Determination of endogenous extracellular signal-regulated protein kinase by microchip capillary electrophoresis

Electrochemical biosensors based on peptide-kinase interactions at the kinase docking site

Kinases are important cancer biomarkers and are conventionally detected based on their catalytic activity. Kinases regulate cellular activities by phosphorylation of motif-specific multiple substrate proteins, resulting in a lack of selectivity of activity-based kinase biosensors. We present an alternative approach of sensing kinases based on the interactions of their allosteric docking sites with a specific partner protein. The new approach was demonstrated for the ERK2 kinase and its substrate ELK-1. A peptide derived from ELK-1 was bound to a gold electrode and ERK2 sensing was performed by electrochemical impedance spectroscopy. We performed a detailed analysis of the interaction between the ELK-1 peptide and the kinase on gold surfaces. Atomic force microscopy, variable angle spectroscopic ellipsometry, X-ray Photoelectron Spectroscopy, and polarization modulation IR reflection-absorption spectroscopy analysis of the gold surface revealed the adsorbed layer of the ERK2 on the peptide monolayer. The sensors showed a high level of target selectivity for ERK2 compared to the p38γ kinase and BSA. ERK2 was detected in its cellular concentration range, 0.5-2.0 μM, and the limit of detection was calculated to be 0.35 μM. Using the flexibility of peptide design, our method is generic for developing sensitive and substrate-specific biosensors and other disease-related enzymes based on their interactions.

A lab-on-a-chip for monolith-based preconcentration and electrophoresis separation of phosphopeptides

A real μTAS integrating monolith-based IMAC enrichment, electrophoresis separation and fluorescence detection of phosphopeptides is reported for the first time.

Capillary electrophoresis of signaling molecules

The emerging field of quantitative systems biology uses high-throughput bioanalytical measurements to gain a deeper understanding of biological phenomena. With the advent of instrumentation platforms, capillary electrophoresis spans a very wide range of biological applications. This short article focuses on the exploitation of capillary electrophoresis for the systems-level analysis of cell signaling molecules.

Recent developments in optical detection methods for microchip separations

This paper summarizes the features and performances of optical detection systems currently applied in order to monitor separations on microchip devices. Fluorescence detection, which delivers very high sensitivity and selectivity, is still the most widely applied method of detection. Instruments utilizing laser-induced fluorescence (LIF) and lamp-based fluorescence along with recent applications of light-emitting diodes (LED) as excitation sources are also covered in this paper. Since chemiluminescence detection can be achieved using extremely simple devices which no longer require light sources and optical components for focusing and collimation, interesting approaches based on this technique are presented, too. Although UV/vis absorbance is a detection method that is commonly used in standard desktop electrophoresis and liquid chromatography instruments, it has not yet reached the same level of popularity for microchip applications. Current applications of UV/vis absorbance detection to microchip separations and innovative approaches that increase sensitivity are described. This article, which contains 85 references, focuses on developments and applications published within the last three years, points out exciting new approaches, and provides future perspectives on this field.

On-line sample preconcentration using field-amplified stacking injection in microchip capillary electrophoresis

Previous reports describing sample stacking on microchip capillary electrophoresis (microCE) have regarded the microchip channels as a closed system and treated the bulk flow as in traditional capillary electrophoresis. This work demonstrates that the flows arising from the intersection should be investigated as an open system. It is shown that the pressure-driven flows into or from the branch channels due to bulk velocity mismatch in the main channel should not be neglected but can be used for liquid transportation in the channels. On the basis of these concepts, a sample preconcentration scheme was developed in a commercially available single-cross glass chip for microCE. Similar to field-amplified stacking injection in traditional CE, a low conductivity sample buffer plug was introduced into the separation channel immediately before the negatively charged analyte molecules were injected. The detection sensitivity was improved by 94-, 108-, and 160-fold for fluorescein-5-isothiocyanate, fluorescein disodium, and 5-carboxyfluorescein, respectively, relative to a traditional pinched injection. The calibration curves for fluorescein and 5-carboxyfluorescein demonstrated good linearity in the concentration range (1-60 nM) investigated with acceptable reproducibility of migration time and peak height and area ratios (4-5% RSD). This preconcentration scheme will be of particular significance to the practical use of microCE in the emerging miniaturized analytical instrumentation.

Determination of enzymatic activity by capillary electrophoresis

Enzymes are biological catalysts that play an important role in biochemical reactions necessary for normal growth, maturation and reproduction through whole live world. Their accurate quantitation in biological samples is important in many fields of biochemistry, not only in routine biochemistry and in fundamental research, but also in clinical and pharmacological research and diagnosis. Since the direct measurement of enzymes by masses is impossible, they must be quantified by their catalytic activities. Many different methods have been applied for this purpose so far. Although photometric methods are undoubtedly the most frequently used, separation methods will further gain their position in this field. The article reviews different possibilities for the assay of enzymatic activity by means of capillary electrophoresis (CE). Both the off-line and on-line enzyme assays based on CE are discussed.

Capillary electrophoresis of proteins 2003-2005

This review article with 304 references describes recent developments in CE of proteins, and covers the two years since the previous review (Hutterer, K., Dolník, V., Electrophoresis 2003, 24, 3998-4012) through Spring 2005. It covers topics related to CE of proteins, including modeling of the electrophoretic migration of proteins, sample pretreatment, wall coatings, improving separation, various forms of detection, special electrophoretic techniques such as affinity CE, CIEF, and applications of CE to the analysis of proteins in real-world samples including human body fluids, food and agricultural samples, protein pharmaceuticals, and recombinant protein preparations.

Estimation of logPow values for neutral and basic compounds by microchip microemulsion electrokinetic chromatography with indirect fluorimetric detection (μMEEKC-IFD)

Microchip microemulsion electrokinetic chromatography with indirect fluorimetric detection (muMEEKC-IFD) was used to obtain logP octanol/water (logP(ow)) values for neutral and basic compounds. Six compounds, with logP(ow) values between 0.38 and 5.03, were used to create a calibration curve relating the log of retention factors (logk) obtained from muMEEKC-IFD with the known logP(ow) values. The logP(ow) values for six additional compounds were determined using the logk values obtained by muMEEKC-IFD and the linear relationship between logP(ow) and logk established for the standard compounds. The muMEEKC-IFD buffer was composed of 50 mM 3-[cyclohexylamino]-1-propane-sulfonic acid (CAPS) buffer (pH 10.4) containing 1.2% n-heptane (v/v), 2% sodium dodecylsulfate (w/v), 8% 1-butanol (v/v) and 4 microM 5-carboxytetramethyl-rhodamine (TAMRA) as the fluorophore probe for indirect detection. The muMEEKC-IFD provided an accurate method for estimating logP(ow) values and also a means for analyzing compounds that are non-fluorescent.

Applications of Fluorescent Polymer Superquenching to High Throughput Screening Assays for Protein Kinases

Protein kinases are involved in the regulation of cellular metabolism, growth, differentiation, and proliferation. Aberrations in their function can lead to diseases such as cancer and inflammation. Protein kinases are therefore possible targets for drug therapies. To address the need for high throughput screening of potential inhibitors, QTL has developed a homogeneous and robust kinase assay for use in multiwell plate format. The QTL Lightspeed fluorescence superquenching-based kinase assays do not require specialized equipment, nor do they involve the use of radioactive hazardous materials or antibodies. QTL Lightspeed kinase assays directly measure the enzymatic activity of the target and do not involve secondary (detector) enzyme. In this article, we compare QTL Lightspeed protein kinase assays using Protein Kinase A, Protein Kinase Balpha/Akt1, and ribosomal S6 kinase-2 as examples with other commercially available kinase kits. Our data show that QTL Lightspeed kinase assays offer significant advantages over the current commercial kits in terms of both sensitivity and performance. The QTL Lightspeed kinase assay also offers a kinetic assay mode where the substrate phosphorylation can be monitored in real-time.