Microchip CGE linked to immunoprecipitation as an alternative to Western blotting

Automated Capillary Electrophoresis Immunoblot for the Detection of Alpha-Synuclein in Mouse Tissue

Background

Alpha-synuclein (aSyn) is a key player in neurodegenerative diseases such as Parkinson's disease (PD), dementia with Lewy bodies, or multiple system atrophy. aSyn is expressed throughout the brain, and can also be detected in various peripheral tissues. In fact, initial symptoms of PD are non-motoric and include autonomic dysfunction, suggesting that the periphery might play an important role in early development of the disease. aSyn is expressed at relatively low levels in non-central tissues, which brings challenges for its detection and quantification in different tissues.

Objective

Our goal was to assess the sensitivity of aSyn detection in central and peripheral mouse tissues through capillary electrophoresis (CE) immunoblot, considering the traditional SDS-PAGE immunoblot as the current standard.

Methods

Tissues from central and non-central origin from wild type mice were extracted, and included midbrain, inner ear, and esophagus/stomach. aSyn detection was assessed through immunoblotting using Simple Western size-based CE and SDS-PAGE.

Results

CE immunoblots show a consistent detection of aSyn in central and peripheral tissues. Through SDS-PAGE, immunoblots revealed a reliable signal corresponding to aSyn, particularly following membrane fixation.

Conclusion

Our results suggest a reliable detection of aSyn in central and peripheral tissues using the CE Simple Western immunoblot system. These observations can serve as preliminary datasets when aiming to formally compare CE with SDS-PAGE, as well as for further characterization of aSyn using this technique.

Fast Immunoassay for Microfluidic Western Blotting by Direct Deposition of Reagents onto Capture Membrane

Western blotting is a widely used protein assay platform, but the technique requires long analysis times and multiple manual steps. Microfluidic systems are currently being explored for increased automation and reduction of analysis times, sample volumes, and reagent consumption for western blots. Previous work has demonstrated that proteins separated by microchip electrophoresis can be captured on membranes by dragging the microchip outlet across the membrane. This process reduces the separation and transfer time of a western blot to a few minutes. To further improve the speed and miniaturization of a complete western blot, a microscale immunoassay with direct deposition of immunoassay reagents has been developed. Flow deposition of antibodies is used to overcome diffusion limited binding kinetics so that the entire immunoassay can be completed in 1 h with detection sensitivity comparable to incubation steps requiring 20 h. The use of low microliter/min flow rates with antibody reagents applied directly and locally to the membrane where the target proteins have been captured, reduced antibody consumption ~30-fold. The complete western blot was applied to the detection of GAPDH and β-Tubulin from A431 cell lysate.

Protein purification and analysis: next generation Western blotting techniques

INTRODUCTION

Western blotting is one of the most commonly used techniques in molecular biology and proteomics. Since western blotting is a multistep protocol, variations and errors can occur at any step reducing the reliability and reproducibility of this technique. Recent reports suggest that a few key steps, such as the sample preparation method, the amount and source of primary antibody used, as well as the normalization method utilized, are critical for reproducible western blot results. Areas covered: In this review, improvements in different areas of western blotting, including protein transfer and antibody validation, are summarized. The review discusses the most advanced western blotting techniques available and highlights the relationship between next generation western blotting techniques and its clinical relevance. Expert commentary: Over the last decade significant improvements have been made in creating more sensitive, automated, and advanced techniques by optimizing various aspects of the western blot protocol. New methods such as single cell-resolution western blot, capillary electrophoresis, DigiWest, automated microfluid western blotting and microchip electrophoresis have all been developed to reduce potential problems associated with the western blotting technique. Innovative developments in instrumentation and increased sensitivity for western blots offer novel possibilities for increasing the clinical implications of western blot.

From little helpers to automation

Western blot technology has continually evolved to enhance sensitivity, speed, and ease of operation. For enhancing awareness to these developments, this brief review outlines a representative selection of methods and devices, many of which are commercial products. In particular, the steps taken towards partial and full automation of western blotting are addressed.

Qualitative and quantitative evaluation of Simon™, a new CE-based automated Western blot system as applied to vaccine development

Many CE-based technologies such as imaged capillary IEF, CE-SDS, CZE, and MEKC are well established for analyzing proteins, viruses, or other biomolecules such as polysaccharides. For example, imaged capillary isoelectric focusing (charge-based protein separation) and CE-SDS (size-based protein separation) are standard replacement methods in biopharmaceutical industries for tedious and labor intensive IEF and SDS-PAGE methods, respectively. Another important analytical tool for protein characterization is a Western blot, where after size-based separation in SDS-PAGE the proteins are transferred to a membrane and blotted with specific monoclonal or polyclonal antibodies. Western blotting analysis is applied in many areas such as biomarker research, therapeutic target identification, and vaccine development. Currently, the procedure is very manual, laborious, and time consuming. Here, we evaluate a new technology called Simple Western™ (or Simon™) for performing automated Western analysis. This new technology is based on CE-SDS where the separated proteins are attached to the wall of capillary by a proprietary photo activated chemical crosslink. Subsequent blotting is done automatically by incubating and washing the capillary with primary and secondary antibodies conjugated with horseradish peroxidase and detected with chemiluminescence. Typically, Western blots are not quantitative, hence we also evaluated the quantitative aspect of this new technology. We demonstrate that Simon™ can quantitate specific components in one of our vaccine candidates and it provides good reproducibility and intermediate precision with CV <10%.

Rapid detection and quantification of specific proteins by immunodepletion and microfluidic separation

Conventional immunoblotting techniques are labor intensive, time consuming and rely on the elution of target protein after depletion. Here we describe a new method for detection and quantification of proteins, independent of washing and elution. In this method, the target protein is first captured by immunodepletion with antibody-coated microbeads. In the second step, both the supernatant after immunodepletion and the untreated protein sample are directly analyzed by microfluidic electrophoresis without further processing. Subsequently, the detection and quantification are performed by comparing the electropherograms of these two samples. This method was tested using an Escherichia coli lysate with a FLAG-tagged protein and anti-FLAG magnetic beads. An incubation of as short as one min was sufficient for detectable depletion (66%) by microchip electrophoresis. Longer incubation (up to 60 min) resulted in more depletion of the target band (82%). Our results show that only 19% of the target is recovered after elution from the beads. By eliminating multiple wash and elution steps, our method is faster, less labor intensive, and highly reproducible. The target protein can still be easily identified even in the case of nonspecific binding at low concentrations. This work highlights the advantages of integrating immunodepletion techniques on a microfluidic platform.

Western blotting via proximity ligation for high performance protein analysis

Western blotting is a powerful and widely used method, but limitations in detection sensitivity and specificity, and dependence upon high quality antibodies to detect targeted proteins, are hurdles to overcome. The in situ proximity ligation assay, based on dual antibody recognition and powerful localized signal amplification, offers increased detection sensitivity and specificity, along with an ability to identify complex targets such as phosphorylated or interacting proteins. Here we have applied the in situ proximity ligation assay mechanism in Western blotting. This combination allowed the use of isothermal rolling circle amplification of DNA molecules formed in target-specific ligation reaction, for 16-fold or greater increase in detection sensitivity. The increased specificity because of dual antibody recognition ensured highly selective assays, detecting the specific band when combinations of two cross-reactive antitubulin antibodies were used (i.e. both producing distinct nonspecific bands in traditional Western blotting). We also demonstrated detection of phosphorylated platelet-derived growth factor receptor β by proximity ligation with one antibody directed against the receptor and another directed against the phosphorylated tyrosine residue. This avoided the need for stripping and re-probing the membrane or aligning two separate traditional blots. We demonstrate that the high-performance in situ proximity ligation-based Western blotting described herein is compatible with detection via enhanced chemiluminescence and fluorescence detection systems, and can thus be readily employed in any laboratory.