Comparison of methods of immobilization to enzyme-linked immunosorbent assay plates for the detection of sugar chains

Solid-phase glycan isolation for glycomics analysis

Glycosylation is one of the most significant protein PTMs. The biological activities of proteins are dramatically changed by the glycans associated with them. Thus, structural analysis of the glycans of glycoproteins in complex biological or clinical samples is critical in correlation with the functions of glycans with diseases. Profiling of glycans by HPLC-MS is a commonly used technique in analyzing glycan structures and quantifying their relative abundance in different biological systems. Methods relied on MS require isolation of glycans from negligible salts and other contaminant ions since salts and ions may interfere with the glycans, resulting in poor glycan ionization. To accomplish those objectives, glycan isolation and clean-up methods including SPE, liquid-phase extraction, chromatography, and electrophoresis have been developed. Traditionally, glycans are isolated from proteins or peptides using a combination of hydrophobic and hydrophilic columns: proteins and peptides remain on hydrophobic absorbent while glycans, salts, and other hydrophilic reagents are collected as flowthrough. The glycans in the flowthrough are then purified through graphite-activated carbon column by hydrophilic interaction LC. Yet, the drawback in these affinity-based approaches is nonspecific binding. As a result, chemical methods by hydrazide or oxime have been developed for solid-phase isolation of glycans with high specificity and yield. Combined with high-resolution MS, specific glycan isolation techniques provide tremendous potentials as useful tools for glycomics analysis.

Carbohydrate microarrays in 96-well polystyrene microtiter plates

A method for the preparation of carbohydrate microarrays inside 96-well polystyrene microtiter plates is described. The key step in this strategy represents the synthesis of carbohydrate-dextran conjugates by copper (I)-catalyzed [3 + 2] cycloaddition between alkyne carbohydrate derivative and a specially designed azido dextran polymer. The conjugates adsorb efficiently on polystyrene surface and can be printed inside 96-well plates using a non-contact piezoelectric microarrayer. Model interactions with a selection of lectins (concanavalin A, wheat germ agglutinin, Erythrina Cristagalli) display the efficiency of the immobilization method, its reproducibility and the specificity of biomolecular interactions occurring at the polystyrene-water interface.

Development of a sensitive and reliable ELISA for quantification of wheat germ agglutinin

Among others, lectin-mediated drug delivery is currently discussed as a promising strategy towards improved bioavailability of biotech drugs. For quantitative determination of the lectin from wheat germ (WGA), a sandwich ELISA relying on capture of the lectin by pig gastric mucin coated wells and detection of bound WGA by a lectin specific first antibody followed by peroxidase-labelled second antibody was elaborated. The stepwise optimised protocol allows quantification over the range from 10 to 1000 ng/ml WGA with a coefficient of determination of 0.9991. The day to day variation was +/-0.09 OD at 500 ng/ml WGA. Additionally, the presented ELISA-protocol allows determination of WGA in serum with the same sensitivity and reliability as in buffer. Lectins with different carbohydrate specificity such as those from jack beans and peanuts exhibited no cross-reactivity. Among the lectins with the same carbohydrate specificity that from potatoes interfered with the assay, whereas that from tomatoes was not recognised by the first antibody. Since the potato lectin is fully degraded in the intestine, no cross-reactivity with WGA is expected in serum samples. Following on from these results, the absorption rate of WGA in biologically active form might be determined as a basis for further steps towards improved drug delivery systems.

Solid-phase chemical tools for glycobiology

Techniques involving solid supports have played crucial roles in the development of genomics, proteomics, and in molecular biology in general. Similarly, methods for immobilization or attachment to surfaces and resins have become ubiquitous in sequencing, synthesis, analysis, and screening of oligonucleotides, peptides, and proteins. However, solid-phase tools have been employed to a much lesser extent in glycobiology and glycomics. This review provides a comprehensive overview of solid-phase chemical tools for glycobiology including methodologies and applications. We provide a broad perspective of different approaches, including some well-established ones, such as immobilization in microtiter plates and to cross-linked polymers. Emerging areas such as glycan microarrays and glycan sequencing, quantum dots, and gold nanoparticles for nanobioscience applications are also discussed. The applications reviewed here include enzymology, immunology, elucidation of biosynthesis, and systems biology, as well as first steps toward solid-supported sequencing. From these methods and applications emerge a general vision for the use of solid-phase chemical tools in glycobiology.

Oligosaccharide microarrays fabricated on aminooxyacetyl functionalized glass surface for characterization of carbohydrate–protein interaction

Carbohydrate-protein interactions play important biological roles in biological processes. But there is a lack of high-throughput methods to elucidate recognition events between carbohydrates and proteins. This paper reported a convenient and efficient method for preparing oligosaccharide microarrays, wherein the underivatized oligosaccharide probes were efficiently immobilized on aminooxyacetyl functionalized glass surface by formation of oxime bonding with the carbonyl group at the reducing end of the suitable carbohydrates via irreversible condensation. Prototypes of carbohydrate microarrays containing 10 oligosaccharides were fabricated on aminooxyacetyl functionalized glass by robotic arrayer. Utilization of the prepared carbohydrate microarrays for the characterization of carbohydrate-protein interaction reveals that carbohydrates with different structural features selectively bound to the corresponding lectins with relative binding affinities that correlated with those obtained from solution-based assays. The limit of detection (LOD) for lectin ConA on the fabricated carbohydrate microarrays was determined to be approximately 0.008 microg/mL. Inhibition experiment with soluble carbohydrates also demonstrated that the binding affinities of lectins to different carbohydrates could be analyzed quantitatively by determining IC(50) values of the soluble carbohydrates with the carbohydrate microarrays. This work provides a simple procedure to prepare carbohydrate microarray for high-throughput parallel characterization of carbohydrate-protein interaction.

High molecular weight neoglycoconjugates for solid phase assays

Adsorption of a carbohydrate on solid phase is the necessary stage of the immunosorbent assay (ELISA) and analogous methods of the study of carbohydrate-protein interaction. Usually physical adsorption on polystyrene requires a high concentration of conjugated carbohydrate and, thus, enormous consumption of it. In this study, we explored two approaches allowing more rational use of oligosaccharide (Glyc). The first of them is based on the covalent immobilization of neoglycoconjugates on the NH(2)-modified polystyrene; the second one is based on the elevated adherence of high m.w. neoglycoconjugates to polystyrene. Covalent immobilization of polyacrylamide conjugates, Glyc-PAA, provided a possibility to solve the problem, but the nonspecific binding of antibodies in ELISA proved to be unacceptably high. At the same time, the increase of the Glyc-PAA m.w. from 30 kDa to 2,000 kDa allowed a 10-20 fold decrease of its consumption, when using physical adsorption, whereas the assay background remained at the low level. The amount of 2,000 kDa Glyc-PAA that is sufficient for the coating of a standard 96-well plate corresponds to the nanomole level of oligosaccharide, this providing a possibility to use saccharides that are available in a very limited amount when studying the carbohydrate-protein interaction with solid-phase techniques.

High-throughput methods for measuring heparanase activity and screening potential antimetastatic and anti-inflammatory agents

Heparanase plays an important role in the degradation of the extracellular matrix. It is implicated in inflammation, tumor angiogenesis and metastasis. We have developed two high-throughput methods for measuring heparanase activity and screening potential inhibitors. The first method involves coating fibroblast growth factor (FGF) on microtiter plates and capturing fluorescein isothiocyanate (FITC)-labeled heparin sulfate (HS), which is used as a substrate for heparanase digestion. Labeled HS fragments are released into the medium and quantitated by fluorescence intensity measurement. We have implemented this assay method into a Zeiss uHTS system and screened compound libraries for heparanase inhibitors. The second method involves labeling HS with biotin followed by FITC to generate a dual-labeled HS. The labeled material is bound to streptavidin-coated plates and used as a substrate for heparanase digestion. Both methods are sensitive and easily applicable to robotic systems. In addition, we have labeled both HS and biotin-HS with Eu-chelate, a fluorophore that exhibits long decay fluorescence. Assays using Eu-labeled HS and Eu-labeled biotin-HS have been developed and show higher sensitivity than those using FITC-labeled material. Furthermore, assays using Eu-chelate HS (or biotin-HS) should eliminate the interference of fluorescence compounds.