Volatile kinetic capillary electrophoresis for studies of protein-small molecule interactions

Study of molecular interactions by nonequilibrium capillary electrophoresis of equilibrium mixtures: Originations, developments, and applications

Molecular interactions play a vital role in regulating various physiological and biochemical processes in vivo. Kinetic capillary electrophoresis (KCE) is an analytical platform that offers significant advantages in studying the thermodynamic and kinetic parameters of molecular interactions. It enables the simultaneous analysis of these parameters within an interaction pattern and facilitates the screening of binding ligands with predetermined kinetic parameters. Nonequilibrium capillary electrophoresis of equilibrium mixtures (NECEEM) was the first proposed KCE method, and it has found widespread use in studying molecular interactions involving proteins/aptamers, proteins/small molecules, and peptides/small molecules. The successful applications of NECEEM have demonstrated its promising potential for further development and broader application. However, there has been a dearth of recent reviews on NECEEM. To address this gap, our study provides a comprehensive description of NECEEM, encompassing its origins, development, and applications from 2015 to 2022. The primary focus of the applications section is on aptamer selection and screening of small-molecule ligands. Furthermore, we discuss important considerations in NECEEM experimental design, such as buffer suitability, detector selection, and protein adsorption. By offering this thorough review, we aim to contribute to the understanding, advancement, and wider utilization of NECEEM as a valuable tool for studying molecular interactions and facilitating the identification of potential ligands and targets.

Transient Incomplete Separation Facilitates Finding Accurate Equilibrium Dissociation Constant of Protein-Small Molecule Complex

Current practical methods for finding the equilibrium dissociation constant, K_d , of protein-small molecule complexes have inherent sources of inaccuracy. Introduced here is "accurate constant via transient incomplete separation" (ACTIS), which appears to be free of inherent sources of inaccuracy. Conceptually, a short plug of the pre-equilibrated protein-small molecule mixture is pressure-propagated in a capillary, causing fast transient incomplete separation of the complex from the unbound small molecule. A superposition of signals from these two components is measured near the capillary exit and used to calculate a fraction of unbound small molecule, which, in turn, is used to calculate K_d . Herein the validity of ACTIS is proven theoretically, its accuracy is verified by computer simulation, and its practical use is demonstrated. ACTIS has the potential to become a reference-standard method for determining K_d  values of protein-small molecule complexes.

Capillary electrophoresis-based approaches for the study of affinity interactions combined with various sensitive and nontraditional detection techniques

Nearly all processes in living organisms are controlled and regulated by the synergy of many biomolecule interactions involving proteins, peptides, nucleic acids, nucleotides, saccharides, and small molecular weight ligands. There is growing interest in understanding them, not only for the purposes of interactomics as an essential part of system biology, but also in their further elucidation in disease pathology, diagnostics, and treatment. The necessity of detailed investigation of these interactions leads to the requirement of laboratory methods characterized by high efficiency and sensitivity. As a result, many instrumental approaches differing in their fundamental principles have been developed, including those based on capillary electrophoresis. Although capillary electrophoresis offers numerous advantages for such studies, it still has one serious limitation, its poor concentration sensitivity with the most commonly used detection method-ultraviolet-visible spectrometry. However, coupling capillary electrophoresis with a more sensitive detector fulfils the above-mentioned requirement. In this review, capillary electrophoresis combined with fluorescence, mass spectrometry, and several nontraditional detection techniques in affinity interaction studies are summarized and discussed, together with the possibility of conducting these measurements in microchip format.

Binding assay for low molecular weight analytes based on reflectometry of absorbing molecules in porous substrates

Small molecule sensing is of great importance in pharmaceutical research. While there exist well established screening methods such as EMSA (electrophoretic motility shift assay) or biointeraction chromatography to report on successful binding interactions, there are only a few techniques that allow studying and quantifying the interaction of low molecular weight analytes with a binding partner directly. We report on a binding assay for small molecules based on the reflectivity change of a porous transparent film upon immobilisation of an absorbing substance on the pore walls. The porous matrix acts as a thin optical transparent film to produce interference fringes and accumulates molecules at the inner wall to amplify the sensor response. The benefits and limits of the assay are demonstrated by investigating the binding of biotin labelled with an atto dye to avidin physisorbed within an anodic aluminium oxide membrane.

Terminal protection of small molecule-linked DNA for small molecule-protein interaction assays

Methods for the detection of specific interactions between diverse proteins and various small-molecule ligands are of significant importance in understanding the mechanisms of many critical physiological processes of organisms. The techniques also represent a major avenue to drug screening, molecular diagnostics, and public safety monitoring. Terminal protection assay of small molecule-linked DNA is a demonstrated novel methodology which has exhibited great potential for the development of simple, sensitive, specific and high-throughput methods for the detection of small molecule–protein interactions. Herein, we review the basic principle of terminal protection assay, the development of associated methods, and the signal amplification strategies adopted for performance improving in small molecule–protein interaction assay.

Recent developments in capillary and microchip electroseparations of peptides (2011-2013)

The review presents a comprehensive survey of recent developments and applications of capillary and microchip electroseparation methods (zone electrophoresis, ITP, IEF, affinity electrophoresis, EKC, and electrochromatography) for analysis, isolation, purification, and physicochemical and biochemical characterization of peptides. Advances in the investigation of electromigration properties of peptides, in the methodology of their analysis, including sample preseparation, preconcentration and derivatization, adsorption suppression and EOF control, as well as in detection of peptides, are presented. New developments in particular CE and CEC modes are reported and several types of their applications to peptide analysis are described: conventional qualitative and quantitative analysis, determination in complex (bio)matrices, monitoring of chemical and enzymatical reactions and physical changes, amino acid, sequence and chiral analysis, and peptide mapping of proteins. Some micropreparative peptide separations are shown and capabilities of CE and CEC techniques to provide relevant physicochemical characteristics of peptides are demonstrated.