Recent advances in affinity capillary electrophoresis

Capillary electrophoresis-mass spectrometry for protein analyses under native conditions: Current progress and perspectives

Native mass spectrometry is a rapidly emerging technique for fast and sensitive structural analysis of protein constructs, maintaining the protein higher order structure. The coupling with electromigration separation techniques under native conditions enables the characterization of proteoforms and highly complex protein mixtures. In this review, we present an overview of current native CE-MS technology. First, the status of native separation conditions is described for capillary zone electrophoresis (CZE), affinity capillary electrophoresis (ACE), and capillary isoelectric focusing (CIEF), as well as their chip-based formats, including essential parameters such as electrolyte composition and capillary coatings. Further, conditions required for native ESI-MS of (large) protein constructs, including instrumental parameters of QTOF and Orbitrap systems, as well as requirements for native CE-MS interfacing are presented. On this basis, methods and applications of the different modes of native CE-MS are summarized and discussed in the context of biological, medical, and biopharmaceutical questions. Finally, key achievements are highlighted and concluded, while remaining challenges are pointed out.

Analysis of drug interactions with serum proteins and related binding agents by affinity capillary electrophoresis: A review

Biomolecules such as serum proteins can interact with drugs in the body and influence their pharmaceutical effects. Specific and precise methods that analyze these interactions are critical for drug development or monitoring and for diagnostic purposes. Affinity capillary electrophoresis (ACE) is one technique that can be used to examine the binding between drugs and serum proteins, or other agents found in serum or blood. This article will review the basic principles of ACE, along with related affinity-based capillary electrophoresis (CE) methods, and examine recent developments that have occurred in this field as related to the characterization of drug-protein interactions. An overview will be given of the various formats that can be used in ACE and CE for such work, including the relative advantages or weaknesses of each approach. Various applications of ACE and affinity-based CE methods for the analysis of drug interactions with serum proteins and other binding agents will also be presented. Applications of ACE and related techniques that will be discussed include drug interaction studies with serum agents, chiral drug separations employing serum proteins, and the use of CE in hybrid methods to characterize drug binding with serum proteins.

Advances in Studying Glycosaminoglycan-Protein Interactions Using Capillary Electrophoresis

Methods for studying interactions between glycosaminoglycans (GAGs) and proteins have assumed considerable significance as their biological importance increases. Capillary electrophoresis (CE) is a powerful method to study these interactions due to its speed, high efficiency, and low sample/reagent consumption. In addition, CE works effectively under a wide range of physiologically relevant conditions. This chapter presents the state of the art on CE methods for studying GAG-protein interactions including affinity capillary electrophoresis (ACE), capillary zone electrophoresis (CZE), frontal analysis (FA)/frontal analysis continuous capillary electrophoresis (FACCE), and capillary electrokinetic chromatography (CEC) with detailed experimental protocols for ACE and CZE methods.

Non-Receptor-Mediated Lipid Membrane Permeabilization by the SARS-CoV-2 Spike Protein S1 Subunit

Due to the pressing need to generate specific drugs or vaccines for COVID-19 and management of its outbreak, detailed knowledge regarding the SARS-CoV-2 entry into host cells and timely, cheap, and easy-to-use detection methods are of critical importance for containing the SARS-CoV-2 epidemic. Through electrophysiology and fluorescence spectroscopy experiments, we show that even in the absence of the angiotensin-converting enzyme 2 receptor, the S1 subunit from SARS-CoV-2 spike protein binding to neutral phospholipid membranes leads to their mechanical destabilization and permeabilization. A similar cytotoxic effect of the protein was seen in human lung epithelial cells. A monoclonal antibody generated toward the S1 subunit alleviates to a considerable extent the destabilizing potential of the protein in such model membranes. Finally, we demonstrate the proof-of-concept capability of an α-hemolysin (α-HL) protein nanopore to detect in aqueous buffer and real time the region-binding domain of the S1 subunit from SARS-CoV-2 spike protein by monitoring its immunological interaction with a target antibody. Our results may offer new perspectives in understanding the pathogenesis of the SARS-CoV-2 infection, its treatment, and real-time detection.

Recent Advances and Applications of Microfluidic Capillary Electrophoresis: A Comprehensive Review (2017-Mid 2019)

Microfluidic capillary electrophoresis (MCE) is the novel technique resulted from the CE mininaturization as planar separation and analysis device. This review presents and discusses various application fields of this advanced technology published in the period 2017 till mid-2019 in eight different sections including clinical, biological, single cell analysis, environmental, pharmaceuticals, food analysis, forensic and ion analysis. The need for miniaturization of CE and the consequence advantages achieved are also discussed including high-throughput, miniaturized detection, effective separation, portability and the need for micro- or even nano-volume of samples. Comprehensive tables for the MCE applications in the different studied fields are provided. Also, figure comparing the number of the published papers applying MCE in the eight discussed fields within the studied period is included. The future investigation should put into consideration the possibility of replacing conventional CE with the MCE after proper validation. Suitable validation parameters with their suitable accepted ranges should be tailored for analysis methods utilizing such unique technique (MCE).

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.

Moment analysis for reaction kinetics of intermolecular interactions

Moment equations were developed on the basis of the principle of relativity for analyzing elution peak profiles measured by ACE to analytically determine the association (k_a ) and dissociation (k_d ) rate constants of intermolecular interactions. Basic equations representing the mass balance, mass transfer rate, and reaction kinetics in ACE system in a Galilean coordinate system S were transformed to those in another coordinate system S', which imaginarily moved with respect to S. Moment equations for ACE peaks in S' in the time domain were derived from the analytical solution of the modified basic equations in the Laplace domain. Moment equations for ACE peaks in S were derived from those in S' by the inverse Galilean transformation. The moment equations were used for analyzing some ACE data previously published to determine k_a and k_d values. It was demonstrated that the moment equations were effective for extracting the information about affinity kinetics of intermolecular interactions from the elution peak profiles measured by ACE. The moment equations were also used to discuss the influence of mass transfer and reaction kinetics on ACE peak profiles. Some results of the numerical calculations are also indicated in Supporting Information.

Current landscape of protein glycosylation analysis and recent progress toward a novel paradigm of glycoscience research

This review covers the basics and some applications of methodologies for the analysis of glycoprotein glycans. Analytical techniques used for glycoprotein glycans, including liquid chromatography (LC), capillary electrophoresis (CE), mass spectrometry (MS), and high-throughput analytical methods based on microfluidics, were described to supply the essentials about biopharmaceutical and biomarker glycoproteins. We will also describe the MS analysis of glycoproteins and glycopeptides as well as the chemical and enzymatic releasing methods of glycans from glycoproteins and the chemical reactions used for the derivatization of glycans. We hope the techniques have accommodated most of the requests from glycoproteomics researchers.

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.

Studying glycosaminoglycan-protein interactions using capillary electrophoresis

Methods for studying interactions between glycosaminoglycans (GAGs) and proteins have assumed considerable significance as their biological importance increases. Capillary electrophoresis (CE) is a powerful method to study these interactions due to its speed, high efficiency, and low sample/reagent consumption. In addition, CE works effectively under a wide range of physiologically relevant conditions. This chapter presents state-of-the-art on CE methods for studying GAG-protein interactions including affinity capillary electrophoresis (ACE), capillary zone electrophoresis (CZE), frontal analysis (FA)/frontal analysis continuous capillary electrophoresis (FACCE), and capillary electrokinetic chromatography (CEC) with detailed experimental protocols for ACE and CZE methods.

Lab-on-a-chip: emerging analytical platforms for immune-mediated diseases

Miniaturization of analytical procedures has a significant impact on diagnostic testing since it provides several advantages such as: reduced sample and reagent consumption, shorter analysis time and less sample handling. Lab-on-a-chip (LoC), usually silicon, glass, or silicon-glass, or polymer disposable cartridges, which are produced using techniques inherited from the microelectronics industry, could perform and integrate the operations needed to carry out biochemical analysis through the mechanical realization of a dedicated instrument. Analytical devices based on miniaturized platforms like LoC may provide an important contribution to the diagnosis of high prevalence and rare diseases. In this paper we review some of the uses of Lab-on-a-chip in the clinical diagnostics of immune-mediated diseases and we provide an overview of how specific applications of these technologies could improve and simplify several complex diagnostic procedures.

Probing tRNA interaction with biogenic polyamines

Biogenic polyamines are found to modulate protein synthesis at different levels. This effect may be explained by the ability of polyamines to bind and influence the secondary structure of tRNA, mRNA, and rRNA. We report the interaction between tRNA and the three biogenic polyamines putrescine, spermidine, spermine, and cobalt(III)hexamine at physiological conditions, using FTIR spectroscopy, capillary electrophoresis, and molecular modeling. The results indicated that tRNA was stabilized at low biogenic polyamine concentration, as a consequence of polyamine interaction with the backbone phosphate group. The main tRNA reactive sites for biogenic polyamine at low concentration were guanine-N7/O6, uracil-O2/O4, adenine-N3, and 2'OH of the ribose. At high polyamine concentration, the interaction involves guanine-N7/O6, adenine-N7, uracil-O2 reactive sites, and the backbone phosphate group. The participation of the polycation primary amino group, in the interaction and the presence of the hydrophobic contact, are also shown. The binding affinity of biogenic polyamine to tRNA molecule was in the order of spermine > spermidine > putrescine with K(Spm) = 8.7 × 10(5) M(-1), K(Spd) = 6.1 × 10(5) M(-1), and K(Put) = 1.0 × 10(5) M(-1), which correlates with their positively charged amino group content. Hill analysis showed positive cooperativity for the biogenic polyamines and negative cooperativity for cobalt-hexamine. Cobalt(III)hexamine contains high- and low-affinity sites in tRNA with K(1) = 3.2 × 10(5) M(-1) and K(2) = 1.7 × 10(5) M(-1), that have been attributed to the interactions with guanine-N7 sites and the backbone PO(2) group, respectively. This mechanism of tRNA binding could explain the condensation phenomenon observed at high Co(III) content, as previously shown in the Co(III)-DNA complexes.

Quantification of single-stranded nucleic acid and oligonucleotide interactions with metal ions by affinity capillary electrophoresis--Part II

The interactions between tetranucleotides or heptanucleotides and inorganic cations have been measured by affinity CZE. The variation in migration behavior with increasing concentrations of divalent cations (Ca(2+), Mg(2+) and Ni(2+)) in the running buffer was investigated and quantified by the calculation of binding constants for mononuclear and multinuclear interactions. In addition to these fundamental studies of binding equilibria, the effect of sequence and the position of the guanine transition metal-binding site in the oligonucleotide have been investigated.

Determination of binding constants by affinity capillary electrophoresis, electrospray ionization mass spectrometry and phase-distribution methods

Many methods for determining intermolecular interactions have been described in the literature in the past several decades. Chief among them are methods based on spectroscopic changes, particularly those based on absorption or nuclear magnetic resonance (NMR) [especially proton NMR ((1)H NMR)]. Recently, there have been put forward several new methods that are particularly adaptable, use very small quantities of material, and do not place severe requirements on the spectroscopic properties of the binding partners. This review covers new developments in affinity capillary electrophoresis, electrospray ionization mass spectrometry (ESI-MS) and phasetransfer methods.

Strategies for label-free optical detection

A large number of methods using direct detection with label-free systems are known. They compete with the well-introduced fluorescence-based methods. However, recent applications take advantage of label-free detection in protein-protein interactions, high-throughput screening, and high-content screening. These new applications require new strategies for biosensors. It becomes more and more obvious that neither the transduction principle nor the recognition elements for the biomolecular interaction process alone determine the quality of the biosensor. Accordingly, the biosensor system has to be considered as a whole. This chapter focuses on strategies to optimize the detection platform and the biomolecular recognition layer. It concentrates on direct detection methods, with special focus on optical transduction. Since even this restriction still leaves a large number of methods, only microrefractometric and microreflectometric methods using planar transducers have been selected for a detailed description and a listing of applications. However, since many review articles on the physical principles exist, the description is kept short. Other methods are just mentioned in brief and for comparison. The outlook and the applications demonstrate the future perspectives of direct optical detection in bioanalytics.

Moment analysis of near-equilibrium binding interactions during electrophoresis

The electrophoretic transport of three chemically reacting species, two of which can bind reversibly to form the third, is analyzed mathematically. The species are assumed to move horizontally through a long channel with different electrophoretic mobilities and diffusion coefficients. By considering small perturbations of the system about equilibrium or when one of the two binding species is much more abundant than the other, the governing advection-reaction-diffusion equations can be linearized and studied via the method of moments. The result is a set of coupled ordinary differential equations for the moments that can be solved analytically. Analysis of the long-time evolution of the moments yields mean velocities and dispersion coefficients for each species. The results provide a method for measuring the rate and equilibrium constants of binding reactions using capillary electrophoresis.

CE frontal analysis employing contactless conductivity detection for determination of CMCs of non-UV absorbing charged surfactants

Micellar systems composed of surfactants are used extensively in academia and industry for many different applications. In this work a highly versatile CE method for determination of CMCs of charged surfactants has been developed. In the case of positively charged surfactants a coating procedure of the fused-silica capillary was used, whereas negatively charged surfactants were analyzed using uncoated capillaries. The CE method is based on frontal analysis (FA) employing use of contactless conductivity and UV detection. The main advantages of the method are that it can be used for non-UV absorbing surfactants without introducing marker compounds which previously has been found to affect CMCs, requires very limited sample volume and is easily implemented and automated using standard CE equipment. The fact that counterions and different aggregated states are separated allows a detailed characterization of the micelle systems using the developed method. In the case of UV absorbing surfactants similar results were obtained employing contactless conductivity and UV detection. Finally, CMCs obtained using conductometry gave similar results as compared to the developed CE-FA procedure.

Potential of label-free detection in high-content-screening applications

The classical approach of high-content screening (HCS) is based on multiplexed, functional cell-based screening and combines several analytical technologies that have been used before separately to achieve a better level of automation (scale-up) and higher throughput. New HCS methods will help to overcome the bottlenecks, e.g. in the present development chain for lead structures for the pharmaceutical industry or during the identification and validation process of new biomarkers. In addition, there is a strong need in analytical and bioanalytical chemistry for functional high-content assays which can be provided by different hyphenated techniques. This review discusses the potential of a label-free optical biosensor based on reflectometric interference spectroscopy (RIfS) as a bridging technology for different HCS approaches. Technical requirements of RIfS are critically assessed by means of selected applications and compared to the performance characteristics of surface plasmon resonance (SPR) which is currently the leading technology in the area of label-free optical biosensors.

Why are proteins charged? Networks of charge-charge interactions in proteins measured by charge ladders and capillary electrophoresis

Almost all proteins contain charged amino acids. While the function in catalysis or binding of individual charges in the active site can often be identified, it is less clear how to assign function to charges beyond this region. Are they necessary for solubility? For reasons other than solubility? Can manipulating these charges change the properties of proteins? A combination of capillary electrophoresis (CE) and protein charge ladders makes it possible to study the roles of charged residues on the surface of proteins outside the active site. This method involves chemical modification of those residues to generate a large number of derivatives of the protein that differ in charge. CE separates those derivatives into groups with the same number of modified charged groups. By studying the influence of charge on the properties of proteins using charge ladders, it is possible to estimate the net charge and hydrodynamic radius and to infer the role of charged residues in ligand binding and protein folding.

Spectral differentiation and immunoaffinity capillary electrophoresis separation of enantiomeric benzo(a)pyrene diol epoxide-derived DNA adducts

Antibody cross-reactivity makes separation and differentiation of enantiomeric analytes one of the most challenging problems in immunoanalytical research, particularly for the analysis of structurally related biological molecules [such as benzo( a)pyrene (BP) metabolites and BP-derived DNA adducts]. It has recently been shown that the interaction of enantiomers of BP tetrols (BPT) with a promiscuous anti-polycyclic aromatic hydrocarbon ( anti-PAH) monoclonal antibody (mAb) allowed for separation of all four enantiomeric isomers using immunoaffinity capillary electrophoresis [ Grubor, N. M. , Armstrong, D. W. , and Jankowiak, R. ( 2006) Electrophoresis 27, 1078 ] and unambiguous spectral resolution using fluorescence line narrowing spectroscopy (FLNS) [ Grubor, N. M. , Liu, Y. , Han, X. , Armstrong, D.W. , and Jankowiak, R. ( 2006) J. Am.Chem. Soc. 128, 6409 ]. Here, we expand the use of the above two methodologies to the group of biologically important molecules that are products of BP diol epoxide (BPDE)-induced DNA damage. Four diastereomeric anti-BPDE-derived deoxyguanosine (dG) adducts, that is, (+)- and (-)- anti-trans-BPDE- N (2)-dG and (+)- and (-)- anti-cis-BPDE- N (2)-dG, were electrophoretically separated and spectroscopically differentiated using 8E11 mAb raised against BP-DNA conjugates. In fluorescence line narrowing spectroscopy (FLNS) experiments, complexes of BPDE-dG adducts with mAb revealed differences in fluorescence origin band positions, bandwidths, and vibrational patterns for all four BPDE- N (2)-dG adducts. Narrow fluorescence origin bands observed for (-)- trans-BPDE-dG (70 cm (-1)) and (+)- trans-BPDE- N (2)-dG (80 cm (-1)) suggest spatial constraint within the mAb binding pocket. Broader origin bands observed for cis type adducts ( approximately 120 cm (-1)) in 8E11 mAb suggest different binding geometries and/or conformational changes, as also indicated by changes in vibrational frequencies observed for the (+)- anti-cis and (-)- anti-cis adducts complexed with mAb. FLNS revealed that binding conformations and interactions within the mAb binding pocket are different for each adduct, enabling unambiguous positive identification. The methodologies described in this manuscript could also be used for analysis of DNA adducts following enzymatic hydrolysis of BPDE-adducted DNA to free nucleosides.

Determination of binding constants of vasoactive intestinal peptide to poly(amidoamine) dendrimers designed for drug delivery using ACE

The purpose of the present paper was to study at physiological pH the affinity between vasoactive intestinal peptide (VIP) and four poly(amidoamine) dendrimers (PAMAMs) designed for drug delivery. Therefore, a fast and reproducible CE method was first developed to analyze the strongly basic peptide. To allow an accurate determination of binding constant (K) values, the ability to suppress peptide adsorption onto the silica capillary of nonpermanent coatings (poly(ethylene oxide) (PEO), low and medium relative molecular masses poly(diallyldimethylammonium chloride) (PDDA)) or poly(acrylamide) permanent coating (PAA) was evaluated. Very good intraday repeatability of VIP migration times and peak areas (0.1-0.6 and 2.9-4.9% RSD, respectively) was obtained using two of the investigated coatings (PEO and PDDA with medium molecular mass). ACE combined with these dynamic coatings was then employed to evaluate K between VIP and two amine-terminated PAMAM dendrimers of generation 2 and 5 (G2.NH2, G5.NH2) and two carboxyl-terminated PAMAM derivatives of generation 2 and 5 (G2.COOH, G5.COOH). Binding constant of (6.7 +/- 1.1) x 10(4)/M could be determined for the couple VIP/G5.NH2, while no affinity was evidenced between VIP and all other dendrimers investigated. These results suggest that G5.NH2 might be an interesting carrier for the delivery of VIP.

Stability constants of amino acids, peptides, proteins, and other biomolecules determined by CE and related methods: Recapitulation of published data

The stability (affinity, association, binding, complexation, formation) constant characterizes binding interaction between the analyte and the complexing agent. Knowledge of the stability constant makes possible the prediction and estimation of the binding behavior of constituents (amino acids, peptides, proteins, drugs, antibiotics, enzymes, enantiomers) to their partners, and the finding of a suitable partner for the given analyte to form a stable complex. The present paper summarizes the stability constant determination methods and the approaches used to evaluate the experimental data. Further, the paper recapitulates the published stability constant values determined, mainly, by capillary electrophoretic methods, taken from the Web of Science database covering the last decade. Details of the experimental conditions employed for the determination of the stability constants are also given. The review attempts to give a critical evaluation of the problems that accompany the determination of stability constant and discusses their solution.

CE frontal analysis based on simultaneous UV and contactless conductivity detection: A general setup for studying noncovalent interactions

CE frontal analysis (CE-FA) has been established as a powerful tool to study noncovalent interactions between macromolecules and small molecules such as drug substances or pharmaceutical excipients. However, when using traditional commercial CE instrumentation, a serious drawback is related to the fact that only UV-active compounds can be studied. In recent years, contactless conductivity detection has become an attractive alternative to UV detection in CE due to its high versatility. In this study, we combine contactless conductivity detection and UV detection in a highly versatile setup for profiling noncovalent interactions between low-molecular-weight molecules and macromolecules. In the case of molecules having a chromophore the setup allows determination of binding constants using two independent detectors. The new contactless conductivity detection cell is compatible with commercial CE instrumentation and is therefore easily implemented in any analysis laboratory with CE expertise.

Bioanalytical interaction studies executed by preincubation affinity capillary electrophoresis

The versatility of CE is beneficial for the study of many types of molecular interactions, because different experimental designs can be made to suit the characteristics of a particular interaction. A very versatile starting point is the preequilibration type of affinity CE that has been used extensively for characterizing biomolecular interactions in the last 15 years. We review this field here and include a comprehensive overview of the existing preincubation ACE modes including their advantages and limitations as well as the methodological developments and applications within the bioanalytical field.

Biomolecular interaction analysis under electrophoretic flow conditions

Combining the advantages of electrophoresis with the advantages of biomolecular interaction analysis (BIA) enables the biospecific detection of separated molecules; for example it permits differentiation between a complementary single-stranded DNA and a single nucleotide polymorphism. In order to integrate these two techniques, it is necessary to investigate whether it is possible to detect a biomolecular interaction under electrophoretic flow conditions. To this end a novel detection system was developed for electrophoresis that utilizes a label-free and time-resolved detection technique: reflectometric interference spectroscopy (RIfS). The biological functions of important analytes were investigated using this system. Although RIfS can be used as a postcolumn detector, it is also possible to use it to detect relevant substances under electrophoretic flow conditions. DNA-LNA, biotin-streptavidin and protein-protein interactions were detected using this coupled electrophoresis-RIfS set-up.

Polymeric microfluidic system for DNA analysis

The application of micro total analysis system (microTAS) has grown exponentially in the past decade. DNA analysis is one of the primary applications of microTAS technology. This review mainly focuses on the recent development of the polymeric microfluidic devices for DNA analysis. After a brief introduction of material characteristics of polymers, the various microfabrication methods are presented. The most recent developments and trends in the area of DNA analysis are then explored. We focus on the rapidly developing fields of cell sorting, cell lysis, DNA extraction and purification, polymerase chain reaction (PCR), DNA separation and detection. Lastly, commercially available polymer-based microdevices are included.

Measurement of monomolecular binding constants of neutral phenols into the beta-cyclodextrin by continuous frontal analysis in capillary and microchip electrophoresis via a competitive assay

Measurement of binding constant by chip electrophoresis is a very promising technique for the high throughput screening of non-covalent interactions. Among the different electrophoretic methods available that yield the binding parameters, continuous frontal analysis is the most appropriate for a transposition from capillary electrophoresis (CE) to microchip electrophoresis. Implementation of this methodology in microchip was exemplified by the measurement of inclusion constants of 2-naphtalenesulfonate and neutral phenols (phenol, 4-chlorophenol and 4-nitrophenol) into beta-cyclodextrin by competitive assays. The issue of competitor choice is discussed in relation to its appropriateness for proper monitoring of the interaction.

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.

Micro-separation toward systems biology

Current biology is experiencing transformation in logic or philosophy that forces us to reevaluate the concept of cell, tissue or entire organism as a collection of individual components. Systems biology that aims at understanding biological system at the systems level is an emerging research area, which involves interdisciplinary collaborations of life sciences, computational and mathematical sciences, systems engineering, and analytical technology, etc. For analytical chemistry, developing innovative methods to meet the requirement of systems biology represents new challenges as also opportunities and responsibility. In this review, systems biology-oriented micro-separation technologies are introduced for comprehensive profiling of genome, proteome and metabolome, characterization of biomolecules interaction and single cell analysis such as capillary electrophoresis, ultra-thin layer gel electrophoresis, micro-column liquid chromatography, and their multidimensional combinations, parallel integrations, microfabricated formats, and nano technology involvement. Future challenges and directions are also suggested.

Characterization of polyanion-protein complexes by frontal analysis continuous capillary electrophoresis and small angle neutron scattering: effect of polyanion flexibility

The binding constant (K(obs)) for the beta-lactoglobulin-poly(vinylsulfate) (BLG-PVS) complex was measured by frontal analysis continuous capillary electrophoresis at pH values above the isoelectric point of BLG, and the persistence length (L(p)) of PVS was measured by small angle neutron scattering, to examine the effect of polyelectrolyte chain stiffness on its binding efficiency to proteins. The values of K(obs) and L(p) were compared with those of BLG-PSS and BLG-PAMPS (poly(2-acrylamido-2-methylpropanesulfonate)) reported previously. The relationship between K(obs) and L(p) was reciprocal, indicating that protein binding is enhanced by the flexibility of the polyanion, at least in the case where the net protein charge is negative. In addition, at a fixed pH, the polymer systems displayed a similar ionic strength dependence of K(obs). This similarity was consistent with the proposal that the binding properties of PVS and PAMPS polyanions are governed purely by electrostatic interactions and are independent of their molecular structure.

Peak shape modeling by Haarhoff-Van der Linde function for the determination of correct migration times: A new insight into affinity capillary electrophoresis

Among the different experimental strategies available in capillary electrophoresis (CE) to determine binding parameters, affinity capillary electrophoresis (ACE) has been the most widely embraced due to its easiness of implementation and of data handling. Ligand-substrate binding constants are thus directly derived from the substrate migration time shifts resulting from the variation of ligand concentration introduced in a background electrolyte. Classically, the substrate migration time is measured on top of the electrophoretic peak, assuming symmetrical peak shape. Depending on both substrate and ligand concentrations that may be required to meet detection sensitivity or complexation conditions, zonal migrations in ACE may, however, produce triangular peak shape, most often due to pronounced electromigration dispersion (EMD), and this may result in positively or negatively erroneous migration time assessments. In this work, EMD distorted triangular peak shapes obtained in the course of host-guest complexation studies were fitted with the Haarhoff-Van der Linde function, allowing better estimation of migration time. The model systems studied were those of beta-cyclodextrin and naproxen, 2-naphthalenesulfonate, or 1-adamantanecarboxylate. The impact of this correction on binding isotherms and binding constant evaluation was exemplified. Furthermore, in situations where the substrate concentration injected by far overtakes that of the ligand in the electrolyte, the interest in this peak shape correction was discussed in connection with the question of whether the free ligand concentration can be still considered equal to the ligand concentration introduced, a question that still remains under debate nowadays.

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.

Analysis of virtual two-dimensional gels based upon affinity capillary electrophoresis hyphenated to ion trap-mass spectrometry

Affinity capillary electrophoresis (ACE) is a robust tool for the study of noncovalent biomolecular interactions and to determine the binding constants. It is advantageous due to the speed of analysis, the high and reproducible separation efficiencies, the low consumption of analytes, the ability to study several interactions at the same time, and to cover a wide range of affinity. The use of an ion trap-mass spectrometer as a sensitive and specific detector, coupled on-line with a classical UV detector, permits extracting simultaneously the electropherograms corresponding to each ionic species. The mass spectra, acquired by scanning the results of a first separation due to ACE, were assimilated into a virtual two-dimensional (2-D) gel. We developed a software application, which was designed to create and analyze these virtual 2-D gels. The validity of this new analytical tool for probing biomolecular interactions has been demonstrated on mixtures of antibiotics of the vancomycin group and several dipeptide substrates. Using the dynamic equilibrium affinity electrophoresis approach, we have shown that molecular components interacting with a low affinity are easily located on the virtual 2-D gels, and that binding constants and stoichiometry of the interactions can be assessed. As the binding constants derived from ACE-electrospray ionization-mass spectrometry (ESI-MS) are unreliable, they must only be determined with the UV detector.

2002 W.A.E. McBryde Award Lecture — Affinity recognition, capillary electrophoresis, and laser-induced fluorescence polarization for ultrasensitive bioanalysis

The combination of affinity recognition, capillary electrophoresis (CE), laser-induced fluorescence (LIF), and fluorescence polarization for the ultrasensitive determination of compounds of biological interest is described. Competitive immunoassays using CE–LIF eliminate the need for fluorescently labeling trace analytes of interest and are particularly useful for determination of small molecules, such as cyclosporine, gentamicin, vancomycin, and digoxin. Fluorescence polarization allows for differentiation of the antibody-bound from the unbound small molecules. Noncompetitive affinity CE–LIF assays are shown to be highly effective in the determination of biomarkers for DNA damage and HIV-1 infection. An antibody (or aptamer) is used as a fluorescent probe to bind with a target DNA adduct (or the reverse transcriptase of the HIV-1 virus), with the fluorescent reaction products being separated by CE and detected by LIF. Aptamers are attractive affinity probes for protein analysis because of high affinity, high specificity, and the potential for a wide range of target proteins. Fluorescence polarization provides unique information for studying molecular interactions. Innovative integrations of these technologies will have broad applications ranging from cancer research, to biomedical diagnosis, to pharmaceutical and environmental analyses.Key words: capillary electrophoresis, laser-induced fluorescence, fluorescence polarization, immunoassay, affinity probes, antibodies, aptamers, DNA damage, toxins, therapeutic drugs.

Lipid vesicles in capillary electrophoretic techniques: characterization of structural properties and associated membrane-molecule interactions

This paper reviews the use of lipid vesicles as model membranes in capillary electrophoresis (CE). The history and utility of CE in the characterization of microparticles is summarized, focusing on the application of colloidal electromigration theories to lipid vesicles. For instance, CE experiments have been used to characterize the size, surface properties, enclosed volumes, and electrophoretic mobilities of lipid vesicles and of lipoprotein particles. Several techniques involving small molecules or macromolecules separated in the presence of lipid vesicles are discussed. Interactions between the analytes and the lipid vesicles - acting as a pseudostationary phase or coated stationary phase in electrokinetic chromatography (EKC) - can be used to obtain additional information on the characteristics of the vesicles and analytes, and to study the biophysical properties of membrane-molecule interactions in lipid vesicles and lipoproteins. Different methods of determining binding constants by EKC are reviewed, along with the relevant binding constant calculations and a discussion of the application and limitations of these techniques as they apply to lipid vesicle systems.

Determination of binding constants and stoichiometries for platinum anticancer drugs and serum transport proteins by capillary electrophoresis using the Hummel-Dreyer method

A CE method has been developed to evidence and quantitatively characterize the interaction between platinum-based antitumor drugs and human serum proteins. This method is a variant of affinity CE modified regarding both experimental setup and data treatment so as to measure the peaks (or vacancies) that correspond to the bound drug when it slowly binds to the protein. Using the formalism of the Hummel-Dreyer method and cisplatin and oxaliplatin as test compounds, a protocol for determining albumin and transferrin binding constants and stoichiometries, including (and distinguished by) 48 hours of incubation of the reaction mixture, was elaborated. Relative affinities of drugs toward different proteins in aqueous solution at physiological pH, chloride concentration, and temperature were compared in terms of overall binding constants and numbers of drug molecules attached to the protein. The results indicate that both platinum drugs bind to albumin more strongly than to transferrin, supporting the concept that the albumin fraction is a major drug supply route for chemotherapeutical needs. From a comparison with the binding parameters measured previously for cisplatin by other methods, conclusions were drawn about the validity of CE as a simple and convenient method for assaying protein-drug reactions with slow kinetics.

Affinity capillary electrophoresis on microchips

The present study shows that the application of the method of affinity capillary electrophoresis (ACE) to investigate interactions between ligands and their substrates can be realized on microchips. With ACE it is possible to characterize non-covalent molecular interactions (complexation and partition equilibria). Binding constants (K(B)) provide a measured value of the affinity of a ligand molecule to a substrate, which is basic information for the understanding of hormones, drugs and their targets, e.g. receptors in the human body. A microchip electrophoresis instrument equipped with a UV-detector and a home-built chip-station with electrochemical detection were used. ACE could be achieved with model solutions of neurotransmitters using sulfated beta-cyclodextrin (sCD) as substrate in a background buffer. This paper describes the advantages of microchip-ACE (MC-ACE) to traditional affinity capillary electrophoresis on a capillary. The results show that MC-ACE has great potential as a tool for fast scanning of interactions and to calculate binding constants of ligands with their substrates.

Using capillary electrophoresis with laser-induced fluorescence to study the interaction of green fluorescent protein-labeled calmodulin with Ca2+- and calmodulin-binding protein

A separation using capillary electrophoresis with laser-induced fluorescence (CE-LIF) was applied to the study of green fluorescent protein tagged calmoldulin (GFP-CaM) that was expressed from Escherichia coli and purified with Ni(2+)-nitrilotriacetate (Ni-NTA) resin column. It was found that GFP-CaM not only has good fluorescence properties under various conditions similar to GFP, but also retains its calcium-binding ability as the native CaM. GFP-CaM was separated and detected by CE-LIF within 10 min with a limit-of-detection (LOD) of 2 x 10(-10) M for an injection volume of 3 nl, higher than that of common chemical fluorescent-tagged protein method. The results indicated that, as a fluorescence probe, GFP could overcome the drawback of inefficient derivatization of chemical fluorescence probes. The interaction between the GFP-CaM and Ca(2+) was studied in detail using affinity capillary electrophoresis with laser-induced fluorescence and the dissociation constant (K(d)) between GFP-CaM and Ca(2+) was determined to be 1.2 x 10(-5), which is in good agreement with the literature values of untagged CaM (10(-6) to 10(-5)M) obtained by conventional method. As a preliminary application, the interaction between GFP-CaM and OsCBK was also investigated. The method makes it possible to screen the trace amounts of target proteins in crude extracts interacting with CaM under physiological conditions.