Functional modulation of cytochrome C upon specific binding to DNA nanoribbons

We discovered that the function of cytochrome C can be modulated by DNA nanoribbons. Meanwhile, the interplay between the DNA nanoribbons and the native cytochrome C and the possible mechanisms are also discussed.

Electron self-exchange of cytochrome c measured via13C detected protonless NMR

The use of protonless 13C′–13C′ EXSY (COCO-EXSY) is proposed here to measure electron self-exchange rates. The experiment is compared to the commonly employed 1H and 15N EXSY experiments using as a reference system human cytochrome c. In COCO-EXSY, the exchange peaks are stronger than in the other experiments with respect to the self peaks and their intensity is less dependent on the choice of the EXSY mixing time. The use of 13C directed detection may be essential for all those cases where T2 relaxation is detrimental, as in the case of proteins containing highly paramagnetic metal centers, or rotating slowly in solution, or where the amide signals are difficult to detect due to chemical or conformational exchange. The proposed experiment has a general applicability and can be used to monitor exchange phenomena different from electron self-exchange.

Dissolution and dissolved state of cytochrome C in a neat, hydrophilic ionic liquid

The dissolution and dissolved molecular state of cytochrome c were investigated in the room temperature ionic liquid ethylmethylimidazolium ethylsulfate, [EMIM][EtSO4], by viscometry, optical and vibrational spectroscopies, and peroxidase activity. In dilute mixtures, viscometry demonstrated true molecular dissolution of cytochrome c in the ionic liquid and uncovered a molecular size larger than that in aqueous buffer, suggesting altered solvation or slight denaturation. The protein's heme unit absorbs light outside the spectral range masked by [EMIM], enabling conformational assessments by UV-visible and circular dichroism spectroscopies. Adding trends from fluorescence and Fourier transform infrared spectroscopy, unchanged secondary but perturbed tertiary structures were determined, consistent with the appreciable peroxidase activity measured. Different than in aqueous buffers, denaturation is not accompanied by aggregation. Results are relevant to the proposed application of ionic liquids as media for room temperature preservation of biomacromolecules.

Head group modulated pH-responsive hydrogel of amino acid-based amphiphiles: entrapment and release of cytochrome c and vitamin B12

The present study describes the rational design and synthesis of amino acid-based amphiphilic hydrogelators, which were systemically fine-tuned at the head group to develop pH-responsive hydrogels. To understand the basic structural requirements of a low molecular weight amphiphilic hydrogelator, 10 analogous amphiphiles based on L-phenylalanine and L-tyrosine with structurally related head group were synthesized. Among them, three with quaternary ammonium substitution at the head group formed transparent hydrogels at room temperature while others were unable to gelate water. To establish correlations between the head group architecture of the gelators and their supramolecular arrangements, a variety of spectroscopic and microscopic techniques were investigated that showed that a balance between hydrophilicity and hydrophobicity is required to achieve hydrogelation. Interestingly, the gelator with tyrosinate in its head group showed remarkable response toward external pH. All hydrogels including the pH-responsive one were used in the controlled and/or pH-triggered release of entrapped (with in hydrogels) vitamin B12 and cytochrome c at different pHs. Since the hydrogels were formed at room temperature without heating, this could be very important during the entrapment of biomolecules such as proteins because of their heat sensitivity. At biological pH (7.4), the release of entrapped biomolecules from all three hydrogels was caused by diffusion through the gel structure, but at endosomal pH (approximately 5.5) and further lower pH, the release rate of biomolecules from the pH-responsive hydrogel with tyrosinate head group (pKa approximately equal to 7.2) increased by 9-10-fold compared to that observed at physiological pH, because of gel dissolution. Retention of the structure and activity of released biomolecule has established the prospect of the hydrogel as an efficient drug delivery vehicle.

Enhancing Stability and Oxidation Activity of Cytochrome c by Immobilization in the Nanochannels of Mesoporous Aluminosilicates

Hydrothermally stable and structrurally ordered mesoporous and microporous aluminosilicates with different pore sizes have been synthesized to immobilize cytochrome c (cyt c): MAS-9 (pore size 90 A), MCM-48-S (27 A), MCM-41-S (25 A), and Y zeolites (7.4 A). The amount of cyt c adsorption could be increased by the introduction of aluminum into the framework of pure silica materials. Among these mesoprous silicas (MPS), MAS-9 showed the highest loading capacity due to its large pore size. However, cyt c immobilized in MAS-9 could undergo facile unfolding during hydrothermal treatments. MCM-41-S and MCM-48-S have the pore sizes that match well the size of cyt c (25 x 25 x 37 A). Hence the adsorbed cyt c in these two medium pore size MPS have the highest hydrothermal stability and overall catalytic activity. On the other hand, the pore size of NaY zeolite is so small that cyt c is mostly adsorbed only on the outer surface and loses its enzymatic activity rapidly. The improved stability and high catalytic activity of cyt c immobilized in MPS are attributed to the electrostatic attraction between the pore surface and cyt c and the confinement provided by nanochannels. We further observed that cyt c immobilized in MPS exists in both high and low spin states, as inferred from the ESR and UV-vis studies. This is different from the native cyt c, which shows primarily the low spin state. The high spin state arises from the replacement of Met-80 ligands of heme Fe (III) by water or silanol group on silica surface, which could open up the heme groove for easy access of oxidants and substrates to iron center and facilitate the catalytic activity. In the catalytic study, MAS-9-cyt c showed the highest specific activity toward the oxidation of polycyclic aromatic hydrocarbons (PAHs), which arises from the fast mass transfer rate of reaction substrate due to its large pore size. For pinacyanol (a hydrophilic substrate), MCM-41-S-cyt c and MCM-48-S-cyt c showed higher specific activity than NaY-cyt c and MAS-9-cyt c. The result indicated that cyt c embedded in the channels of MCM-41-S and MCM-48-S was protected against unfolding and loss of activity. By increasing the concentration of the spin trapping agent, 5,5-dimethyl-1-pyrroline N-oxide (DMPO) in ESR experiments, we showed that cyt c catalyzes a homolytic cleavage of the O-O bond of hydroperoxide and generates a protein cation radical (g = 2.00). Possible mechanisms for MPS-cyt c catalytic oxidation of hydroperoxides and PAHs are proposed based on the spectroscopic characterizations of the systems.

Third-generation biosensors based on the direct electron transfer of proteins

Recent progress in third-generation electrochemical biosensors based on the direct electron transfer of proteins is reviewed. The development of three generations of electrochemical biosensors is also simply addressed. Special attention is paid to protein-film voltammetry, which is a powerful way to obtain the direct electron transfer of proteins. Research activities on various kinds of biosensors are discussed according to the proteins (enzymes) used in the specific work.

Enhanced Peroxidase Activity of Hemoglobin in a DNA Membrane and Its Application to an Unmediated Hydrogen Peroxide Biosensor

Hemoglobin can exhibit not only a direct electron transfer reacting after being entrapped in a DNA membrane, but also a greatly enhanced peroxidase activity toward the reduction of hydrogen peroxide. Based on the direct electrochemical property and nice enzymatic activity of the protein in a DNA membrane, a reagentless hydrogen peroxide biosensor was prepared. The peak current related to hydrogen peroxide was linearly proportional to its concentration in the range of 1.9 x 10(-6)-6.8 x 10(-4) mol L(-1). The detection limit was 1 x 10(-6) mol/L.

High temperature peroxidase activities of HRP and hemoglobin in the galleries of layered Zr(IV)phosphate

Horseradish peroxidase, and met hemoglobin, when intercalated in the galleries of alpha-Zr(IV) phosphate, show peroxidase activities at elevated temperatures (86-90 degrees C) and the rates increased to 2-3.6 times the rates observed at room temperature.

Complex formation of cytochrome C with a calixarene carboxylic acid derivative: a novel solubilization method for biomolecules in organic media

A calixarene carboxylic acid derivative has been found to form a complex with the cationic protein cytochrome c. The solubilized cytochrome c was stable and showed peroxidase activity in chloroform. The calix[6]arene and the calix[8]arene achieved quantitative extraction of the protein. The calix[6]arene, whose cavity is well-fitted to a protonated amino group, exhibited a selectivity to lysine-rich proteins due to the recognition of the epsilon-amino groups in lysine residues on the surface of the protein. This is the first report showing protein extraction by calixarenes. The solubilized cytochrome c could catalyze an oxidative reaction in organic solvents. This host compound functions as a novel solubilization tool for biomolecules and a separation tool for lysine-rich proteins.

Influence of cluster formation of acidic phospholipids on decrease in the affinity for ATP of DnaA protein

DnaA protein is the initiator of chromosomal DNA replication in Escherichia coli. We examined the influence of artificial mixed membrane composed of synthetic acidic (phosphate) lipid and basic (ammonium) lipid on the affinity of DnaA protein for ATP. Two sets of acidic and basic lipids with distinguishable numbers of hydrophobic alkyl chains were devised. Synthetic membranes made of the sole acidic lipid but not the basic bilayers inhibited the ATP binding to DnaA protein and stimulated the release of ATP from the ATP-DnaA complex. The basic bilayer-forming compounds served as the matrix for the guest acidic lipids. Acidic lipids dispersed in the basic matrix membrane had little effect on ATP binding and on ATP release. Conversely, acidic lipids forming cluster structures in the mixed artificial membranes inhibited the ATP binding and stimulated the release of ATP. These observations suggest that in mixed lipid bilayers, a cluster structure of acidic lipids seems to be an important parameter to decrease the affinity of DnaA protein for ATP.