Electron Transfer Processes In Proteins Research Articles

The Active Site Loop Modulates the Reorganization Energy of Blue Copper Proteins by Controlling the Dynamic Interplay with Solvent.

Understanding the factors governing the rate of electron transfer processes in proteins is crucial not only to a deeper understanding of redox processes in living organisms but also for the design of efficient devices featuring biological molecules. Here, molecular dynamics simulations performed on native azurin and four chimeric cupredoxins allow for the calculation of the reorganization energy and of structure-related quantities that were used to clarify the molecular determinants to the dynamics/function relationship in blue copper proteins. We find that the dynamics of the small, metal-binding loop region controls the outer-sphere reorganization energy not only by determining the exposure of the active site to solvent but also through the modulation of the redox-dependent rearrangement of the whole protein scaffold and of the surrounding water molecules.

Harry Gray Wins Wolf Prize In Chemistry

The 2004 Wolf Foundation Prize in chemistry has been awarded to Harry B. Gray, the Arnold 0. Beckman Professor of Chemistry and founding director of the Beckman Institute at California Institute of Technology. Gray is being recognized for pioneering work in bioinorganic chemistry—specifically, for contributions to unraveling novel principles of structure and long-range electron-transfer processes in proteins. Among other accomplishments, Gray is credited with using specially modified proteins to measure the rate of electron transfer between redox centers positioned at fixed distances from one another in the proteins. He and his coworkers demonstrated that electron transfer can occur at significant rates even between centers separated by some 20 Â. Electron-transfer reactions in proteins provide the basis for energy production in cells of all living organisms. Yet until Gray's work, little was known about the chemical factors that govern electron transfer in biological systems, the award panel notes. It...

Self-tunnelling oscillations in non-linear quantum mechanics and the electron-transfer problem

A small quantum system with a non-linear self-consistent potential may display a spontaneous symmetry breaking of the ground state. This simple result, which can be interpreted also as a spontaneous self-localization of the wavefunction, results in the presence of several equivalent ground states, which do not exist simultaneously. There is a virtual degeneracy in the system. The addition of a stochastic perturbation (noise) to such a system provides the possibility of tunnelling among the different equivalent ground states. The tunnelling process can lock itself in into a characteristic frequency related to the dynamics of the system and not contained in the input noise. A self-pulsating quantum system is then generated based on the intrinsic non-linearity of the dynamics and the presence of noise, which is used as a seed. We inquiry into the relevance of these phenomena for electron transfer processes in large biomolecules. By combining non-linearity and noise a controlled transfer rate can be achieved in what is effectively a quantum-switch regulated by external perturbations; a mechanism that could be at work in many electron-transfer processes in proteins.

Synthesis of an amino-functionalized model of the Fe-only hydrogenase active site.

A dinuclear 2Fe2S mimic 6 of the active site of the Fe-only hydrogenases has been synthesized. Complex 6 contains a free amino group which enables linkage to a protein backbone or to a redox active species for the study of electron transfer processes in proteins or in supramolecular systems. The structures of the complex 6 and its Boc-protected precursor 5 could be verified by X-ray crystallography.

The role of the medium in long-range electron transfer

The role of the polypeptide matrix in electron transfer processes in proteins has been studied in two distinct systems: first in a protein where the induced ET is artificial, and second as part of the catalytic cycle of an enzyme. Azurins are structurally well-characterized blue single-copper proteins consisting of a rigid β-sheet polypeptide matrix. We have determined rate constants and activation parameters for intramolecular long-range electron transfer between the disulfide radical anions (generated by pulse radiolysis) and the copper(II) centre as a function of driving force and nature of the intervening medium in a large number of wild-type and single-site-mutated proteins. In ascorbate oxidase, for which the three-dimensional structure is equally well characterized, the internal ET from the type-I Cu(I) to the trinuclear Cu(II) centre has been studied. We find that the results correlate well with distance through well-defined pathways using a through-bond electron tunnelling mechanism.

Synthesis of a beta-turn forming depsipeptide for hydrogen bond mediated electron transfer studies

Hydrogen bonds are believed to play an important role in the mediation of electron transfer processes in proteins. A porphyrin/depsipeptide/ p-benzoquinone molecule has been synthesized to help understand this role of hydrogen bond mediated electron transfer in proteins. The synthesis, room temperature folding conformation, and steady-state electron transfer are described.