Determination of biotin on a protein by quantitative sodium dodecyl sulfate-capillary gel electrophoresis of monomeric avidin

A G-quadruplex/hemin DNAzyme-based microchip electrophoresis chemiluminescence assay for highly sensitive detection of biotin in flour

Quantitative analysis of biotin in biological fluids, foods, and pharmaceutical is important for diagnosis and treatment of biotin-related diseases and health maintenance. In this work, a novel G-quadruplex/hemin DNAzyme-based microchip electrophoresis chemiluminescence (CL) assay method was established for rapid and highly sensitive detection of biotin. This method is based on the specific binding between biotin and streptavidin, the catalytic CL characteristics of G-quadruplex/hemin DNAzyme to the oxidation-reduction reaction of hydrogen peroxide with luminol, and the on-line separation function of microchip electrophoresis. Under the optimal experimental conditions, on-chip biotin analysis was achieved within 1 min. The CL intensity is linearly proportional to the concentration of biotin in the range of 13-630 nM with a detection limit of 6.4 nM. The proposed method has been applied for the detection of biotin in flour, biotin contents in three flour samples are found in the range of 199-223 ng/g with a mean value of 214 ng/g. The recoveries were in the range of 94-103%. With excellent sensitivity and good selectivity, the proposed method could be applied in a wide range of biological fluids, foods, and pharmaceutical analysis.

Site-specific chemical conjugation of human Fas ligand extracellular domain using trans-cyclooctene - methyltetrazine reactions

Background

Fas ligand plays a key role in the human immune system as a major cell death inducing protein. The extracellular domain of human Fas ligand (hFasLECD) triggers apoptosis of malignant cells, and therefore is expected to have substantial potentials in medical biotechnology. However, the current application of this protein to clinical medicine is hampered by a shortage of the benefits relative to the drawbacks including the side-effects in systemic administration. Effective procedures for the engineering of the protein by attaching useful additional functions are required to overcome the problem.

Results

A procedure for the site-specific chemical conjugation of hFasLECD with a fluorochrome and functional proteins was devised using an inverse-electron-demand Diels-Alder reaction between trans-cyclooctene group and methyltetrazine group. The conjugations in the present study were attained by using much less molar excess amounts of the compounds to be attached as compared with the conventional chemical modification reactions using maleimide derivatives in the previous study. The isolated conjugates of hFasLECD with sulfo-Cy3, avidin and rabbit IgG Fab’ domain presented the functional and the structural integrities of the attached molecules without impairing the specific binding activity toward human Fas receptor extracellular domain.

Conclusions

The present study provided a new fundamental strategy for the production of the engineered hFasLECDs with additional beneficial functions, which will lead to the developments of the improved diagnostic systems and the effective treatment methods of serious diseases by using this protein as a component of novel molecular tools.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-017-0381-2) contains supplementary material, which is available to authorized users.

Quantitation of surface coverage of oligonucleotides bound to chip surfaces: a fluorescence-based approach using alkaline phosphatase digestion

Silanized chip surfaces provide a reliable substrate for immobilization of oligonucleotides. The ability for rapid and sensitive detection of oligonucleotide surface coverage on these chips is crucial for their wide and effective applications in biotechnology. In this paper, two different silanization procedures were used to covalently bind fluorescent-labeled single-stranded DNA onto silicon dioxide or nitride chip surfaces. Effects of surface functionalization techniques for different surfaces, and immobilization conditions, including buffers and solution ionic strength, on surface probe coverage were investigated, quantifying the endpoint probe density by fluorescent measurement upon digestion with alkaline phosphatase (ALP). Digestion of surface-immobilized oligonuleotides with ALP released the fluorophore-tagged probe fragments back into the solution. The detection of DNA was accomplished by laser-induced fluorescence detection of the solution containing those cleaved fragments. The probe surface density on gold thin film, determined by ALP-digestion, was found to coincide well with that measured using the conventional alkanethiol-based fluorescence-displacement technique for the same system. The developed method has important implications for evaluating the performance of different oligonucleotide immobilization strategies. Also, it has the potential to serve as a sample-thrifty, time saving, and therefore routine tool to realize more realistic, practical quantification of the surface coverage of oligonucleotides immobilized on any solid surfaces.

Capturing biotinylated proteins and peptides by avidin functional affinity electrophoresis

Avidin functional affinity electrophoresis (AFAEP) is a variational method of affinity electrophoresis. In this technique, avidin is immobilized within a small area of the gel matrix by interaction with acrylamide and/or polyacrylamide either directly or through bifunctional linker glutaraldehyde during polymerization. Analytes can be heated with Tris-glycine sodium dodecyl sulfate (SDS) sample buffer so that biotinylated peptides/proteins are negatively charged and migrate electrophoretically towards the cathode through the avidin zone regardless of their isoelectric point (pI) values. Alternatively, if the behavior of the biotinylated analytes is known, the SDS treatment is not required. The polarity of the electrodes is set such that biotinylated analytes migrate electrophoretically through the avidin zone. This technique can work with or without SDS in gel running buffer. The AFAEP method allows the capture and concentration of biotinylated peptides/proteins. The values of this technique stem from a combination of merits of polyacrylamide gel electrophoresis and affinity technology.

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.

Biotinylation of heat shock protein 70 induces RANTES production in HEK293 cells in a CD40-independent pathway

Biotinylated proteins and peptides have been used as popular ligands for characterization of cell surface receptors by a variety of methods including flow cytometry. The number and the location of biotin moieties incorporated could alter the structural and physicochemical properties of ligands, although biotin is thought to be such a small molecule (244Da) that it is capable of being conjugated to most proteins without affecting their activity. Here, we demonstrate that the biotinylated HSP70 molecule via primary amines bound to epithelium-like HEK 293 cells in a saturable manner whereas the unlabeled counterparts of HSP70 other than mouse Hsp72 do not. This binding was not competed by either HSP70 or the biotin entity itself. Interestingly, the biotinylated HSP70 also elicited the production of CC-chemokine RANTES independent of CD40 signaling. This response occurred regardless of sequence diversity of HSP70 derived from different species, and neither the biotinylated ovalbumin nor the unlabeled HSP70 cross-linked with a biotinylated protein stimulated a significant level of RANTES production which was induced by biotinylated HSP70 itself. Our findings suggest that modification of HSP70 such as biotinylation may function as a biological alarm signal in the innate immune system.

Transfer in SDS of biotinylated proteins from acrylamide gels to an avidin-coated membrane filter

Avidin was covalently linked to aldehyde-derivatized polyethersulfone membrane filters. These filters were used in Western blot analysis of proteins reacted with biotinylation reagents and electrophoresed in sodium dodecyl sulfate (SDS) on polyacrylamide gels. Electrophoretic transfer from the gels to these filters was in 0.1% SDS, in which the covalently bound avidin retained its biotin-binding capacity. We compared Western blots on avidin-coated membrane filters of biotinylated and nonbiotinylated forms of mouse immunoglobulin G (IgG), mouse IgG heavy chain, muscle-type acetylcholine receptor alpha subunit, and fused alpha and beta subunits of receptor. Biotinylated proteins were captured with high specificity compared to their nonbiotinylated counterparts and sensitively detected on the avidin-coated membranes.

Capturing SDS-treated biotinylated protein and peptide by avidin functional affinity electrophoresis with or without SDS in the gel running buffer

Avidin functional affinity electrophoresis (AFAEP) is a new method of affinity electrophoresis. In this technique, bifunctional linker glutaraldehyde is added to the polyacrylamide gel solution to embed avidin within the gel matrix by interaction with the amino/amide groups. Samples are heated with triglycine sodium dodecyl sulfate (SDS) sample buffer to ensure that biotinylated proteins biotinylated peptides are negatively charged and migrate electrophoretically toward the cathode through the avidin zone regardless of their pI values. The AFAEP method allows the capture and concentration of biotinylated proteins or biotinylated peptides irrespective of the use of SDS in both the sample buffer and the gel running buffer.

Mass spectrometric detection of biotinylated peptides captured by avidin functional affinity electrophoresis

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to detect biotinylated peptides captured by avidin functional affinity electrophoresis (AFAEP). Peptide samples loaded onto AFAEP were heated with sodium dodecyl sulfate to ensure that the peptides are negatively charged, and thus migrate electrophoretically toward the cathode through the embedded avidin zone in the middle of the gel. To detect the biotinylated peptides, the band containing the avidin-biotinylated peptide complexes was excised from a 7.5% w/v native polyacrylamide gel, and biotinylated peptides were extracted with aqueous 95% v/v formamide (pH 8.2), aqueous 6 M guanidine HCl (pH 1.5), or water, at temperatures from 4 to 95 degrees C for periods from 5 min to 24 h. It was observed that all three solvents are capable of extracting biotinylated peptides and avidin from the gel, but the best results were obtained with aqueous 95% v/v formamide (pH 8.2) at 65 degrees C for 20 min. However, some AFAEP-captured biotinylated peptides are not stable and are extensively modified by formamide during extraction at too high a temperature or too long an extraction time.