Affinophoresis: selective electrophoretic separation of proteins using specific carriers

Lectin affinity electrophoresis

An interaction or a binding event typically changes the electrophoretic properties of a molecule. Affinity electrophoresis methods detect changes in the electrophoretic pattern of molecules (mainly macromolecules) that occur as a result of biospecific interactions or complex formation. Lectin affinity electrophoresis is a very effective method for the detection and analysis of trace amounts of glycobiological substances. It is particularly useful for isolating and separating the glycoisomers of target molecules. Here, we describe a sensitive technique for the detection of glycoproteins separated by agarose gel-lectin affinity electrophoresis that uses antibody-affinity blotting. The technique is tested using α-fetoprotein with lectin (Lens culinaris agglutinin and Phaseolus vulgaris agglutinin)-agarose gels.

Determination of the affinity constants of recombinant human galectin-1 and -3 for simple saccharides by capillary affinophoresis

The affinity constants of recombinant human galectin-1 and galectin-3 for sugars were determined by capillary affinophoresis. The monoliganded affinophore contains p-aminophenyl-beta-lactoside as an affinity ligand in the matrix of succinylglutathione and has three negative charges. An analysis of the mobility change of the lectins caused by the affinophore and its inhibition by neutral sugars allowed, for the first time, a determination of the affinity constants between the binding sites of the lectins and sugars. The relative magnitude of the affinity constants for each of the sugars in terms of dissociation constants found to be consistent with previously reported data on the concentrations of sugars that caused a 50% inhibition (I50) in the binding assay of the lectin to oligosaccharide-immobilized agarose beads but the absolute values of the dissociation constants were considerably smaller than the I50 values. Capillary affinophoresis indicated microheterogeneity of the lectin preparations and enabled the separate analysis of the affinity of each component simultaneously showing the advantage in using a separation method for analysis of bioaffinity.

Prevention of evaporation of small-volume sample solutions for capillary electrophoresis using a mineral-oil overlay

The suppression of evaporation of water from small volumes of sample solutions or reagents for capillary electrophoresis by the use of a mineral-oil overlay was investigated in affinophoresis applications, in which the affinity constant of a mutant protein of recombinant human galectin-1 to a lactose affinophore, a triply negative charged ion having a lactoside as an affinity ligand, was determined. When an injection was carried out from a minimum of 20 microL of an aqueous solution beneath the oil overlay, no oil contamination inside the capillary was observed, provided the capillary was cleanly cut so that the end was flat, and the polyimide coating had been removed for a distance of about 2 mm from the end. Affinophoresis was carried out using 20 microL of an affinophore solution covered with an oil overlay. The abnormalities in the electropherograms as the result of the evaporation of the water from the solution during storage prior to use in an automatic operation of a capillary electrophoresis instrument were suppressed, with respect to the formation of a base line gap, an increase in the detection time of a marker ion and an increase in the initial current. A solution in a vial could be used repeatedly for a longer period of time when overlaid with mineral oil than in the absence of an overlay. The use of a mineral-oil overlay is a simple but very efficient technique for solving the problem of the evaporation of water from small volumes of aqueous solutions for use in capillary electrophoresis.

Ultratrace analysis of drugs in biological fluids using affinity probe capillary electrophoresis: analysis of dorzolamide with fluorescently labeled carbonic anhydrase

This work demonstrates the use of affinity probe capillary electrophoresis (APCE) in the quantitative analysis of drugs in biological fluids at the low pM level. The interaction of human carbonic anhydrase II (HCAII) with the glaucoma drug dorzolamide (Dz) was chosen as a model system. HCAII was labeled at its single cysteine residue using a thiol-specific fluorescein reagent. The peak area of HCAII complexed with the tight-binding drug Dz provided a direct assay of the drug concentration in solution. A charged competitive ligand added to the running buffer was employed in APCE to distinguish Dz-bound from free forms of the HCAII. Using laser-induced fluorescence (LIF), the Dz detection limit was 16.5 pM in aqueous solution and 62.5 pM in both urine and plasma. Normalized peak area reproducibility of the drug was within 3.4% RSD. Each analysis was completed within 10 min, including incubation, and consumed only 0.3 pmol of labeled protein. The APCE approach provides an effective method for trace level detection of drugs in biological matrices.

Identification, quantitation, and characterization of biomolecules by capillary electrophoretic analysis of binding interactions

The high resolving power of capillary electrophoresis combined with the specificity of binding interactions may be used with advantage to characterize the structure-function relationship of biomolecules, to quantitate specific analytes in complex sample matrices, and to determine the purity of pharmaceutical and other molecules. We here review recent and innovative methodologies and applications of high resolution affinity electrophoresis within the fields of binding constant determination, structure-activity studies, quantitative microassays, analysis of drug purity and protein conformation, and immobilized affinity ligands. Despite the virtues of these approaches with respect to applicability, resolving power, speed, and low sample consumption, problems remain with respect to analyte identification and low concentration limits of detection. The ongoing development of new detector technologies for capillary electrophoresis such as mass spectrometry, and possibly nuclear magnetic resonance and other spectroscopic methods, is therefore very promising for the continued increased use of affinity capillary electrophoresis.

Electrophoretic methods for studying protein-protein interactions

Protein-protein interactions are involved in many biological processes ranging from DNA replication, to signal transduction, to metabolism control, to viral assembly. The understanding of those interactions would allow the effective design of new drugs and further manipulation of those interactions. Several useful analytical methods are available for the study of protein-protein binding, and among them, electrophoresis is commonly used. We describe two types of electrophoresis: gel electrophoresis and capillary electrophoresis. Gel electrophoresis is a well-established method used to study protein-protein interactions and includes overlay gel electrophoresis, charge shift method, band shift assay, countermigration electrophoresis, affinophoresis, affinity electrophoresis, rocket immunoelectrophoresis, and crossed immunoelectrophoresis. These techniques are briefly described along with their advantages and limitations. Capillary electrophoresis, on the other hand, is a relatively new method and affinity capillary electrophoresis has demonstrated its value in the measurement of binding constants, the estimation of kinetic rate constants, and the determination of stoichiometry of biomolecular interactions. It offers short analysis time, requires minute amounts of protein samples, usually involves no radiolabeled compounds, and, most importantly, is carried out in solution. We summarize the principles of affinity capillary electrophoresis for studying protein-protein interactions along with current limitations and describe in depth its application to the determination of stoichiometries of tight and weak binding protein-protein interactions. The protocol presented in the experimental section details the use of affinity capillary electrophoresis for the determination of stoichiometry of protein complexes.

Capillary affinophoresis of pea lectin with polyliganded affinophores: a model study of divalent-polyvalent interactions

Affinophoresis is a type of affinity electrophoresis using an affinophore, a soluble ionic carrier bearing affinity ligand(s). It was reported previously that an affinophore, prepared by coupling multiple p-aminophenyl alpha-D-mannoside ligands to a part of the carboxyl groups of succinylated polylysine, specifically changed the mobility of pea lectin in agarose gel. The affinophoresis of this divalent lectin with the polyliganded affinophore was investigated by using capillary electrophoresis. Analysis of the mobility change of the lectin in the presence of differently modified affinophores showed that the affinity was larger for affinophores having higher ligand density. Analysis of the inhibition of the mobility change by a neutral ligand, with a known affinity constant for the lectin, allowed estimation of the contributions of monovalent and divalent interactions to the binding in the lectin-affinophore complex. The proportion of divalent complexes was greater for affinophores having higher ligand density. This approach to estimate the contribution of divalency in complex formation should be generally applicable to the analysis of divalent interactions with different techniques other than electrophoresis.

Capillary affinophoresis as a versatile tool for the study of biomolecular interactions: a mini-review

Combination of capillary electrophoresis and bioaffinity interaction gave rise to powerful research tools for analyzing molecular recognition. They take advantages of the electrophoretic behavior of the complex formed between a target biomolecule and a specially designed mobile ligand molecule (affinophore or affinity probe), and enable detection of complex formation, determination of the equilibrium constants and stoichiometry, etc.