Characterization of a polyclonal antihapten antibody by affinity capillary electrophoresis

Recent advances in affinity capillary electrophoresis for binding studies

The present review covers recent advances and important applications of affinity capillary electrophoresis (ACE). It provides an overview about various ACE types, including ACE-MS, the multiple injection mode, the use of microchips and field-amplified sample injection-ACE. The most common scenarios of the studied affinity interactions are protein-drug, protein-metal ion, protein-protein, protein-DNA, protein-carbohydrate, carbohydrate-drug, peptide-peptide, DNA-drug and antigen-antibody. Approaches for the improvements of ACE in term of precision, rinsing protocols and sensitivity are discussed. The combined use of computer simulation programs to support data evaluation is presented. In conclusion, the performance of ACE is compared with other techniques such as equilibrium dialysis, parallel artificial membrane permeability assay, high-performance affinity chromatography as well as surface plasmon resonance, ultraviolet, circular dichroism, nuclear magnetic resonance, Fourier transform infrared, fluorescence, MS and isothermal titration calorimetry.

Real-time observation of temperature-dependent protein–protein interactions using real-time dual-color detection system

This study examined the ability of a real-time dual-color detection system to allow direct observations of the kinetics of temperature-dependent protein-protein interaction at a single-molecule level. The primary target protein was an Alexa Fluor 488-labeled actin conjugate, which had been pre-incubated with an unlabeled rabbit anti-actin antibody (IgG). The complementary fluorescent protein was Alexa Fluor 633-labeled goat anti-rabbit IgG antibody, which interacts with the rabbit anti-actin antibody (IgG) bound to the Alexa Fluor 488-labeled actin conjugate. The individual protein molecules labeled with different fluorescent dyes in solution were effectively focused, interacted with the other protein molecules at 500 aM, and detected directly in real-time using the dual-wavelength (lambda(ex)=488 and 635 nm) laser-induced fluorescence detection system. The kinetics of the protein-protein interactions were examined at different temperatures (12-32 degrees C). At concentrations in the aM range, the number of bound complex molecules through the protein-protein interaction decreased gradually with time at a given temperature, and increased with decreasing temperature at a set time. A high concentration (above 500 pM) of the protein sample caused aggregation and nonspecific binding of the protein molecules, even though the protein molecules were not an example of complementary binding. The results demonstrated that the real-time kinetics of a protein-protein interaction could be analyzed effectively at the single-molecule level without any time delay using the real-time dual-color detection system.

Homopolyvalent antibody-antigen interaction kinetic studies with use of a dual-polarization interferometric biosensor

We used dual-polarization interferometry (DPI) to study the interaction kinetics between a 'homopolyvalent' antigen (Ag) and a monoclonal antibody (Ab). A model system, which uses a monoclonal Ab against a homopentameric Ag, C-reactive protein (CRP), is presented with principle and experiments for the study of the interactions between an Ab and an Ag that has multiple identical epitopes. This allows evaluation of the dissociation constant (K(D)) and of the binding stoichiometry by DPI based on measurements of phase changes of Ab-Ag complexes in the transverse magnetic (TM) and transverse electric (TE) polarization modes. The average experimental value of K(D) found by the DPI technique for anti-CRP Ab was shown to be in close agreement with the value obtained by an indirect competition-enzyme-linked immunosorbent assay (ELISA). Moreover, the total number of Ab combining sites on the DPI sensor chip was calculated, and the binding stoichiometry of the surface Ag-Ab complex was obtained. This study illustrates the advantages of the DPI method in biosensing in its capacity for simultaneous evaluation of the thickness and refractive index (density, mass) of adsorbed layers. This allowed a comprehensive analysis of affinity reactions between an Ab having two binding sites and a multi-sited Ag.

Importance of the counterion in optimization of a borate electrolyte system for analyses of anions in samples with complex matrices performed by capillary zone electrophoresis

Borate buffers are common background electrolytes for analyses of anions in capillary zone electrophoresis. Usually, sodium borate at a given pH is used and this specification seems to be sufficient for a successful analysis. In this paper, we show that free migration of OH(-) may deteriorate the analysis of a typical anionic analysis of clinical samples due to uncontrolled migration of OH(-) throughout the systems of analyzed zones and may damage the stacking of anionic analytes of interest. We have proven that the use of ammonium borate may remedy the situation where the presence of ammonium may selectively stop the free migration of OH(-) ions, slow down their effective mobility and bring their safe behavior resulting in reproducible stacking of clinically important anions. Results of real analyses of human serum samples confirmed the proposed method and proved that substitution of sodium for ammonium in borate buffers offers reliable analyses of clinical samples having chloride as the bulk component. The experimental results given in this paper are supported also by computer simulation, which can not only support the positive results but also show the dynamics of the separation that is otherwise hidden to any detection possibilities.

Immunoaffinity capillary electrophoresis: determination of binding constant and stoichiometry for antibody-antigen interaction

Affinity capillary electrophoresis (ACE) can provide both qualitative and quantitative information on molecular interactions and affords the advantages of very low sample consumption, high mass sensitivity, short analysis time, and the use of automated instrumentation. It has been applied clinically and biochemically to the determination of the binding constant and to the measurement of the binding stoichiometry for interactions between antibodies (Ab's) and antigens (Ag's) in free solution. In many situations, the Ag molecule has two or multiple binding sites, each of which has a similar or different intrinsic affinity for binding independently to the combining site(s) on an Ab molecule. The multivalent binding reactions between Ab and Ag molecules often occur. The objective of this review is to describe the uses of ACE in the determination of binding constants and stoichiometry of Ab-Ag interactions (immunoaffnity capillary electrophoresis), focusing especially on multivalent Ab-Ag interaction modes. Five model binding systems developed recently using ACE techniques are described with principles and examples: (i) divalent mAb-monovalent Ag interaction, (ii) divalent mAb-(homo)polyvalent Ag interaction, (iii) cooperativity of two binding sites of mAb-monovalent Ag interaction, (iv) monovalent Fab-divalent Ag interaction, and (v) polyclonal Ab-monovalent Ag interaction. Finally, the determination of binding stoichiometry of Ab-Ag interactions by ACE is described.