Electrostatic Effects on the Thermodynamics of Protonation of Reduced Plastocyanin

Battistuzzi, Gianantonio; Borsari, Marco; Rocco, Giulia Di; Leonardi, Alan; Ranieri, Antonio; Sola, Marcó

doi:10.1002/cbic.200400310

Cited by 11 publications

(22 citation statements)

References 38 publications

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“…The entropy gain upon reduction is indeed typical of heme centers exposed to solvent, due to the reduction-induced decrease of solvent ordering following the charge change of the heme center from +1 to 0. 79,[81][82][83] The E o0 value is almost invariant up to 5 M urea (Table 1, Fig. 3A), once again as a result of a solvation-related compensatory change (decrease) of the reduction thermodynamics, which in this case is almost perfect, indicating that the changes in reduction thermodynamics upon increasing urea concentration are dominated by changes in solvent reorganization effects, as expected for an increasingly unfolded structure with the heme center more exposed to solvent.…”

Section: Discussionmentioning

confidence: 65%

“…Reduction-induced solvent reorganization effects are known to be perfectly compensative. 82,83 Therefore, the resulting decrease in E o0 is likely to be due to an enthalpic effect related to the increased polarity of the heme environment. This is consistent with the increased exposure of the heme center to solvent due to the urea-induced breaking of the H-bonding network that stabilizes the 'yellow' O foldon responsible for the hydrophobicity of the heme crevice, 84 as shown previously for wt cytc.…”

Section: Discussionmentioning

confidence: 99%

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Effect of motional restriction on the unfolding properties of a cytochrome c featuring a His/Met–His/His ligation switch

et al. 2014

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The K72A/K73H/K79A variant of cytochrome c undergoes a reversible change from a His/Met to a His/His axial heme ligation upon urea-induced unfolding slightly below neutral pH. The unfolded form displays a dramatically lower reduction potential than the folded species along with a pseudo-peroxidase activity. We have studied electrochemically the effects of urea-induced unfolding on the protein electrostatically immobilized on an electrode surface functionalized by means of a negatively charged molecular spacer. The latter mimics the electrostatic interaction with the inner mitochondrial membrane. This behavior has been compared with the unfolding of the same species in solution. This system constitutes a model to decipher the role of the above electrostatic interaction in the unfolding of cytochrome c at physiological pH upon interaction with the membrane component phospholipid cardiolipin in the early stages of the apoptosis cascade. We found that immobilization obstacles protein unfolding due to structural constraints at the interface imposed by protein-SAM interaction.

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Section: Discussionmentioning

confidence: 65%

Section: Discussionmentioning

confidence: 99%

Effect of motional restriction on the unfolding properties of a cytochrome c featuring a His/Met–His/His ligation switch

et al. 2014

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“…The values of both ΔHº ' and ΔS º' in aqueous solution compare well with previous reports on immobilised cyt c. 22 The enthalpic effect is thought to be mainly related to the stabilisation of the Fe 3+ state by ligand binding 25 interactions (in particular the thioether sulfur ligation of the axial methionine), to the hydrophobic environment of the haem, and to the accessibility of the haem to the solvent. From the observed increase in ΔHº ' , the Fe 3+ form of cytochrome c is preferentially stabilised in methanol, a 30 stabilisation that may reflect the displacement of methionine as a ligand. Entropy changes play an important role in the modulation of the reduction potential of haem proteins.…”

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confidence: 96%

“…Entropy changes play an important role in the modulation of the reduction potential of haem proteins. 28,29 The values of DS1 0 are related to protein structural changes (protein flexibility); alteration of solvent dielectric about the metal centre and the influence of ligation. Solvent reorganisation effects also play a major role in determining DS1 0 values.…”

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confidence: 99%

“…Solvent reorganisation effects also play a major role in determining DS1 0 values. 28,29 Ferrocytochrome c is more compact in structure than ferricytochrome c. 30 The entropic data suggest that the degree of conformational flexibility of the reduced protein is increased relative to that of the oxidised protein and may be indicative of partial denaturation of the protein.…”

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Reversible increase in the redox potential of cytochrome c in methanol

Crilly

Magner

2009

Chem. Commun.

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The E o' of cytochrome c on a self-assembled monolayer (SAM) modified gold electrode increased by 300 mV immediately on immersion in methanol. On re-immersion of the electrode in aqueous buffer the original faradaic response was restored, but over a period of 120 min, indicating that methanol causes a 10 significant change in conformation/orientation of the protein.Much effort has been devoted to understanding the electrochemical properties of redox proteins and enzymes. 1 For applications such as biosensors and biofuel cells, 2 it is desirable to have direct and fast electron transfer kinetics 15 between the electrode and the biological component of interest. 3 However, the rate of direct electron transfer (DET) may be inherently slow due to a range of factors including: inaccessibility of the electroactive group in the protein structure; adsorption of the protein in a manner which does 20 not promote fast electron transfer or denaturation of the protein. 4,5 Modified electrodes can enhance the rate of electron transfer, and provide the opportunity to conduct detailed thermodynamic and kinetic studies. 6,7 The use of selfassembled monolayers on electrodes to promote electron 25 transfer between the redox protein of interest and the electrode has been widely used. [7][8][9][10][11] Factors that influence the E o' of haem proteins include the nature of the axial ligands; the polarity of the haem environment and the extent of haem surface exposure. 12-15 30 Despite numerous studies, the full range and effects of the factors that contribute to E o' and their relative contribution has not yet been determined. While the majority of enzyme use occurs in aqueous media e.g. glucose analysis 16 , enzymes can also catalyse reactions in nonaqueous media 17 and can be used 35 in synthetic reactions. 18 However, there have been relatively few studies of the electrochemical properties of enzymes in organic media. Cyt c is one of the most extensively studied redox proteins 19 and has been widely used as a model for larger, more complex systems. 20 The reduction of the 40 immobilised haem fragment of cytochrome c, microperoxidase-11, has been examined in aqueous buffer and glycerol. The increase of 30 mV in E o' in glycerol was dominated by entropic changes. 21 Immobilised cytochrome c showed a smaller increase (7 mV) in E o' on immersion in 45 glycerol, however the change was dominated by enthalpic changes. 22 Faradaic responses were observed for MP-11 in acetonitrile and ethanol, with increases of 60 and 64 mV in E o' , respectively. 23 The reduction of cyt c in solution was examined in a range of mixed solvents, with reversible 50 responses (E o' ranging from 199 -274 mV vs SHE) obtained in methanol, acetonitrile, DMF and DMSO. 24-25 Here we describe the direct electrochemical response of cyt c in methanol at a SAM modified gold electrode. The E o' increased immediately on immersion in methanol, returning to the 55 original value in aqueous solution, but on a much longer time scale, indicating that methanol causes a si...

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Prediction of Reduction Potentials of Copper Proteins with Continuum Electrostatics and Density Functional Theory

Fowler

Blanford

Warwicker

et al. 2017

Chemistry A European J

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Blue copper proteins, such as azurin, show dramatic changes in Cu2+/Cu+ reduction potential upon mutation over the full physiological range. Hence, they have important functions in electron transfer and oxidation chemistry and have applications in industrial biotechnology. The details of what determines these reduction potential changes upon mutation are still unclear. Moreover, it has been difficult to model and predict the reduction potential of azurin mutants and currently no unique procedure or workflow pattern exists. Furthermore, high‐level computational methods can be accurate but are too time consuming for practical use. In this work, a novel approach for calculating reduction potentials of azurin mutants is shown, based on a combination of continuum electrostatics, density functional theory and empirical hydrophobicity factors. Our method accurately reproduces experimental reduction potential changes of 30 mutants with respect to wildtype within experimental error and highlights the factors contributing to the reduction potential change. Finally, reduction potentials are predicted for a series of 124 new mutants that have not yet been investigated experimentally. Several mutants are identified that are located well over 10 Å from the copper center that change the reduction potential by more than 85 mV. The work shows that secondary coordination sphere mutations mostly lead to long‐range electrostatic changes and hence can be modeled accurately with continuum electrostatics.

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Electrostatic Effects on the Thermodynamics of Protonation of Reduced Plastocyanin

Cited by 11 publications

References 38 publications

Effect of motional restriction on the unfolding properties of a cytochrome c featuring a His/Met–His/His ligation switch

Effect of motional restriction on the unfolding properties of a cytochrome c featuring a His/Met–His/His ligation switch

Reversible increase in the redox potential of cytochrome c in methanol

Prediction of Reduction Potentials of Copper Proteins with Continuum Electrostatics and Density Functional Theory

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