An improved, luminescent europium-based stain for detection of electroblotted proteins on nitrocellulose or polyvinylidene difluoride membranes

Positively charged polymer brush-functionalized filter paper for DNA sequence determination following Dot blot hybridization employing a pyrrolidinyl peptide nucleic acid probe

As inspired by the Dot blot analysis, a well known technique in molecular biology and genetics for detecting biomolecules, a new paper-based platform for colorimetric detection of specific DNA sequences employing peptide nucleic acid (PNA) as a probe has been developed. In this particular study, a pyrrolidinyl PNA bearing a conformationally rigid d-prolyl-2-aminocyclopentanecarboxylic acid backbone (acpcPNA) was used as a probe. The filter paper was modified to be positively charged with grafted polymer brushes of quaternized poly(dimethylamino)ethyl methacrylate (QPDMAEMA) prepared by surface-initiated polymerization of 2-(dimethylamino)ethyl methacrylate from the filter paper via ARGET ATRP followed by quaternization with methyl iodide. Following the Dot blot format, a DNA target was first immobilized via electrostatic interactions between the positive charges of the QPDMAEMA brushes and negative charges of the phosphate backbone of DNA. Upon hybridization with the biotinylated pyrrolidinyl peptide nucleic acid (b-PNA) probe, the immobilized DNA can be detected by naked eye observation of the yellow product generated by the enzymatic reaction employing HRP-labeled streptavidin. It has been demonstrated that this newly developed assay was capable of discriminating between complementary and single base mismatch targets at a detection limit of at least 10 fmol. In addition, the QPDMAEMA-grafted filter paper exhibited a superior performance to the commercial membranes, namely Nylon 66 and nitrocellulose.

Lanthanide-based time-resolved luminescence immunoassays

The sensitive and specific detection of analytes such as proteins in biological samples is critical for a variety of applications, for example disease diagnosis. In immunoassays a signal in response to the concentration of analyte present is generated by use of antibodies labeled with radioisotopes, luminophores, or enzymes. All immunoassays suffer to some extent from the problem of the background signal observed in the absence of analyte, which limits the sensitivity and dynamic range that can be achieved. This is especially the case for homogeneous immunoassays and surface measurements on tissue sections and membranes, which typically have a high background because of sample autofluorescence. One way of minimizing background in immunoassays involves the use of lanthanide chelate labels. Luminescent lanthanide complexes have exceedingly long-lived luminescence in comparison with conventional fluorophores, enabling the short-lived background interferences to be removed via time-gated acquisition and delivering greater assay sensitivity and a broader dynamic range. This review highlights the potential of using lanthanide luminescence to design sensitive and specific immunoassays. Techniques for labeling biomolecules with lanthanide chelate tags are discussed, with aspects of chelate design. Microtitre plate-based heterogeneous and homogeneous assays are reviewed and compared in terms of sensitivity, dynamic range, and convenience. The great potential of surface-based time-resolved imaging techniques for biomolecules on gels, membranes, and tissue sections using lanthanide tracers in proteomics applications is also emphasized.

Heterologous hyper-expression of a glucansucrase-type glycosyltransferase gene

Heterologous expression of the large glucansucrase-type glycosyltransferases genes is still a challenge, and typically yields are poor. Therefore, a number of different Escherichia coli systems for the expression of such a gene, encoding the glycosyltransferase R (GtfR) from Streptococcus oralis, were constructed and evaluated. We thereby obtained a strain producing the highest molar yields described so far for this class of enzymes. Cloning of a 5'-terminally truncated version of the gene in the expression vector pET33b(+) yielded, in dissolved form, about 2 micromol (300 mg) of enzyme per liter of culture of an optical density at 600 nm of four. Problems frequently encountered in the heterologous biosynthesis of this class of enzymes, such as formation of a high fraction of insoluble aggregates and/or proteolytic degradation, were not observed in the described system. The over-produced enzyme, devoid of almost its entire variable region, retained its characteristic activities.

Europium tetracycline as a luminescent probe for nucleoside phosphates and its application to the determination of kinase activity

The determination of enzyme activities and the screening of enzyme regulators is a major task in clinical chemistry and drug development. A broad variety of enzymatic reactions is associated with the consumption of adenosine triphosphate (ATP), including, in particular, phosphorylation reactions catalyzed by kinases, formation of adenosine cyclic monophosphate (cAMP) by adenylate cyclases, and ATP decomposition by ATPase. We have studied the effect of a series of adenosine (ATP, ADP, AMP, cAMP) and guanosine (GTP, GDP) phosphoric esters, and of pyrophosphate (PP) on the fluorescence emission of the europium tetracycline (EuTC) complex. We found that these compounds have strongly different quenching effects on the luminescence emission of EuTC. The triphosphates ATP and GTP behave as strong quenchers in reducing the fluorescence intensity of EuTC to 25 % of its initial value by formation of a ternary 1:1:1 complex. All other phosphate esters showed a weak quenching effect only. The applicability of this fluorescent probe to the determination of the activity of phosphorylation enzymes is demonstrated by means of creatine kinase as a model for non-membrane-bound kinases. In contrast to other methods, this approach does not require the use of radioactively labeled ATP substrates, additional enzymes, or of rather complex immunoassays.

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.

Determination of proteins with fullerol by a resonance light scattering technique

Fullerol has been synthesized through the reaction of fullerene C60 with NaOH in aqueous solution by means of ultrasonic agitation and characterized by infrared and 1H-nuclear magnetic resonance spectroscopy. The fullerol obtained shows good solubility and excellent stability in water. A weak resonance light scattering (RLS) spectrum of fullerol was observed in aqueous solution. However, the intensity of the RLS signal could be enhanced in the presence of proteins, including bovine serum albumin (BSA), human serum albumin (HSA), pepsin (Pep), and lysozyme (Lys). Based on the enhancement of the RLS, a sensitive method for the determination of proteins has been established. The quantitative conditions were considered with regard to the effects of the pH, the ion strength, and the concentration of the fullerol. Under the optimum conditions, the intensity of the RLS was proportional to the concentration of proteins with the limits of detection of 9.7, 10.9, 57.4, and 8.5 ng mL(-1) for BSA, HSA, Pep, and Lys, respectively. Almost no interference can be observed from some amino acids, nucleic acids, and most of the metal ions. The model samples and human serum samples were determined satisfactorily with the proposed method.

A high-affinity reversible protein stain for Western blots

We describe a reversible staining technique, using MemCode, a reversible protein stain by which proteins can be visualized on nitrocellulose and polyvinylidine fluoride (PVDF) membranes without being permanently fixed to the membrane itself. This allows subsequent immunoblot analysis of the proteins to be performed. The procedure is applicable only to protein blots on nitrocellulose and PVDF membranes. MemCode is a reversible protein stain composed of copper as a part of an organic complex that interacts noncovalently with proteins. MemCode shows rapid protein staining, taking 30s to 1 min for completion. The method is simple and utilizes convenient application conditions that are compatible with the matrix materials and the protein. The stain is more sensitive than any previously described dye-based universal protein staining system. The turquoise-blue-stained protein bands do not fade with time and are easy to photograph compared to those stained with Ponceau S. Absorbance in the blue region of the spectrum offers good properties for photo documentation and avoids interference from common biological chromophores. The stain on the protein is easily reversible in 2 min for nitrocellulose membrane and in 10 min for PVDF membrane with MemCode stain eraser. The stain is compatible with general Western blot detection systems, and membrane treatment with MemCode stain does not interfere with conventional chemiluminescent or chromogenic detection using horseradish peroxide and alkaline phosphatase substrates. The stain is also compatible with N-terminal sequence analysis of proteins.

An improved formulation of SYPRO Ruby protein gel stain: comparison with the original formulation and with a ruthenium II tris (bathophenanthroline disulfonate) formulation

SYPRO Ruby protein gel stain is compatible with a variety of imaging platforms since it absorbs maximally in the ultraviolet (280 nm) and visible (470 nm) regions of the spectrum. Dye localization is achieved by noncovalent, electrostatic and hydrophobic binding to proteins, with signal being detected at 610 nm. Since proteins are not covalently modified by the dye, compatibility with downstream proteomics techniques such as matrix-assisted laser desorption/ionisation-time of flight mass spectrometry is assured. The principal limitation of the original formulation of SYPRO Ruby protein gel stain, is that it was only compatible with a limited number of gel fixation procedures. Too aggressive a fixation protocol led to diminished signal intensity and poor detection sensitivity. This is particularly apparent when post-staining gels subjected to labeling with other fluorophores such as Schiff's base staining of glycoproteins with fluorescent hydrazides. Consequently, we have developed an improved formulation of SYPRO Ruby protein gel stain that is fully compatible with commonly implemented protein fixation procedures and is suitable for post-staining gels after detection of glycoproteins using the green fluorescent Pro-Q Emerald 300 glycoprotein stain or detection of beta-glucuronidase using the green fluorescent ELF 97 beta-D-glucuronide. The new stain formulation is brighter, making it easier to manually excise spots for peptide mass profiling. An additional benefit of the improved formulation is that it permits staining of proteins in isoelectric focusing gels, without the requirement for caustic acids.

Simultaneous red/green dual fluorescence detection on electroblots using BODIPY TR-X succinimidyl ester and ELF 39 phosphate

A two-color fluorescence detection method is described based upon covalently coupling the succinimidyl ester of BODIPY TR-X dye to proteins immobilized on polyvinylidene difluoride membranes, followed by detection of target proteins using the fluorogenic, precipitating substrate ELF 39-phosphate in combination with alkaline phosphatase conjugated reporter molecules. This results in all proteins in the profile being visualized as fluorescent red signal while those detected specifically with the alkaline phosphatase conjugate appear as fluorescent green signal. The dichromatic detection system is broadly compatible with ultraviolet epi- or trans-illuminators combined with photographic or charge-coupled device cameras, and xenon-arc sources equipped with appropriate excitation/emission filters. The dichromatic method permits detection of low nanogram amounts of protein and allows for unambiguous identification of target proteins relative to the entire protein profile on a single electroblot, obviating the need to run replicate gels that would otherwise require visualization of total proteins by silver staining and subsequent alignment with chemiluminescent or colorimetric signals generated on electroblots. Combining the detection approach with an Alexa Fluor 350 dye conjugated monoclonal antibody permits simultaneous fluorescence detection of two antigens and the total protein profile on the same electroblot.