Sugar-lectin interactions investigated through affinity capillary electrophoresis

Clinical and pharmaceutical applications of affinity ligands in capillary electrophoresis: A review

Affinity capillary electrophoresis (ACE) is a separation technique that combines a biologically-related binding agent with the separating power and efficiency of capillary electrophoresis. This review will examine several classes of binding agents that have been used in ACE and applications that have been described for the resulting methods in clinical or pharmaceutical analysis. Binding agents that will be considered are antibodies, aptamers, lectins, serum proteins, carbohydrates, and enzymes. This review will also describe the various formats in which each type of binding agent has been used in CE, including both homogeneous and heterogeneous methods. Specific areas of applications that will be considered are CE-based immunoassays, glycoprotein/glycan separations, chiral separations, and biointeraction studies. The general principles and formats of ACE for each of these applications will be examined, along with the potential advantages or limitations of these methods.

Radiolabeling of cramoll 1,4: evaluation of the biodistribution

The cramoll 1,4 is a well-studied lectin. However, few studies about its biodistribution have been done before. In this study, we radiolabeled the cramol 1,4 with Tc-99m and analyzed the biodistribution. The results showed that the cramol has an abnormal uptake by the bowel with reflections on its clearance mechanism.

Potential effects of Cramoll 1,4 lectin on murine Schistosomiasis mansoni

Cratylia mollis is a natural forage plant from the Northeast of Brazil. C. mollis seed lectin (Cramoll) containing molecular forms 1 and 4 (Cramoll 1,4) has shown anti-inflammatory and wound-healing activities. This work analyzed the effect of Cramoll 1,4 on experimental schistosomiasis in mice. Experimental groups (n=15/group) were composed of female albino Swiss mice, which were subcutaneously and caudally infected with Schistosoma mansoni (BH strain, 100 cercariae/mouse) and were treated with an intraperitoneal dose after infection as follows: (1) Cramoll 1,4 (50 mg kg(-1) single dose - after 40 days of infection), (2) Cramoll 1,4 (7 mg kg(-1) daily dose - for 7 days after infection) and control (untreated mice). Mice were sacrificed 8 weeks after infection and adult worms were recovered from the portal-hepatic system. Livers were fixed in 10% (v/v) formaldehyde/0.15M NaCl and tissue sections were processed for haematoxilin and Masson's trichrome stainings. Mice infected subcutaneously harboured no or very few worms and hence the effect of Cramoll 1,4 could not be assessed. Results (P≤0.05) were obtained with Cramoll 1,4 using the two treatments, with reduction of: egg excretion (79 and 80%), adult worm recovery (71 and 79%) and liver granulomas (40 and 73.5%) in relation to control. This study showed the potential anti-helminthic activity of Cramoll 1,4 when tested against Schistosomiasis mansoni infection in mice.

Surface plasmon resonance study of protein-carbohydrate interactions using biotinylated sialosides

Lectins are carbohydrate binding proteins found in plants, animals, and microorganisms. They serve as important models for understanding protein-carbohydrate interactions at the molecular level. We report here the fabrication of a novel sensing interface of biotinylated sialosides to probe lectin-carbohydrate interactions using surface plasmon resonance spectroscopy (SPR). The attachment of carbohydrates to the surface using biotin-NeutrAvidin interactions and the implementation of an inert hydrophilic hexaethylene glycol spacer (HEG) between the biotin and the carbohydrate result in a well-defined interface, enabling desired orientational flexibility and enhanced access of binding partners. The specificity and sensitivity of lectin binding were characterized using Sambucus nigra agglutinin (SNA) and other lectins including Maackia amurensis lectin (MAL), concanavalin A (Con A), and wheat germ agglutinin (WGA). The results indicate that alpha2,6-linked sialosides exhibit high binding affinity to SNA, while alteration in sialyl linkage and terminal sialic acid structure compromises the affinity by a varied degree. Quantitative analysis yields an equilibrium dissociation constant (KD) of 777 +/- 93 nM for SNA binding to Neu5Ac alpha2,6-LHEB. Transient SPR kinetics confirms the K D value from the equilibrium binding studies. A linear relationship was obtained in the 10-100 microg/mL range with limit of detection of approximately 50 nM. Weak interactions with MAL, Con A, and WGA were also quantified. The control experiment with bovine serum albumin indicates that nonspecific interaction on this surface is insignificant over the concentration range studied. Multiple experiments can be performed on the same substrate using a glycine stripping buffer, which selectively regenerates the surface without damaging the sialoside or the biotin-NeutrAvidin interface. This surface design retains a high degree of native affinity for the carbohydrate motifs, allowing distinction of sialyl linkages and investigation pertaining to the effect of functional group on binding efficiency. It could be easily modified to identify and quantify binding patterns of any low-affinity biologically relevant systems, opening new avenues for probing carbohydrate-protein interactions in real time.

Response surface examination of the relationship between experimental conditions and product distribution in electrophoretically mediated microanalysis

This work presents the first known use of response surface methodology (RSM) in electrophoretically mediated microanalysis. This concept is demonstrated by examining the optimization of reaction conditions for the conversion of nicotinamide adenine dinucleotide to nicotinamide adenine dinucleotide, reduced form by glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) in the conversion of glucose-6-phosphate to 6-phosphogluconate. Experimental factors including voltage, enzyme concentration, and mixing time of reaction at the applied voltage were selected at three levels and tested in a Box-Behnken response surface design. Upon migration in a capillary under CE conditions, plugs of substrate and enzyme are injected separately in buffer and allowed to react at variable conditions. Extent of reaction and product ratios were subsequently determined by CE. The model predicted results are shown to be in good agreement (7.1% discrepancy difference) with experimental data. The use of chemometric RSM provides a direct relationship between electrophoretic conditions and product distribution of microscale reactions using CE, thereby offering a new and versatile approach to optimizing enzymatic experimental conditions.

Poly(ethylene oxide) facilitates the characterization of an affinity between strongly basic proteins with DNA by affinity capillary electrophoresis

In order to study kin17 protein-DNA affinity, we have developed a fast and reproducible capillary electrophoresis (CE) analysis of a strongly basic protein: kin17 protein, using a nonpermanent coating based on poly(ethylene oxide) (PEO) to avoid adsorption of kin17. The coating procedure was optimized to provide a residual and stable electroosmotic flow (EOF = 5 x 10(-5) cm(2)/V x s), exhibiting RSD of 0.3% and excellent long-term stability. Good intraday and interday reproducibility of kin17 migration times (0.8 and 0.3% relative standard deviation (RSD), respectively) enabled us to consider that the recovery percentage obtained for kin17 protein was satisfactory (79%). The potential of this PEO-based coating procedure was evaluated for affinity CE method in order to study the affinity of kin17 protein for two single-stranded DNA (ssDNA) models: polydeoxyadenylic acid and polydeoxycytidilic acid (pdA and pdC). Binding constants (1.5 x 10(7) +/- 17% and 1.7 x 10(7) + 25%M(-1)) were evaluated assuming a 1:1 affinity between kin17 and pdA or pdC, respectively.

Analysis of the interaction between hyaluronan and hyaluronan-binding proteins by capillary affinity electrophoresis: significance of hyaluronan molecular size on binding reaction

We developed a method for the analysis of the interaction between hyaluronan (HA) oligosaccharides and hyaluronan-binding proteins (HABPs) using capillary affinity electrophoresis (CAE). The method is based on high-resolution separation of fluorescent-labeled HA molecules in the presence of hyaluronan-binding proteins at different concentrations by capillary electrophoresis (CE) with laser-induced fluorescent detection. Hyaluronan-binding protein from bovine nasal cartilage interacts strongly with HA decasaccharide or larger oligosaccharides. Effect of the molecular size of HA oligomers clearly showed that longer carbohydrate chains than decasaccharide were required for recognition by HA binding protein. Interestingly, the interaction did not cause retardation of HA oligomers as observed in many binding reactions such as the interaction between pharmaceuticals and serum albumin, but showed disappearance of the oligomer peak. Although we cannot explain the accurate mechanism on the interaction, disappearance is probably due to low equilibrium rate between free and conjugate states. The present technique will be useful to compare the relative binding affinity, and to understand the mechanism on the interaction between hyaluronan and hyaluronan-binding proteins.

Estimation of binding constants for the substrate and activator of Rhodobacter sphaeroides adenosine 5'-diphosphate-glucose pyrophosphorylase using affinity capillary electrophoresis

Binding constants were determined for the activator fructose-6-phosphate (F6P) and substrate adenosine 5'-triphosphate (ATP) (in the presence and absence of F6P) to the recombinant wild-type (WT) Rhodobacter sphaeroides adenosine 5'-diphosphate-(ADP)-glucose pyrophosphorylase (ADPGlc PPase) using affinity capillary electrophoresis (ACE). In these binding studies, the capillary is initially injected with a plug of sample containing ADPGlc PPase and noninteracting standards. The sample is then subjected to increasing concentrations of F6P or ATP in the running buffer and electrophoresed. Analysis of the change in the migration times of ADPGlc PPase, relative to those of the noninteracting standards, as a function of the varying concentration of F6P or ATP yields a binding constant. The values obtained were in good agreement with kinetic parameters obtained from steady state activity assays. The method was extended to examine the F6P binding constants for the R33A and R22A enzymes and the ATP binding constants for the R8A enzyme in the presence and absence of F6P. The R33A enzyme has been shown by activity assays to be insensitive to F6P activation, indicating a defect in binding or in downstream transmission of the allosteric signal required for full activation. ACE indicated no apparent binding of F6P, supporting the former hypothesis. The R22A enzyme was shown by activity assays to have a approximately 15-fold decrease in apparent affinity for F6P compared to that of WT while ACE indicated an affinity comparable to that of WT; potential reasons for this discrepancy are discussed. The R8A enzyme as measured by activity assays exhibits reduced fold-activation by F6P compared to that of WT but increased apparent affinity for ATP in the presence of F6P. The ACE results were in good agreement with the activity assay data, confirming the increased affinity for ATP in the presence of F6P. This method demonstrates the quantitative ability of ACE to study different binding sites/ligand interactions in allosteric enzymes.

Molecular interaction in capillary electrophoresis

At the present time, affinity capillary electrophoresis is a well-established method for the measurement of binding constants involving 1:1 interactions. Many recent applications of this technique have illustrated its versatility. If affinity capillary electrophoresis is to be widely applied to the study of all types of interactions it is imperative that we consider that higher order interactions may be present. Applying proper equations or developing new models appropriate to the description of such systems is essential to obtaining reliable binding information.

Capillary affinity electrophoresis for the screening of post-translational modification of proteins with carbohydrates

Glycosylation is one of the most important post-translational events for proteins, affecting their functions in health and disease, and plays significant roles in various information traffics for intracellular and intercellular biological events (Hancock, W. S. J. Proteome Res. 2002, 1, 297). We have attempted to obtain the information on the numbers and amounts of carbohydrate chains. Interaction between carbohydrate chains and proteins that recognize them is a target to understand the biological roles of glycosylation. To date, there have been a few strategies for simultaneous analysis of the interactions between complex mixtures of carbohydrates and proteins. Here, we report an approach to categorize carbohydrate chains using a few glycoprotein samples as models for the studies on the analysis of post-translational modification of proteins with carbohydrates. A combination of some specific lectins was used as carbohydrate-binding proteins. The method is based on high-resolution separation of fluorescent-labeled carbohydrates by capillary electrophoresis with laser-induced fluorescent detection in the presence of carbohydrate-binding proteins at different concentrations. The present technique affords (1) simultaneous determination of carbohydrate chains, (2) binding specificity of the constituent carbohydrate chains to specific proteins, and (3) kinetic data such as the association constant of each carbohydrate. We found that the lectins employed in the present study could discriminate subtle difference in linkages and resolved the carbohydrate mixtures. The results will be useful, for example, to understand the biological events expressed with carbohydrate changes on the cell surface.

Analysis of biomolecular interactions using a miniaturized surface plasmon resonance sensor

A commercially available miniaturized surface plasmon resonance sensor has been investigated for its applicability to biological interaction analysis. The sensor was found to exhibit excellent repeatability and linearity for high-refractive index solutions and good reproducibility for the binding of proteins. Its detection limit for the monoclonal antibody M1 was found to be 2.1 fmol, which corresponds to a surface concentration of 21 pg/mm2. Simple surface immobilization procedures relying on biotin/avidin or glycoprotein/lectin chemistry have been explored. Equilibrium dissociation constants for the binding of the FLAG peptide to its monoclonal antibody (M1) and for the binding of concanavalin A to a glycoprotein have been determined. The close agreement of these measurements with values obtained by surface fluorescence microscopy and fluorescence correlation spectroscopy helps to validate the use of this device. Thus, this sensor shows promise as an inexpensive, portable, and accurate tool for bioanalytical applications in laboratory and clinical settings.

Capillary electrophoresis/electrospray ion trap mass spectrometry for the analysis of negatively charged derivatized and underivatized glycans

The increasing interest in the development of glycoproteins for therapeutic purposes has created a greater demand for methods to characterize the sugar moieties bound to them. Traditionally, released carbohydrates are derivatized using such methods as permethylation or fluorescent tagging prior to analysis by high performance liquid chromatography (HPLC), capillary electrophoresis (CE), or direct infusion mass spectrometry. However, little research has been performed using CE with on-line mass spectrometry (MS) detection. The CE separation of neutral oligosaccharides requires the covalent attachment of a charged species for electrophoretic migration. Among charged labels which have shown promise in assisting CE and HPLC separation is the fluorophore 8-aminonaphthalene-1,3,6-trisulfonic acid (ANTS). This report describes the qualitative profiling of charged ANTS-derivatized and underivatized complex glycans by CE with on-line electrospray ion trap mass spectrometry. Several neutral standard glycans including a maltooligosaccharide ladder were derivatized with ANTS and subjected to CE/UV and CE/MS using low pH buffers consisting of citric and 6-aminocaproic acid salts. The ANTS-derivatized species were detected as negative ions, and multiple stage MS analysis provided valuable structural information. Fragment ions were easily identified, showing promise for the identification of unknowns. N-Linked glycans released from bovine fetuin were used to demonstrate the applicability of ANTS derivatization followed by CE/MS for the analysis of negatively charged glycans. Analyses were performed on both underivatized and ANTS-derivatized species, and sialylated glycans were separated and detected in both forms. The ability of the ion trap mass spectrometer to perform multiple stage analysis was exploited, with MS5 information obtained on selected glycans. This technique presents a complementary method to existing methodologies for the profiling of glycan mixtures.

Review applications of capillary electrophoresis to the analysis of biotechnology-derived therapeutic proteins

The number of proteins produced by recombinant DNA technology continues to grow at a rapid pace. In this review, the emphasis is on proteins that are of therapeutic interest. Aspects of protein analysis, such as glycoform separation of proteins produced in mammalian cells and the separation of oligosaccharides for structure elucidation, are covered. The use of antibodies as therapeutic proteins is growing and currently antibodies are the largest class of proteins produced by biotechnology. This has merited a separate section on analysis of antibodies by capillary electrophoresis (CE). Applications of mass spectrometry as an ancillary technique, used in conjunction with CE, are also covered briefly. This review covers the literature since 1999.

The use of selective adsorbents in capillary electrophoresis-mass spectrometry for analyte preconcentration and microreactions: a powerful three-dimensional tool for multiple chemical and biological applications

Much attention has recently been directed to the development and application of online sample preconcentration and microreactions in capillary electrophoresis using selective adsorbents based on chemical or biological specificity. The basic principle involves two interacting chemical or biological systems with high selectivity and affinity for each other. These molecular interactions in nature usually involve noncovalent and reversible chemical processes. Properly bound to a solid support, an "affinity ligand" can selectively adsorb a "target analyte" found in a simple or complex mixture at a wide range of concentrations. As a result, the isolated analyte is enriched and highly purified. When this affinity technique, allowing noncovalent chemical interactions and biochemical reactions to occur, is coupled on-line to high-resolution capillary electrophoresis and mass spectrometry, a powerful tool of chemical and biological information is created. This paper describes the concept of biological recognition and affinity interaction on-line with high-resolution separation, the fabrication of an "analyte concentrator-microreactor", optimization conditions of adsorption and desorption, the coupling to mass spectrometry, and various applications of clinical and pharmaceutical interest.