Design and fine-tuning redox potentials of metalloproteins involved in electron transfer in bioenergetics

Abstract

Redox potentials are the major contributors to controlling the ET rates and thus regulating ET processes in the bioenergetics. To maximize the efficiency of the ET process, one needs to master the art of tuning of the E°, especially metalloproteins, as they represent major classes of ET proteins. In this review, we first describe the importance of tuning E° of ET centers, including the metalloproteins described above, and its role in regulating the ET in bioenergetic processes including photosynthesis and respiration. The major focus of this review is to summarize recent work in designing the ET centers, namely cupredoxins, cytochromes, and iron-sulfur proteins, and examples in design of protein networks involved these ET centers. We then discuss the factors that affect redox potentials of these ET centers including metal ion, the ligands to metal center and interactions beyond the primary ligand, especially non-covalent secondary coordination sphere interactions. We gave examples of strategies to fine-tune the redox potential using both natural and unnatural amino acids and native and nonnative cofactors. Several case studies are used to illustrate recent successes in this area. Outlooks for future endeavors are also provided.

Properties of Site-Specifically Incorporated 3-Aminotyrosine in Proteins To Study Redox-Active Tyrosines: Escherichia coli Ribonucleotide Reductase as a Paradigm

“…12, 13 Protein environments can alter reduction potentials substantially. 5 A rationalization of NH 2 Y-RNRs activities, therefore, could be based on our previous spectroscopic analysis of NH 2 Y 730 • and the ambiguity associated with the NH 2 • conformation 59, 60 based on methods available at the time. 25–27 We thus undertook DFT calculations and developed a new method to directly determine the hfcs associated with the two NH 2 • protons, a key indicator of geometric distortion.…”

The Role of Microbial Electron Transfer in the Coevolution of the Biosphere and Geosphere

“…An electron transfer pathway is most efficient with cofactors in the pathway ordered by redox potential (24), with centers approximately 14 Å apart (100)-both highly conserved structural features of EC1 enzymes. Cofactors generally coordinate with specific ligands, allowing a finetuning of their native redox potentials (57). The redox tuning is strongly related to the protein environment (23) and is generally accomplished by one of three broad mechanisms.…”

Design of Heteronuclear Metalloenzymes

“…Heme proteins in particular exhibit strong UV-Vis spectroscopic signals characteristic to their oxidized and reduced states that are useful to deduce their heme E∘′. Protocols for measurement of heme E∘′ for Fe 3+/2+ couple through spectroelectrochemistry are fairly standardized and discussed extensively in other reviews(Taboy et al, 1999, Hosseinzadeh & Lu, 2015). Cyclic voltammetry (CV) can also be used to measure E∘′ of a heterobinuclear center.…”

“…The secondary interactions can confer their roles in many ways: engaging in a hydrogen bond or salt bridge to the primary ligands, changing the overall electrostatic environment of the metal binding site by changing charge or hydrophobicity, engaging in proton or electron transfer, or providing space for the metal cofactors (Hosseinzadeh & Lu, 2015). The stability and reactivity of heteronuclear metal-binding sites depends heavily on secondary sphere interactions that may contribute to electronic coupling between metal cofactors, the redox potential (E∘′) of one or both metals, and the stabilization of substrates and reactive intermediates (Yikilmaz et al, 2002, Jackson & Brunold, 2004, Marshall et al, 2009, Berry et al, 2010, Shook & Borovik, 2010, New et al, 2012, Petrik et al, 2016).…”