Pyrogallol red-molybdate: a reversible, metal chelate stain for detection of proteins immobilized on membrane supports

Total protein assay by PCA-based RGB-spectrum conversion methods with smartphone-acquired digital images

Total protein concentrations in the aqueous solutions were determined from the absorption spectra reproduced from smartphone-captured digital color images. We employed two different procedures for protein determination: the pyrogallol red molybdate method and Bradford's method. The principal-component-analysis-based reproduction process, which was previously reported by our research group, enabled the conversion of RGB values to score values for a linear combination of loading vectors to generate reproduced absorption spectra. The reproduced spectra were identical to those measured using a commercially available spectrophotometer. The total protein assays of commercial soymilk and human serum samples were carried out with both coloration reagents, and the obtained results were in good agreement with those attained using a conventional spectrophotometer. These results show that the proposed method enables smartphone-based ratiometric analysis of real samples without requiring any monochromating equipment.

Solid-Liquid Europium Ion Extraction via Phosphonic Acid-Functionalized Polyvinylidene Fluoride Siloxanes

Novel triethoxysilane and dimethyl phosphonate functional vinylidene fluoride (VDF)-containing terpolymers, for potential applications in Eu ion extraction from water, were produced by conventional radical terpolymerization of VDF with vinyltriethoxylsilane (VTEOS) and vinyldimethylphosphonate (VDMP). Although initial attempts for the copolymerization of VTEOS and VDMP failed, the successful terpolymerization was initiated by peroxide to lead to multiple poly(VDF-ter-VDMP-ter-VTEOS) terpolymers, that had different molar percentages of VDF (70–90 mol.%), VTEOS (5–20 mol.%) and VDMP (10 mol.%) in 50–80% yields. The obtained terpolymers were characterized by ¹H, ¹⁹F, ²⁹Si and ³¹P NMR spectroscopies. The crosslinking of such resulting poly(VDF-ter-VDMP-ter-VTEOS) terpolymers was achieved by hydrolysis and condensation (sol–gel process) of the triethoxysilane groups in acidic media, to obtain a 3D network, which was analyzed by solid state ²⁹Si and ³¹P NMR spectroscopies, TGA and DSC. The thermal stability of the terpolymers was moderately high (up to 300 °C under air), whereas they display a slight increase in their crystallinity-rate from 9.7% to 12.1% after crosslinking. Finally, the dimethyl phosphonate functions were hydrolyzed into phosphonic acid successfully, and the europium ion extraction capacity of terpolymer was studied. The results demonstrated a very high removal capacity of Eu(III) ions from water, up to a total removal at low concentrations.

Tubulin or Not Tubulin: Heading Toward Total Protein Staining as Loading Control in Western Blots

Western blotting is an analytical method widely used for detecting and (semi-)quantifying specific proteins in given samples. Western blots are continuously applied and developed by the protein community. This review article focuses on a significant, but not yet well-established, improvement concerning the internal loading control as a prerequisite to accurately quantifying Western blots. Currently, housekeeping proteins (HKPs) like actin, tubulin, or GAPDH are often used to check for equal loading or to compensate potential loading differences. However, this loading control has multiple drawbacks. Staining of the total protein on the blotting membrane has emerged as a better loading control. Total protein staining (TPS) represents the actual loading amount more accurately than HKPs due to minor technical and biological variation. Further, the broad dynamic range of TPS solves the issue of HKPs that commonly fail to show loading differences above small loading amounts of 0.5-10 μg. Although these and further significant advantages have been demonstrated over the past 10 years, only a small percentage of laboratories take advantage of it. The objective of this review article is to collect and compare information about TPS options and to invite users to reconsider their applied loading control. Nine benefits of TPS are discussed and seven different variants are critically evaluated by comparing technical details. Consequently, this review article offers an orientation in selecting the appropriate staining type. I conclude that TPS should be the preferred loading control in future Western blot approaches.

Protein stains for proteomic applications: which, when, why?

This review recollects literature data on sensitivity and dynamic range for the most commonly used colorimetric and fluorescent dyes for general protein staining, and summarizes procedures for the most common PTM-specific detection methods. It also compiles some important points to be considered in imaging and evaluation. In addition to theoretical considerations, examples are provided to illustrate differential staining of specific proteins with different detection methods. This includes a large body of original data on the comparative evaluation of several pre- and post-electrophoresis stains used in parallel on a single specimen, horse serum run in 2-DE (IPG-DALT). A number of proteins/protein spots are found to be over- or under-revealed with some of the staining procedures.

Microwave-Enhanced Ink Staining for Fast and Sensitive Protein Quantification in Proteomic Studies

A novel microwave-enhanced ink staining method was developed for rapid and sensitive estimation of protein content in sample buffers containing chaotropes, dyes, detergents, and reducing agents. Dye-based Blue-Black ink was used to quantitatively visualize proteins spotted on a nitrocellulose membrane. The total staining time was greatly reduced to 3 min by brief exposure to microwave radiation. The stained membrane was washed with distilled water, baked in a microwave oven for complete desiccation, transparentized with mineral oil, and documented by a desktop scanner or densitometer. Only 1 microL of protein sample (protein solubilized in SDS-PAGE sample buffer or IEF rehydration buffer) was used for protein spotting. The novel solid-phase protein assay gives a 500-fold dynamic range from 19.5 to 10000 ng/microL and can be scaled up for high-throughput protein quantification analysis. The fast, sensitive and low-cost microwave-enhanced ink staining procedure is ideal for protein quantification in proteomic analysis.

NFkappaB translocation in human microvessel endothelial cells using a four-compartment subcellular protein redistribution assay

Protein distribution profiles may be used to characterize both physiological and pathophysiological cellular changes, but rigorous biochemical assays for measuring such movements are lacking. This paper reports on a protein redistribution assay that combines reversible metal chelate-based total protein detection with a four-fraction subcellular detergent fractionation procedure. TNF-alpha stimulated cultured human omental microvessel endothelial cells are fractionated into cytosol, membrane/organelle, nuclear (envelope and associated), and cytoskeletal/DNA compartments. Protein fractions are separated electrophoretically and electroblotted or slot-blotted onto PVDF membranes without electrophoretic separation. A key feature is that total protein is measured and analyzed directly on the resultant PVDF membrane, using a Ferrozine/ferrous metal-chelate stain, without the added step of a prior solution-phase protein assay. As a result, factors that may adversely affect NFkappaB quantification, such as saturation of the solid-support membrane, are rigorously evaluated and controlled. Following removal of the Ferrozine/ferrous total protein stain, NFkappaB distribution is determined via standard immunodetection procedures. This assay reveals a new level of complexity regarding NFkappaB distribution and translocation. NFkappaB is shown to translocate from the cytosol to the membrane/organelle and cytoskeletal/DNA fractions, whereas trace levels of NFkappaB are observed in the nuclear (envelope and associated) fraction. Dose-curve analysis reveals that the response is initiated at 10 U/ml of TNF-alpha, plateaus at approximately 1000 U/ml, and remains essentially constant up to 2000 U/ml. Time-course analysis demonstrates a measurable response as early as 5 min and a peak response at approximately 30 min, after which the distribution begins to return to baseline. The assay should provide a valuable tool for rapid evaluation and mechanistic studies of NFkappaB redistribution.

A thousand points of light: the application of fluorescence detection technologies to two-dimensional gel electrophoresis and proteomics

As proteomics evolves into a high-throughput technology for the study of global protein regulation, new demands are continually being placed upon protein visualization and quantitation methods. Chief among these are increased detection sensitivity, broad linear dynamic range and compatibility with modern methods of microchemical analyses. The limitations of conventional protein staining techniques are increasingly being encountered as high sensitivity electrophoresis methods are interfaced with automated gel stainers, image analysis workstations, robotic spot excision instruments, protein digestion work stations, and mass spectrometers. Three approaches to fluorescence detection of proteins in two-dimensional (2-D) gels are currently practiced: covalent derivatization of proteins with fluorophores, intercalation of fluorophores into the sodium dodecyl sulfate (SDS) micelle, and direct electrostatic interaction with proteins by a Coomassie Brilliant Blue-type mechanism. This review discusses problems encountered in the analysis of proteins visualized with conventional stains and addresses advances in fluorescence protein detection, including immunoblotting, as well as the use of charge-coupled device (CCD) camera-based and laser-scanner-based image acquisition devices in proteomics.

Direct Blue 71 staining of proteins bound to blotting membranes

A sensitive staining method for protein blots using Direct Blue 71 is described. It is based on the selective binding of dye molecules to proteins in acidic solution and produces bluish violet colored bands. It is a simple and rapid procedure, involving only staining and rinsing steps that occur within 7 min. The sensitivity of this method is 5-10 ng of protein on nitrocellulose (NC) and 10-20 ng on polyvinylidene difluoride (PVDF), which is tenfold better than that of the commonly used Ponceau S staining. Moreover, the staining is reversible for subsequent immunostaining, without impairing immunoreactivity. To remove the dye from the developed bands, changes in pH and hydrophobicity of the solvent are required. Due to its sensitivity, rapidity, simplicity, and low cost, this stain may be more practical than other dye-based stains or metal-based stains for routine laboratory purposes.

A luminescent ruthenium complex for ultrasensitive detection of proteins immobilized on membrane supports

SYPRO Ruby protein blot stain provides a sensitive, gentle, fluorescence-based method for detecting proteins on nitrocellulose or polyvinylidene difluoride (PVDF) membranes. SYPRO Ruby dye is a permanent stain composed of ruthenium as part of an organic complex that interacts noncovalently with proteins. Stained proteins can be excited by ultraviolet light of about 302 nm or with visible light of about 470 nm. Fluorescence emission of the dye is approximately 618 nm. The stain can be visualized using a wide range of excitation sources utilized in image analysis systems including a UV-B transilluminator, 488-nm argon-ion laser, 532-nm yttrium-aluminum-garnet (YAG) laser, blue fluorescent light bulb, or blue light-emitting diode (LED). The detection sensitivity of SYPRO Ruby protein blot stain (0.25-1 ng protein/mm(2)) is superior to that of amido black, Coomassie blue, and india ink staining and nearly matches colloidal gold staining. SYPRO Ruby protein blot stain visualizes proteins more rapidly than colloidal gold stain and the linear dynamic range is more extensive. Unlike colloidal gold stain, SYPRO Ruby protein blot stain is fully compatible with subsequent biochemical applications including colorimetric and chemiluminescent immunoblotting, Edman-based sequencing and mass spectrometry.

Precipitation of dilute chromatographic samples (ng/ml) containing interfering substances for SDS-PAGE

SDS-PAGE of chromatographic fractions requires prior removal of salts, detergents, denaturants, or organic solvents which may perturb the electrophoretic separation. Likewise, to successfully visualize minute amounts of protein present in chromatographic fractions, they must often be concentrated before analysis by SDS-PAGE. In this study, we used a dye precipitation procedure for simultaneous removal of interfering substances and concentration of dilute samples (ng/ml) before analysis by SDS-PAGE. Nanogram amounts of protein (143 ng) were effectively precipitated with a pyrogallol red-molybdate reagent from commonly used chromatographic buffers containing various interfering solutes or solvents. Proteins were successfully precipitated from solution in the presence of organic solvents (acetonitrile, methanol, 2-propanol), chaotropic agents (6 M urea, 6 M guanidine-HCl), a protein stabilizer (40% sucrose), metal chelators (30 mM EDTA and 30 mM EGTA), or high salt (1.0 M NaCl). Detergents, at concentrations up to twice their critical micelle concentrations, from the nonionic class (Triton X-100, Tween 20) or from the zwitterionic class (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate) did not inhibit protein precipitation. Some interference was observed when proteins were precipitated in the presence of ammonium sulfate (0. 5-2.0 M). Proteins did not precipitate in the presence of ionic detergents (SDS and cetyltrimethylammonium bromide). The sensitivity of the combined pyrogallol red-molybdate precipitation/SDS-PAGE procedure is approximately 7 ng. Two other methods of precipitating proteins (trichloroacetic acid and phenol-ether) both exhibited varying degrees of effectiveness, ranging from 714 to 7 ng/ml, in the precipitation of individual proteins. In summary, the pyrogallol red-molybdate protein precipitation procedure facilitates the SDS-PAGE analysis of dilute protein samples (ng/ml) from chromatographic fractions of various compositions. The method is useful for rapid pilot-scale protein fractionation and facilitates the ongoing propensity of researchers to work with minuscule amounts of protein.

Expression and subcellular distribution of filamin isotypes in endothelial cells and pericytes

Two principal forms of the actin binding protein, filamin, are expressed in mammalian cells: nonmuscle and muscle isotypes (FLN-1 and FLN-2). A protein that copurifies with an alpha-naphthyl acetate hydrolyzing esterase from human omentum microvessel endothelial cells (EC) is isolated by nondenaturing electrophoresis, sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis and electroblotting. The purified protein is subjected to in situ trypsin cleavage, reversed-phase high performance liquid chromatography (HPLC) and automated Edman degradation. Six peptide fragments from the protein are identified to have 60-66% identity with nonmuscle filamin (ABP-280). Two of these peptides are 100% identical to a previously sequenced human muscle filamin fragment. Polyclonal antibody is produced using a 16-residue synthetic peptide corresponding to a structural beta-sheet region of muscle filamin. Compared with a variety of vascular cells evaluated, retinal pericytes express an abundance of both muscle and non-muscle filamin isotypes. Pericytes contain at least 10 times more muscle filamin than human umbilical vein EC and at least three times the amount expressed in human omentum microvessel and bovine pulmonary artery EC. Differential detergent fractionation indicates that both filamin isotypes are primarily localized in the cytosol and membrane/organelle fractions of pericytes. Another actin crosslinking protein, alpha-actinin, is primarily found in the cytosol and cytoskeletal fractions. The dynamic regulation of actin microfilament organization in pericytes may be controlled in part by the two filamin isotypes, which in turn may contribute to pericyte contractility.

A luminescent europium complex for the sensitive detection of proteins and nucleic acids immobilized on membrane supports

Certain metal complexes selectively interact with proteins immobilized on solid-phase membrane supports to form brightly colored products. Detecting the absorbance of colorimetric stains is limited by the molar extinction coefficient of the product, however. Development of light-emitting complexes should improve detection sensitivity, but fluorescent labels described to date modify free amino, carboxyl, or sulfhydryl groups often rendering proteins unsuitable for further analysis. Bathophenanthroline disulfonate (BPSA) forms a luminescent europium (Eu) complex that reversibly binds to proteins and nucleic acids. Analysis of charge-fractionated carrier ampholytes and synthetic polymers of different L-amino acids indicates that protein binding is chiefly through protonated alpha- and epsilon-amino side chains. Proteins or nucleic acids immobilized to a nitrocellulose or polyvinyl difluoride membrane by electroblotting, dot-blotting, or vacuum slot-blotting are incubated with the lanthanide complex at acidic pH. Membranes are rinsed, illuminated with UV light and the phosphorescence of BPSA-Eu is measured at 590 to 615 nm using a CCD camera or spectrofluorimeter. The linear dynamic range of the stain is 476- and 48-fold for protein and DNA, respectively. A strong chelating agent such as ethylenediaminetetraacetic acid combined with a shift to basic pH (PH 8-10) elutes BPSA-Eu from the membrane. The reversible nature of the protein staining procedure allows for subsequent biochemical analyses, such as immunoblotting, lectin staining, and mass spectrometry.