Complex formation between Chromatium vinosum ferric cytochrome c' and bromophenol blue

Multicolor Quantum Dot-Based Chemical Nose for Rapid and Array-Free Differentiation of Multiple Proteins

Nanomaterial-based differential sensors (e.g., chemical nose) have shown great potential for identification of multiple proteins because of their modulatable recognition and transduction capability but with the limitation of array separation, single-channel read-out, and long incubation time. Here, we develop a multicolor quantum dot (QD)-based multichannel sensing platform for rapid identification of multiple proteins in an array-free format within 1 min. A protein-binding dye of bromophenol blue (BPB) is explored as an efficient reversible quencher of QDs, and the mixture of BPB with multicolor QDs may generate the quenched QD-BPB complexes. The addition of proteins will disrupt the QD-BPB complexes as a result of the competitive protein-BPB binding, inducing the separation of BPB from the QDs and the generation of distinct fluorescence patterns. The multicolor patterns may be collected at a single-wavelength excitation and differentiated by a linear discriminant analysis (LDA). This multichannel sensing platform allows for the discrimination of ten proteins and seven cell lines with the fastest response rate reported to date, holding great promise for rapid and high-throughput medical diagnostics.

Non-invasive high throughput approach for protein hydrophobicity determination based on surface tension

The surface hydrophobicity of a protein is an important factor for its interactions in solution and thus the outcome of its production process. Yet most of the methods are not able to evaluate the influence of these hydrophobic interactions under natural conditions. In the present work we have established a high resolution stalagmometric method for surface tension determination on a liquid handling station, which can cope with accuracy as well as high throughput requirements. Surface tensions could be derived with a low sample consumption (800 μL) and a high reproducibility (<0.1‰ for water) within a reasonable time (3.5 min per sample). This method was used as a non-invasive HTP compatible approach to determine surface tensions of protein solutions dependent on protein content. The protein influence on the solutions' surface tension was correlated to the hydrophobicity of lysozyme, human lysozyme, BSA, and α-lactalbumin. Differences in proteins' hydrophobic character depending on pH and species could be resolved. Within this work we have developed a pH dependent hydrophobicity ranking, which was found to be in good agreement with literature. For the studied pH range of 3-9 lysozyme from chicken egg white was identified to be the most hydrophilic. α-lactalbumin at pH 3 exhibited the most pronounced hydrophobic character. The stalagmometric method occurred to outclass the widely used spectrophotometric method with bromophenol blue sodium salt as it gave reasonable results without restrictions on pH and protein species.

Electrophoresis of electrostatically assembled fullerene–porphyrin conjugates

The formation of electrostatically coupled assemblies of a series of anionic dendritic fullerene derivatives and cationic porphyrins in buffered aqueous media was studied with gel electrophoresis. Of central interest in these investigations was the variation of the amount of charge carried by the molecules, their size, shape and self-aggregation. Ferric cytochrome c 1 and the more rigid zinc porphyrin served as octacationic species. The two new anionic fullerene derivates 3 and 6 were synthesized. The formation of electrostatic complexes of the fullerene polyelectrolytes 3 and 4 with 1and 2 was clearly evident in the gel electrophoresis experiment. Compounds and showed a similar behaviour towards 2. The electrophoresis experiments confirmed previous results obtained with other techniques on a qualitative level and gave new insights into aggregation phenomena.

Successful recombinant production of Allochromatium vinosum cytochrome c' requires coexpression of cmm genes in heme-rich Escherichia coli JCB712

Cytochrome c' from the purple photosynthetic bacterium Allochromatium vinosum (CCP) displays a unique, reversible dimer-to-monomer transition upon binding of NO, CO, and CN(-). This small, four helix bundle protein represents an attractive model for the study of other heme protein biosensors, provided a recombinant expression system is available. Here we report the development of an efficient expression system for CCP that makes use of a maltose binding protein fusion strategy to enhance periplasmic expression and allow easy purification by affinity chromatography. Coexpression of cytochrome c maturase genes and the use of a heme-rich Escherichia coli strain were found to be necessary to obtain reasonable yields of cytochrome c'. Characterization using circular dichroism, UV-vis spectroscopy, and size-exclusion chromatography confirms the native-like properties of the recombinant protein, including its ligand-induced monomerization.

Detection of Local Polarity of α-Lactalbumin by N-Terminal Specific Labeling with a New Tailor-Made Fluorescent Probe

To detect the local polarity such as the N-terminal domain of a protein molecule, 3-(4-chloro-6-hydrazino-1,3,5-triazinylamino)-7-(dimethylamino)-2-methylphenazine has been designed and synthesized as a polarity-sensitive fluorescent probe by using an s-triazine ring as a backbone, neutral red and hydrazine as a polarity-sensitive fluorophore, and a labeling group, respectively. The fluorescence properties of the probe have been characterized. The probe has the following features: (1) stable in various solvents; (2) the long-wavelength emission of >550 nm that can avoid the interferences of the background fluorescence shorter than 500 nm from common biomacromolecules; and (3) the maximum emission wavelength (lambda(em)) sensitive to solvent polarity only but not to pH and temperature. The hydrazino group in such a probe reacts readily with an active carbonyl produced by transamination of a protein molecule, leading to N-terminal specific attachment of the fluorophore and thereby allowing the monitoring of local polarity. With this probe, the polarity of the N-terminal domain in both native and heat-denatured alpha-lactalbumin has been first determined, which corresponds to that with a dielectric constant of about 16, and the hydrophobic core near the N-terminus is found to be conservative for heating. The present strategy may provide a general method to study the local environmental changes of a protein molecule under different denaturation conditions.

Selective Staining of Proteins with Hydrophobic Surface Sites on a Native Electrophoretic Gel

Chemical proteomics aims to characterize all of the proteins in the proteome with respect to their function, which is associated with their interaction with other molecules. We propose the identification of a subproteomic library of expressed proteins whose native structures are typified by the presence of hydrophobic surface sites, which are often involved in interactions with small molecules, membrane lipids, and other proteins, pertaining to their functions. We demonstrate that soluble globular proteins with hydrophobic surface sites can be detected selectively by staining on an electrophoretic gel run under nondenaturing conditions. The application of these staining techniques may help elucidate new catalytic, transport, and regulatory functionalities in complex proteomic screenings.

The identification of hydrophobic sites on the surface of proteins using absorption difference spectroscopy of bromophenol blue

Hydrophobic sites on the surface of protein molecules are thought to have important functional roles. The identification of such sites can provide information about the function and mode of interaction with other cellular components. While the fluorescence enhancement of polarity-sensitive dyes has been useful in identifying hydrophobic sites on a number of targets, strong intrinsic quenching of Nile red and ANSA dye fluorescence is observed on binding to a cytochrome c('). Fluorescence quenching is also observed to take place in the presence of a variety of other biologically important molecules which can compromise the quantitative determination of binding constants. Absorption difference spectroscopy is shown not to be sensitive to the presence of fluorescence quenchers but sensitive enough to measure binding constants. The dye BPB is shown to bind to the same hydrophobic sites on proteins as polarity-sensitive fluorescence probes. The absorption spectrum of BPB is also observed to be polarity sensitive. A binding constant of 3x10(6)M(-1) for BPB to BSA has been measured by absorption difference spectroscopy. An empirical correlation is observed between the shape of the absorption difference spectrum of BPB and the polarity of the environment. The results indicate that absorption difference spectroscopy of BPB provides a valuable supplement to fluorescence for determining the presence of hydrophobic sites on the surface of proteins as well as a method for measuring binding constants.