Detection of Aequorea victoria green fluorescent protein by capillary electrophoresis laser induced fluorescence detection

Combination of on-chip field amplification and bovine serum albumin sweeping for ultrasensitive detection of green fluorescent protein

We report a highly effective on-chip preconcentration method by combining field-amplified sample injection (FASI) and bovine serum albumin (BSA) sweeping for ultrasensitive detection of green fluorescent protein (GFP) on a simple cross-channel microchip device. With the formation of a stagnant sample/running buffer boundary by balancing the hydrodynamic flow and the electro-osmotic flow (EOF), GFP molecules can be continuously injected into the sample loading channel and stacked. We have also demonstrated that BSA is a very effective pseudo-stationary phase for sweeping concentration of proteins in comparison to the commonly used micelles. The combination of FASI and BSA sweeping yields a concentration factor of 3570 and a limit of detection of 8.4 pM for GFP. Using this method, we have separated GFP and GFP-insulin-like growth factor-I (GFP-IGF-I) fusion protein. The entire assay (GFP concentration, matrix elimination, and electrophoretic separation) can be completed within <5 min. Furthermore, we have successfully applied this method for the detection of GFP expression of E. coli cells and the GFP content in single E. coli cells.

Biarsenical-tetracysteine motif as a fluorescent tag for detection in capillary electrophoresis

Biarsenical dyes complexed to tetracysteine motifs have proven to be highly useful fluorescent dyes in labeling specific cellular proteins for microscopic imaging. Their many advantages include membrane permeability, relatively small size, stoichiometric labeling, high affinity, and an assortment of excitation/emission wavelengths. The goal of the current study was to determine whether the biarsenical labeling scheme could be extended to fluorescent detection of analytes in capillary electrophoresis. Recombinant protein or synthesized peptides containing the optimized tetracysteine motif "-C-C-P-G-C-C-" were labeled with biarsenical dyes and then analyzed by micellar electrokinetic capillary chromatography (MEKC). The biarsenical-tetracysteine complex was stable and remained fluorescent under standard MEKC conditions for peptide and protein separations. The detection limit following electrophoresis in a capillary was less than 3 x 10(-20) mol with a simple laser-induced fluorescence system. A mixture of multiple biarsenical-labeled peptides and a protein were easily resolved. Demonstrating that the label did not interfere with bioactivity, a peptide-based enzyme substrate conjugated to the tetracysteine motif and labeled with a biarsenical dye retained its ability to be phosphorylated by the parent kinase. The feasibility of using this label for chemical cytometry experiments was shown by intracellular labeling and subsequent analysis of a recombinant protein possessing the tetracysteine motif expressed in living cells. The extension of the biarsenical-tetracysteine tag to fluorescent labeling of peptides and proteins in chemical separations is a valuable addition to biochemical and cell-based investigations.

CSE-MECC two-dimensional capillary electrophoresis analysis of proteins in the mouse tumor cell (AtT-20) homogenate

Two-dimensional capillary electrophoresis was used for the separation of proteins and biogenic amines from the mouse AtT-20 cell line. The first-dimension capillary contained a TRIS-CHES-SDS-dextran buffer to perform capillary sieving electrophoresis, which is based on molecular weight of proteins. The second-dimension capillary contained a TRIS-CHES-SDS buffer for micel1ar electrokinetic capillary chromatography. After a 61 seconds preliminary separation, fractions from the first-dimension capillary were successively transferred to the second-dimension capillary, where they further separated by MECC. The two-dimensional separation required 60 minutes.

LIF detection of peptides and proteins in CE

CE- and microchip-based separations coupled with LIF are powerful tools for the separation, detection and determination of biomolecules. CE with certain configurations has the potential to detect a small number of molecules or even a single molecule, thanks to the high spatial coherence of the laser source which permits the excitation of very small sample volumes with high efficiency. This review article discusses the use of LIF detection for the analysis of peptides and proteins in CE. The most common laser sources, basic instrumentation, derivatization modes and set-ups are briefly presented and special attention is paid to the different fluorogenic agents used for pre-, on- and postcapillary derivatization of the functional groups of these compounds. A table summarizing major applications of these derivatization reactions to the analysis of peptides and proteins in CE-LIF and a bibliography with 184 references are provided which covers papers published to the end of 2005.

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.

All solid-state GFP sensor

An all-solid-state green fluorescent protein (GFP) sensor for GFP measurement was developed. It is immune to interference from ambient light and works with standard flow-through cuvettes. The sensor is practically insensitive to the scattered excitation light encountered in microbial suspensions. It has a range of 0.0002-1 g/L (7.4 x 10(-9) - 3.7 x 10(-5) M) with limit of detection 0.00019 g/L (7.0 x 10(-9) M). The sensor could be used with a UV or blue light emitting diode (LED) as a light source, depending on required sensitivity, selectivity, and background levels. Its very low cost makes it useful in a variety of applications. This article describes the construction and validation of the sensor both off- and on-line in fermentation processes.

Green fluorescent protein in Saccharomyces cerevisiae: real-time studies of the GAL1 promoter

Green fluorescent protein (GFP) was used to study the regulation of the galactose-inducible GAL1 promoter in yeast Saccharomyces cerevisiae strains. GFP was cloned into the pGAL110 vector and transformed into the yeast strains. Time course studies comparing culture fluorescence intensity and GFP concentration were conducted along with on-line monitoring of GFP expression. Our results demonstrated that GFP fluorescence could be used as a quantifiable on-line reporter gene in yeast strains. The effect of an integrated GAL10p-GAL4 transcription cassette was investigated. Induction time studies showed that there was no significant difference in GFP expression level by adding galactose at different culture times. A wide range of galactose concentrations was used to study the initial galactose concentration effect on GFP expression kinetics. A minimum of 0.05 g/L galactose doubled the GFP fluorescence signal as compared to the control, whereas 0.1 g/L gave the highest specific GFP yield. A simple analytical model was proposed to describe GFP expression kinetics based on the experimental results. In addition, this GFP-based approach was shown to have potential use for high-throughput studies. The use of GFP as a generic tool provided important insights to the GAL expression system and has great potential for further process optimization applications.

Recent developments in capillary zone electrophoresis of proteins

This review article with 125 references describes recent developments in capillary zone electrophoresis of proteins. It encompasses approximately the last two years, from the previous review (V. Dolník, Electrophoresis 1997, 18, 2353-2361) through Spring 1999. Topics covered include modeling of the electrophoretic properties of proteins, sample preconcentration and derivatization, wall coatings, improving selectivity, special detection techniques, and applications.

Expression and analysis of green fluorescent proteins in human embryonic kidney cells by capillary electrophoresis

The green fluorescent protein (GFP) has attracted much interest as a reporter for gene expression. In this paper, application of capillary electrophoresis with laser-induced fluorescent (CE-LIF) for quantitation of green fluorescence protein in cellular extracts and single cells is investigated. The S65T mutant form of GFP protein was successfully expressed in human embryonic kidney (HEK293) cells, and its production was confirmed by fluorescence microscopy and CE-LIF. The mass limit of detection for the mutant S65T was 5.3 x 10(-20) mol, which was better than that for the wild-type GFP by a factor of six. Detection of a small amount of GFP is difficult by conventional techniques such as fluorescent microscopy due to interference from cell autofluorescence at low GFP concentrations. The HEK293 cells were transfected with the GFP plasmid that produced S65T-GFP. Transient production of S65T protein was detected 2 h after the transfection and reached a maximum after 48 h. The protein concentration began to decrease significantly after 96 h. Single cell analysis of HEK293 cells after transfection with GFP plasmid indicate a nonuniform production of S65T-GFP protein among cells.

Picomolar analysis of proteins using electrophoretically mediated microanalysis and capillary electrophoresis with laser-induced fluorescence detection

We report a method for the analysis of picomolar concentration proteins using electrophoretically mediated microanalysis (EMMA) to label proteins on-column with a fluorogenic reagent. Labeling is followed by capillary zone electrophoresis separation and postcolumn detection based on laser-induced fluorescence. The method provides a concentration detection limit (3 sigma) of 3 x 10(-13) M for conalbumin. The method provides separation efficiency of 300,000 theoretical plates. Protein extract from a human colon adenocarcinoma cell line generated a dozen major components and many minor components in a 12-min separation; the protein extract from 2.5 cells was used for this analysis. When compared to UV absorbance detection, the EMMA method provides 7,000,000-fold improvement in detection limit.