonium formate, pH4.5) on the dried seedling at the desired position. Make sure that the enzyme drop touches partly the target plate. </li> <li>Place the MALDI target plate in a closed container with saturating humidity to avoid that the enzyme drop dries out. Incubate the plate in the chamber for 16h at 37&deg;C.</li> <li>Dry the MALDI target plate with the plant tissue and the enzyme drop under vacuum.</li> <li>Add 0.5&mu;l matrix (DHB; 10mg/l) on top of each dried enzyme spot. Let it stand for 2min.</li> <li>Dry the MALDI target plate under vacuum.</li> <li>Analyze samples with the MALDI-TOF. Place target plate with the tissue and the enzyme/matrix spot(s) into a MALDI-TOF mass spectrometer. The machine should be set to positive reflectron mode with an accelerating voltage of 20000V and a delay of 350 nm; the selected mass range should be 500-3000 Da (may change dependent on the expected oligomers).</li> <li>Start firing the laser onto the matrix/sample crystals NEXT to the tissue. Make sure you don't hit the tissue itself, as in such a case the time-of flight of the molecules will be off. Collect around 20-50 spectra per spot, which are compiled to generate a representative average spectrum (Figure 3). Ions representing specific oligosaccharides can be identified by their mass over charge (m/z) ratio. The ion intensities (ion height) can be reported and all ions of interest should be added up to 100% resulting in the relative abundance of each oligosaccharides in the sample.</li> </ol> 5. Representative Results An example of an OLIMP analysis of the hemicelluloses xyloglucan present in Arabidopsis seedlings is shown in Figure 2. Due to the mass differences of the ions and the known well characterized enzyme (endoglucanase) specificity the ions can be assigned to specific oligosaccharide structures (Figure 2A). Obviously, structural isomers cannot be distinguished. The basic assumption for the determination of the relative abundance of the various oligosaccharides (Figure 2B) is that their mass spec response factor is very similar for those oligosaccharides. As shown here, the OLIMP quantification is highly reproducible. However, please note that robustness of the method is highly dependent on the signal to noise ratios of the various oligosaccharide ions. For example contamination with salts or lower amounts of oligosaccharides can decrease that ratio. The OLIMP analysis on the tissue itself (in situ analysis) enables the study of very small and defined areas and involves very little sample preparation. In the example presented here (Figure 3) no qualitative (same ions) but quantitative differences (variation in the ion intensities) were observed between the shoot and root-tissue of the Arabidopsis seedling. Permutations of the OLIMP-method could thus lead to tissue "imaging". <img src="/files/ftp_upload/2046/2046fig1.jpg" alt="Figure 1" /> Figure 1. Flow chart of the OLIMP procedure using whole Arabidopsis seedlings as a plant source. First, the tissue is macerated and cell wall material is prepared (picture modified from Fujino et al.10). Then oligosaccharides of a particular wall polysaccharide are released using a specific hydrolase. Finally, the relative abundances of the soluble oligosaccharides are determined using MALDI-TOF mass spectrometry. <img src="/files/ftp_upload/2046/2046fig2.jpg" alt="Figure 2" /> Figure 2. Relative abundance of xyloglucan oligosaccharides in etiolated seedlings from Arabidopsis as determined by OLIMP. A) Representative xyloglucan oligosaccharide mass spectrum; each ion represents a specific oligosaccharide structure, structural isomers cannot be distinguished. B) Corresponding bar diagram for the determination of the relative oligosaccharide abundance. <img src="/files/ftp_upload/2046/2046fig3.jpg" alt="Figure 3" /> Figure 3. In situ OLIMP analysis using etiolated seedlings of Arabidopsis as example. Each enzyme/digestion droplet (colored circles) can be analyzed independently and a corresponding mass spectra can be obtained and analyzed. <img src="/files/ftp_upload/2046/2046fig4.jpg" alt="Figure 4" /> Figure 4. OLIMP spectrum of the hemicellulose xylan obtained by digesting Miscanthus leaf material with a xylanase (Megazyme).

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No conflicts of interest declared.

The OLIMP method presented here enables a very sensitive and rapid analysis of polymers present in the extracellular matrices. OLIMP combines the enzymatic release of oligomers with subsequent MALDI-TOF analysis. The generation of a MALDI-TOF spectrum takes less than one minute; hence OLIMP is suitable for a wide range of applications including high-throughput studies such as mutant screens. OLIMP is not restricted to plant polysaccharides but can potentially be applied to a wide range of polymers, only limited by the availability of specific hydrolytic enzymes. However, a limitation of OLIMP is that an absolute abundance of the polymer cannot be obtained. As mentioned before OLIMP can be used to study the structure of a variety of polysaccharides present in the extracellular matrix of a diversity of species. As an example, Figure 4 represents an OLIMP spectrum of the major hemicellulose in grass species, xylan. Here, cell wall material derived from the temperate grass Miscanthus was digested using a xylanase.

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		<th>Catalogue Number</th>
		<th>Comment</th>
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<td>2,5-dihydroxybenzoic acid</td>
<td>&nbsp;</td>
<td>Sigma-Aldrich</td>
<td>37550</td>
<td>10mg/mL in water</td>
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<td>BioRex MSZ 501(D) Resin</td>
<td>&nbsp;</td>
<td>BioRad</td>
<td>142-7425</td>
<td>&nbsp;</td>
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<td>Endoglucanase</td>
<td>&nbsp;</td>
<td>Megazyme</td>
<td>E-CELTR</td>
<td>&nbsp;</td>
<tr>
<td>Xylanase M6</td>
<td>&nbsp;</td>
<td>Megazyme</td>
<td>E-XYRU6</td>
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<td>Beat mill</td>
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<td>Kratos Analytical</td>
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<td>Vacuum manifold</td>
<td>&nbsp;</td>
<td>Millipore</td>
<td>MSVMHTS00</td>
<td>&nbsp;</td>
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<td>Vacuum pump</td>
<td>&nbsp;</td>
<td>Welch</td>
<td>DryFast Ultra 2032</td>
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oligo mass profiling (olimp) of extracellular polysaccharides

The direct contact of cells to the environment is mediated in many organisms by an extracellular matrix. One common aspect of extracellular matrices is that they contain complex sugar moieties in form of glycoproteins, proteoglycans, and/or polysaccharides. Examples include the extracellular matrix of humans and animal cells consisting mainly of fibrillar proteins and proteoglycans or the polysaccharide based cell walls of plants and fungi, and the proteoglycan/glycolipid based cell walls of bacteria. All these glycostructures play vital roles in cell-to-cell and cell-to-environment communication and signalling.
An extraordinary complex example of an extracellular matrix is present in the walls of higher plant cells. Their wall is made almost entirely of sugars, up to 75% dry weight, and consists of the most abundant biopolymers present on this planet. Therefore, research is conducted how to utilize these materials best as a carbon-neutral renewable resource to replace petrochemicals derived from fossil fuel. The main challenge for fuel conversion remains the recalcitrance of walls to enzymatic or chemical degradation due to the unique glycostructures present in this unique biocomposite.
Here, we present a method for the rapid and sensitive analysis of plant cell wall glycostructures. This method OLIgo Mass Profiling (OLIMP) is based the enzymatic release of oligosaccharides from wall materials facilitating specific glycosylhydrolases and subsequent analysis of the solubilized oligosaccharide mixtures using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS)1 (Figure 1). OLIMP requires walls of only 5000 cells for a complete analysis, can be performed on the tissue itself2, and is amenable to high-throughput analyses3. While the absolute amount of the solubilized oligosaccharides cannot be determined by OLIMP the relative abundance of the various oligosaccharide ions can be delineated from the mass spectra giving insights about the substitution-pattern of the native polysaccharide present in the wall.
OLIMP can be used to analyze a wide variety of wall polymers, limited only by the availability of specific enzymes4. For example, for the analysis of polymers present in the plant cell wall enzymes are available to analyse the hemicelluloses xyloglucan using a xyloglucanase5, 11, 12, 13, xylan using an endo-&beta;-(1-4)-xylanase 6,7, or for pectic polysaccharides using a combination of a polygalacturonase and a methylesterase 8. Furthermore, using the same principles of OLIMP glycosylhydrolase and even glycosyltransferase activities can be monitored and determined 9.

Watch this Scientific Journal Video about OLIgo Mass Profiling OLIMP of Extracellular Polysaccharides at JoVE.com

OLIgo Mass Profiling OLIMP of Extracellular Polysaccharides

A rapid way is described to gain insights into the structure of polysaccharides in an extracellular matrix. The method takes advantage of the specificity of glycosylhydrolases and the sensitivity of mass spectrometry allowing minute amounts of materials to be analyzed. This technique is adaptable to be used directly on tissue itself.

OLIgo Mass Profiling (OLIMP) of Extracellular Polysaccharides

The direct contact of cells to the environment is mediated in many organisms by an extracellular matrix. One common aspect of extracellular matrices is ...

oligo-mass-profiling-olimp-of-extracellular-polysaccharides

Research

JoVE Journal

Biology

MALDI Sample Preparation: the Ultra Thin Layer Method

This video demonstrates the preparation of an ultra-thin matrix/analyte layer for analyzing peptides and proteins by Matrix-Assisted Laser Desorption Ionization Mass Spectrometry (MALDI-MS) 1,2. The ultra-thin layer method involves the production of a substrate layer of matrix crystals (alpha-cyano-4-hydroxycinnamic acid) on the sample plate, which serves as a seeding ground for subsequent crystallization of a matrix/analyte mixture. Advantages of the ultra-thin layer method over other sample deposition approaches (e.g. dried droplet) are that it provides (i) greater tolerance to impurities such as salts and detergents, (ii) better resolution, and (iii) higher spatial uniformity. This method is especially useful for the accurate mass determination of proteins. The protocol was initially developed and optimized for the analysis of membrane proteins and used to successfully analyze ion channels, metabolite transporters, and receptors, containing between 2 and 12 transmembrane domains 2. Since the original publication, it has also shown to be equally useful for the analysis of soluble proteins. Indeed, we have used it for a large number of proteins having a wide range of properties, including those with molecular masses as high as 380 kDa 3. It is currently our method of choice for the molecular mass analysis of all proteins. The described procedure consistently produces high-quality spectra, and it is sensitive, robust, and easy to implement.

This video demonstrates the preparation of an ultra-thin matrix/analyte layer for analyzing peptides and proteins by Matrix-Assisted Laser Desorption Ionization Mass Spectrometry (MALDI-MS).

This video demonstrates the preparation of an ultra-thin matrix/analyte layer for analyzing peptides and proteins by Matrix-Assisted Laser Desorption ...

Antibody Profiling by Luciferase Immunoprecipitation Systems (LIPS)

Technologies for comprehensively understanding and quantifying antibody profiles to autoantigens and infectious agents may yield new insights into disease mechanisms and may elucidate new markers to substratify disease with different clinical features and better understand pathogenesis. We have developed a highly quantitative method called Luciferase Immunoprecipitation Systems (LIPS) for profiling patient sera antibody responses to autoantigens and pathogen antigens associated with infection. Unlike ELISAs, the highly sensitive LIPS is easily implemented to survey humoral serological response profiles to different antigens in a universal format and produces dynamic antibody titer ranges up to 6 log10 for some antigens. In these studies, quantitative profiling by LIPS of patient humoral responses against panels of antigens or even the entire proteome of some pathogens (i.e. HIV), is typically more informative than testing a single antigen by ELISA. In addition, LIPS also eliminates time and effort needed to produce highly purified antigens as well as the labor-intensive assay optimization steps needed for standard ELISAs. Here we provide a detailed protocol describing the technical aspects of performing LIPS assays for readily profiling antibody responses to single or multiple antigens.

Antibody Profiling by Luciferase Immunoprecipitation Systems LIPS

The technical aspects of performing LIPS (Luciferase Immunoprecipitation Systems) are described. The overall approach involves expressing chimeric genes encoding antigens fused to Renilla luciferase (Ruc) in mammalian cells. Crude Ruc-antigen extracts are then prepared and, without purification, employed in immunoprecipitation assays to quantify antibodies.

Technologies for comprehensively understanding and quantifying antibody profiles to autoantigens and infectious agents may yield new insights into disease ...

Profiling of Methyltransferases and Other S-adenosyl-L-homocysteine-binding Proteins by Capture Compound Mass Spectrometry (CCMS)

There is a variety of approaches to reduce the complexity of the proteome on the basis of functional small molecule-protein interactions such as affinity chromatography 1 or Activity Based Protein Profiling 2. Trifunctional Capture Compounds (CCs, Figure 1A) 3 are the basis for a generic approach, in which the initial equilibrium-driven interaction between a small molecule probe (the selectivity function, here S-adenosyl-L-homocysteine, SAH, Figure 1A) and target proteins is irreversibly fixed upon photo-crosslinking between an independent photo-activable reactivity function (here a phenylazide) of the CC and the surface of the target proteins. The sorting function (here biotin) serves to isolate the CC - protein conjugates from complex biological mixtures with the help of a solid phase (here streptavidin magnetic beads). Two configurations of the experiments are possible: "off-bead" 4 or the presently described "on-bead" configuration (Figure 1B). The selectivity function may be virtually any small molecule of interest (substrates, inhibitors, drug molecules).
S-Adenosyl-L-methionine (SAM, Figure 1A) is probably, second to ATP, the most widely used cofactor in nature 5, 6. It is used as the major methyl group donor in all living organisms with the chemical reaction being catalyzed by SAM-dependent methyltransferases (MTases), which methylate DNA 7, RNA 8, proteins 9, or small molecules 10. Given the crucial role of methylation reactions in diverse physiological scenarios (gene regulation, epigenetics, metabolism), the profiling of MTases can be expected to become of similar importance in functional proteomics as the profiling of kinases. Analytical tools for their profiling, however, have not been available. We recently introduced a CC with SAH as selectivity group to fill this technological gap (Figure 1A).
SAH, the product of SAM after methyl transfer, is a known general MTase product inhibitor 11. For this reason and because the natural cofactor SAM is used by further enzymes transferring other parts of the cofactor or initiating radical reactions as well as because of its chemical instability 12, SAH is an ideal selectivity function for a CC to target MTases. Here, we report the utility of the SAH-CC and CCMS by profiling MTases and other SAH-binding proteins from the strain DH5&alpha; of Escherichia coli (E. coli), one of the best-characterized prokaryotes, which has served as the preferred model organism in countless biochemical, biological, and biotechnological studies. Photo-activated crosslinking enhances yield and sensitivity of the experiment, and the specificity can be readily tested for in competition experiments using an excess of free SAH.

Profiling of Methyltransferases and Other S-adenosyl-L-homocysteine-binding Proteins by Capture Compound Mass Spectrometry CCMS

Capture Compounds are trifunctional small molecules to reduce the complexity of the proteome by functional reversible small molecule-protein interaction followed by photo-crosslinking and purification. Here we use a Capture Compound with S-adenosyl-L-homocysteine-binding as selectivity function to isolate methyltransferases from an Escherichia coli whole cell lysate and identify them by MS.

There is a variety of approaches to reduce the complexity of the proteome on the basis of functional small molecule-protein interactions such as affinity ...

Single Cell Transcriptional Profiling of Adult Mouse Cardiomyocytes

While numerous studies have examined gene expression changes from homogenates of heart tissue, this prevents studying the inherent stochastic variation between cells within a tissue. Isolation of pure cardiomyocyte populations through a collagenase perfusion of mouse hearts facilitates the generation of single cell microarrays for whole transcriptome gene expression, or qPCR of specific targets using nanofluidic arrays. We describe here a procedure to examine single cell gene expression profiles of cardiomyocytes isolated from the heart. This paradigm allows for the evaluation of metrics of interest which are not reliant on the mean (for example variance between cells within a tissue) which is not possible when using conventional whole tissue workflows for the evaluation of gene expression (Figure 1). We have achieved robust amplification of the single cell transcriptome yielding micrograms of double stranded cDNA that facilitates the use of microarrays on individual cells. In the procedure we describe the use of NimbleGen arrays which were selected for their ease of use and ability to customize their design. Alternatively, a reverse transcriptase - specific target amplification (RT-STA) reaction, allows for qPCR of hundreds of targets by nanofluidic PCR. Using either of these approaches, it is possible to examine the variability of expression between cells, as well as examining expression profiles of rare cell types from within a tissue. Overall, the single cell gene expression approach allows for the generation of data that can potentially identify idiosyncratic expression profiles that are typically averaged out when examining expression of millions of cells from typical homogenates generated from whole tissues.

Single cell expression profiling allows the detailed gene expression analysis of individual cells. We describe methods for the isolation of cardiomyocytes, and preparing the resulting lysates for either whole transcriptome microarray or qPCR of specific targets.

While numerous studies have examined gene expression changes from homogenates of heart tissue, this prevents studying the inherent stochastic variation ...

Profiling Thiol Redox Proteome Using Isotope Tagging Mass Spectrometry

Pseudomonas syringae pv. tomato strain DC3000 not only causes bacterial speck disease in Solanum lycopersicum but also on Brassica species, as well as on Arabidopsis thaliana, a genetically tractable host plant1,2. The accumulation of reactive oxygen species (ROS) in cotyledons inoculated with DC3000 indicates a role of ROS in modulating necrotic cell death during bacterial speck disease of tomato3. Hydrogen peroxide, a component of ROS, is produced after inoculation of tomato plants with Pseudomonas3. Hydrogen peroxide can be detected using a histochemical stain 3'-3' diaminobenzidine (DAB)4. DAB staining reacts with hydrogen peroxide to produce a brown stain on the leaf tissue4. ROS has a regulatory role of the cellular redox environment, which can change the redox status of certain proteins5. Cysteine is an important amino acid sensitive to redox changes. Under mild oxidation, reversible oxidation of cysteine sulfhydryl groups serves as redox sensors and signal transducers that regulate a variety of physiological processes6,7. Tandem mass tag (TMT) reagents enable concurrent identification and multiplexed quantitation of proteins in different samples using tandem mass spectrometry8,9. The cysteine-reactive TMT (cysTMT) reagents enable selective labeling and relative quantitation of cysteine-containing peptides from up to six biological samples. Each isobaric cysTMT tag has the same nominal parent mass and is composed of a sulfhydryl-reactive group, a MS-neutral spacer arm and an MS/MS reporter10. After labeling, the samples were subject to protease digestion. The cysteine-labeled peptides were enriched using a resin containing anti-TMT antibody. During MS/MS analysis, a series of reporter ions (i.e., 126-131 Da) emerge in the low mass region, providing information on relative quantitation. The workflow is effective for reducing sample complexity, improving dynamic range and studying cysteine modifications. Here we present redox proteomic analysis of the Pst DC3000 treated tomato (Rio Grande) leaves using cysTMT technology. This high-throughput method has the potential to be applied to studying other redox-regulated physiological processes.

Reactive oxygen species level is elevated when cells encounter stress conditions. Here we show the example of 3'-3' diaminobenzidine staining as well as cysTMT labeling and mass spectrometry to profile the redox proteome in Pseudomonas syringae treated tomato leaves.

Pseudomonas syringae pv. tomato strain DC3000 not only causes bacterial speck disease in Solanum lycopersicum but also on Brassica species, as well as on ...

Avidity-based Extracellular Interaction Screening (AVEXIS) for the Scalable Detection of Low-affinity Extracellular Receptor-Ligand Interactions

Extracellular protein:protein interactions between secreted or membrane-tethered proteins are critical for both initiating intercellular communication and ensuring cohesion within multicellular organisms. Proteins predicted to form extracellular interactions are encoded by approximately a quarter of human genes1, but despite their importance and abundance, the majority of these proteins have no documented binding partner. Primarily, this is due to their biochemical intractability: membrane-embedded proteins are difficult to solubilise in their native conformation and contain structurally-important posttranslational modifications. Also, the interaction affinities between receptor proteins are often characterised by extremely low interaction strengths (half-lives &lt; 1 second) precluding their detection with many commonly-used high throughput methods2. 
Here, we describe an assay, AVEXIS (AVidity-based EXtracellular Interaction Screen) that overcomes these technical challenges enabling the detection of very weak protein interactions (t1/2 &le; 0.1 sec) with a low false positive rate3. The assay is usually implemented in a high throughput format to enable the systematic screening of many thousands of interactions in a convenient microtitre plate format (Fig. 1). It relies on the production of soluble recombinant protein libraries that contain the ectodomain fragments of cell surface receptors or secreted proteins within which to screen for interactions; therefore, this approach is suitable for type I, type II, GPI-linked cell surface receptors and secreted proteins but not for multipass membrane proteins such as ion channels or transporters.
The recombinant protein libraries are produced using a convenient and high-level mammalian expression system4, to ensure that important posttranslational modifications such as glycosylation and disulphide bonds are added. Expressed recombinant proteins are secreted into the medium and produced in two forms: a biotinylated bait which can be captured on a streptavidin-coated solid phase suitable for screening, and a pentamerised enzyme-tagged (&beta;-lactamase) prey. The bait and prey proteins are presented to each other in a binary fashion to detect direct interactions between them, similar to a conventional ELISA (Fig. 1). The pentamerisation of the proteins in the prey is achieved through a peptide sequence from the cartilage oligomeric matrix protein (COMP) and increases the local concentration of the ectodomains thereby providing significant avidity gains to enable even very transient interactions to be detected. By normalising the activities of both the bait and prey to predetermined levels prior to screening, we have shown that interactions having monomeric half-lives of 0.1 sec can be detected with low false positive rates3.

Avidity-based Extracellular Interaction Screening AVEXIS for the Scalable Detection of Low-affinity Extracellular Receptor-Ligand Interactions

AVEXIS is a high throughput protein interaction assay developed to systematically screen for novel extracellular receptor-ligand pairs involved in cellular recognition processes. It is specifically designed to detect transient protein interactions that are difficult to identify using other high throughput approaches.

Extracellular protein:protein interactions between secreted or membrane-tethered proteins are critical for both initiating intercellular communication and ...

Glycan Profiling of Plant Cell Wall Polymers using Microarrays

Plant cell walls are complex matrixes of heterogeneous glycans which play an important role in the physiology and development of plants and provide the raw materials for human societies (e.g. wood, paper, textile and biofuel industries)1,2. However, understanding the biosynthesis and function of these components remains challenging.
Cell wall glycans are chemically and conformationally diverse due to the complexity of their building blocks, the glycosyl residues. These form linkages at multiple positions and differ in ring structure, isomeric or anomeric configuration, and in addition, are substituted with an array of non-sugar residues. Glycan composition varies in different cell and/or tissue types or even sub-domains of a single cell wall3. Furthermore, their composition is also modified during development1, or in response to environmental cues4.
In excess of 2,000 genes have Plant cell walls are complex matrixes of heterogeneous glycans been predicted to be involved in cell wall glycan biosynthesis and modification in Arabidopsis5. However, relatively few of the biosynthetic genes have been functionally characterized 4,5. Reverse genetics approaches are difficult because the genes are often differentially expressed, often at low levels, between cell types6. Also, mutant studies are often hindered by gene redundancy or compensatory mechanisms to ensure appropriate cell wall function is maintained7. Thus novel approaches are needed to rapidly characterise the diverse range of glycan structures and to facilitate functional genomics approaches to understanding cell wall biosynthesis and modification.
Monoclonal antibodies (mAbs)8,9 have emerged as an important tool for determining glycan structure and distribution in plants. These recognise distinct epitopes present within major classes of plant cell wall glycans, including pectins, xyloglucans, xylans, mannans, glucans and arabinogalactans. Recently their use has been extended to large-scale screening experiments to determine the relative abundance of glycans in a broad range of plant and tissue types simultaneously9,10,11.
Here we present a microarray-based glycan screening method called Comprehensive Microarray Polymer Profiling (CoMPP) (Figures 1 &amp; 2)10,11 that enables multiple samples (100 sec) to be screened using a miniaturised microarray platform with reduced reagent and sample volumes. The spot signals on the microarray can be formally quantified to give semi-quantitative data about glycan epitope occurrence. This approach is well suited to tracking glycan changes in complex biological systems12 and providing a global overview of cell wall composition particularly when prior knowledge of this is unavailable.

A technique called Comprehensive Microarray Polymer Profiling (CoMPP) for the characterisation of plant cell wall glycans is described. This method combines the specificity of monoclonal antibodies directed to defined glycan-epitopes with a miniature microarray analytical platform allowing screening of glycan occurrence in a broad range of biological contexts.

Plant cell walls are complex matrixes of heterogeneous glycans which play an important role in the physiology and development of plants and provide the ...

Analysis of Translation Initiation During Stress Conditions by Polysome Profiling

Precise control of mRNA translation is fundamental for eukaryotic cell homeostasis, particularly in response to physiological and pathological stress. Alterations of this program can lead to the growth of damaged cells, a hallmark of cancer development, or to premature cell death such as seen in neurodegenerative diseases. Much of what is known concerning the molecular basis for translational control has been obtained from polysome analysis using a density gradient fractionation system. This technique relies on ultracentrifugation of cytoplasmic extracts on a linear sucrose gradient. Once the spin is completed, the system allows fractionation and quantification of centrifuged zones corresponding to different translating ribosomes populations, thus resulting in a polysome profile. Changes in the polysome profile are indicative of changes or defects in translation initiation that occur in response to various types of stress. This technique also allows to assess the role of specific proteins on translation initiation, and to measure translational activity of specific mRNAs. Here we describe our protocol to perform polysome profiles in order to assess translation initiation of eukaryotic cells and tissues under either normal or stress growth conditions.

Here, we describe a method to analyze changes in the initiation of mRNA translation of eukaryotic cells in response to stress conditions. This method is based on the velocity separation on sucrose gradients of translating ribosomes from non-translating ribosomes.

Precise control of mRNA translation is fundamental for eukaryotic cell homeostasis, particularly in response to physiological and pathological stress. ...

Enrichment of Extracellular Matrix Proteins from Tissues and Digestion into Peptides for Mass Spectrometry Analysis

The extracellular matrix (ECM) is a complex meshwork of cross-linked proteins that provides biophysical and biochemical cues that are major regulators of cell proliferation, survival, migration, etc. The ECM plays important roles in development and in diverse pathologies including cardio-vascular and musculo-skeletal diseases, fibrosis, and cancer. Thus, characterizing the composition of ECMs of normal and diseased tissues could lead to the identification of novel prognostic and diagnostic biomarkers and potential novel therapeutic targets. However, the very nature of ECM proteins (large in size, cross-linked and covalently bound, heavily glycosylated) has rendered biochemical analyses of ECMs challenging. To overcome this challenge, we developed a method to enrich ECMs from fresh or frozen tissues and tumors that takes advantage of the insolubility of ECM proteins. We describe here in detail the decellularization procedure that consists of sequential incubations in buffers of different pH and salt and detergent concentrations and that results in 1) the extraction of intracellular (cytosolic, nuclear, membrane and cytoskeletal) proteins and 2) the enrichment of ECM proteins. We then describe how to deglycosylate and digest ECM-enriched protein preparations into peptides for subsequent analysis by mass spectrometry.

This protocol describes a procedure for enriching ECM proteins from tissues or tumors and deglycosylating and digesting the ECM-enriched preparations into peptides to analyze their protein composition by mass spectrometry.

The extracellular matrix (ECM) is a complex meshwork of cross-linked proteins that provides biophysical and biochemical cues that are major regulators of ...

Cellular Redox Profiling Using High-content Microscopy

Reactive oxygen species (ROS) regulate essential cellular processes including gene expression, migration, differentiation and proliferation. However, excessive ROS levels induce a state of oxidative stress, which is accompanied by irreversible oxidative damage to DNA, lipids and proteins. Thus, quantification of ROS provides a direct proxy for cellular health condition. Since mitochondria are among the major cellular sources and targets of ROS, joint analysis of mitochondrial function and ROS production in the same cells is crucial for better understanding the interconnection in pathophysiological conditions. Therefore, a high-content microscopy-based strategy was developed for simultaneous quantification of intracellular ROS levels, mitochondrial membrane potential (&#916;&#936;m) and mitochondrial morphology. It is based on automated widefield fluorescence microscopy and image analysis of living adherent cells, grown in multi-well plates, and stained with the cell-permeable fluorescent reporter molecules CM-H2DCFDA (ROS) and TMRM (&#916;&#936;m and mitochondrial morphology). In contrast with fluorimetry or flow-cytometry, this strategy allows quantification of subcellular parameters at the level of the individual cell with high spatiotemporal resolution, both before and after experimental stimulation. Importantly, the image-based nature of the method allows extracting morphological parameters in addition to signal intensities. The combined feature set is used for explorative and statistical multivariate data analysis to detect differences between subpopulations, cell types and/or treatments. Here, a detailed description of the assay is provided, along with an example experiment that proves its potential for unambiguous discrimination between cellular states after chemical perturbation.

This paper presents a high-content microscopy workflow for simultaneous quantification of intracellular ROS levels, as well as mitochondrial membrane potential and morphology &#8211; jointly referred to as mitochondrial morphofunction &#8211; in living adherent cells using the cell-permeant fluorescent reporter molecules 5-(and-6)-chloromethyl-2&#39;,7&#39;-dichlorodihydrofluorescein diacetate, acetyl ester (CM-H2DCFDA) and tetramethylrhodamine methylester (TMRM).

Reactive oxygen species (ROS) regulate essential cellular processes including gene expression, migration, differentiation and proliferation. However, ...