Recent advances in the field of artificial hemoproteins: New efficient eco-compatible biocatalysts for nitrene-, oxene- and carbene-transfer reactions

In the last few years, the field of artificial hemoproteins has been expanding through two main strategies involving either the incorporation of synthetic metalloporphyrin derivatives into the chiral cavity of a protein or the directed evolution of natural hemoproteins such as myoglobin and cytochromes P450. First, various synthetic water-soluble porphyrins including ions of transition metals such as iron and manganese have been inserted covalently or by supramolecular anchoring into non-specifically designed native proteins or into proteins modified by a minimum number of mutations. The obtained artificial hemoproteins were able to catalyze oxene transfer reactions such as epoxidation of alkenes or sulfoxidation of sulfides and cyclopropanation reactions with good activities and moderate enantioselectivities. Recently, a second approach, based on the design of the active site of already existing native hemoproteins such as myoglobin and cytochromes P450 by directed evolution, has led to new artificial hemoproteins that are able to catalyze oxene transfer reactions with improved activities as well as with abiological reactions. This approach thus provided promising tools for the catalysis of reactions such as intramolecular or intermolecular carbene and nitrene transfer reactions with high efficiencies. In addition, in all cases, after a few rounds of mutagenesis, mutants that were able to catalyze those reactions with a high enantioselectivity could be obtained. Finally, several groups showed that these new artificial metalloenzymes could also be used for the preparative scale-production of compounds with an excellent enantioselectivity, opening new pathways for the industrial synthesis of compounds of pharmaceutical interest.

Protein bioelectronics: a review of what we do and do not know

We review the status of protein-based molecular electronics. First, we define and discuss fundamental concepts of electron transfer and transport in and across proteins and proposed mechanisms for these processes. We then describe the immobilization of proteins to solid-state surfaces in both nanoscale and macroscopic approaches, and highlight how different methodologies can alter protein electronic properties. Because immobilizing proteins while retaining biological activity is crucial to the successful development of bioelectronic devices, we discuss this process at length. We briefly discuss computational predictions and their connection to experimental results. We then summarize how the biological activity of immobilized proteins is beneficial for bioelectronic devices, and how conductance measurements can shed light on protein properties. Finally, we consider how the research to date could influence the development of future bioelectronic devices.

Various strategies for obtaining oxidative artificial hemoproteins with a catalytic oxidative activity: from "Hemoabzymes" to "Hemozymes"?

The design of artificial hemoproteins that could lead to new biocatalysts for selective oxidation reactions using clean oxidants such as O 2 or H 2 O 2 under ecocompatible conditions constitutes a really promising challenge for a wide range of industrial applications. In vivo, such reactions are performed by heme-thiolate proteins, cytochromes P450, that catalyze the oxidation of drugs by dioxygen in the presence of electrons delivered from NADPH by cytochrome P450 reductase. Several strategies were used to design new artificial hemoproteins to mimic these enzymes, that associate synthetic metalloporphyrin derivatives to a protein that is supposed to induce a selectivity in the catalyzed reaction. A first generation of artificial hemoproteins or "hemoabzymes" was obtained by the non-covalent association of synthetic hemes such as N-methyl-mesoporphyrin IX, Fe(III) -α3β-tetra-o-carboxyphenylporphyrin or microperoxidase 8 with monoclonal antibodies raised against these cofactors. The obtained antibody-metalloporphyrin complexes displayed a peroxidase activity and some of them catalyzed the regio-selective nitration of phenols by H 2 O 2/ NO 2 and the stereo-selective oxidation of sulphides by H 2 O 2. A second generation of artificial hemoproteins or "hemozymes", was obtained by the non-covalent association of non-relevant proteins with metalloporphyrin derivatives. Several strategies were used, the most successful of which, named "host-guest" strategy involved the non-covalent incorporation of metalloporphyrin derivatives into easily affordable proteins. The artificial hemoproteins obtained were found to be able to perform efficiently the stereoselective oxidation of organic compounds such as sulphides and alkenes by H 2 O 2 and KHSO 5.

From “hemoabzymes” to “hemozymes”: towards new biocatalysts for selective oxidations

Two generations of artificial hemoproteins have been obtained: “hemoabzymes”, by non-covalent association of synthetic hemes with monoclonal antibodies raised against these cofactors and “hemozymes”, by non-covalent association of non-relevant proteins with metalloporphyrin derivatives. A review of the different strategies employed as well as their structural and catalytic properties is presented here.

Engineered proteins: redox properties and their applications

Oxidoreductases and metalloproteins, representing more than one third of all known proteins, serve as significant catalysts for numerous biological processes that involve electron transfers such as photosynthesis, respiration, metabolism, and molecular signaling. The functional properties of the oxidoreductases/metalloproteins are determined by the nature of their redox centers. Protein engineering is a powerful approach that is used to incorporate biological and abiological redox cofactors as well as novel enzymes and redox proteins with predictable structures and desirable functions for important biological and chemical applications. The methods of protein engineering, mainly rational design, directed evolution, protein surface modifications, and domain shuffling, have allowed the creation and study of a number of redox proteins. This review presents a selection of engineered redox proteins achieved through these methods, resulting in a manipulation in redox potentials, an increase in electron-transfer efficiency, and an expansion of native proteins by de novo design. Such engineered/modified redox proteins with desired properties have led to a broad spectrum of practical applications, ranging from biosensors, biofuel cells, to pharmaceuticals and hybrid catalysis. Glucose biosensors are one of the most successful products in enzyme electrochemistry, with reconstituted glucose oxidase achieving effective electrical communication with the sensor electrode; direct electron-transfer-type biofuel cells are developed to avoid thermodynamic loss and mediator leakage; and fusion proteins of P450s and redox partners make the biocatalytic generation of drug metabolites possible. In summary, this review includes the properties and applications of the engineered redox proteins as well as their significance and great potential in the exploration of bioelectrochemical sensing devices.

Catalases versus peroxidases: DFT investigation of H₂O₂ oxidation in models systems and implications for heme protein engineering

Catalases and peroxidases are ubiquitous heme enzymes that catalyze the removal of hydrogen peroxide (H(2)O(2)). Both enzymes use one molecule of hydrogen peroxide to form a high valent iron intermediate named Compound I (Cpd I). However, whereas catalase Cpd I oxidizes a second H(2)O(2) molecule to oxygen, peroxidases use this intermediate to oxidize other substrates rather than H(2)O(2). The origin of the different reactivity of peroxidases and catalases is not known, but it is likely to be related to structural differences between the two heme active sites. Recent modeling studies suggest that the oxidation of H(2)O(2) by catalase Cpd I may take place by two hydrogen atom transfer steps. In this work, we investigate how catalases and peroxidases compare along the same hydrogen transfer steps to give hints into the question why peroxidases cannot efficiently oxidize H(2)O(2). The use of simplified models allows us to probe the direct effect of the proximal ligand (tyrosinate in catalases and histidine in peroxidases) without masking from the protein environment. We show that the nature of the fifth ligand (His in peroxidase and Tyr in catalase) has little effect on the energy barriers of the hydrogen transfer steps. On the contrary, the Cpd I-hydrogen peroxide (O(Fe)-O(peroxide)) distance affects significantly the reaction barriers. We propose that the distal side architecture of peroxidases do not allow to attain short O(Cpd I)-O(peroxide) distances, thus resulting in a lower efficiency towards H(2)O(2) oxidation.

Design of functional metalloproteins

Metalloproteins catalyse some of the most complex and important processes in nature, such as photosynthesis and water oxidation. An ultimate test of our knowledge of how metalloproteins work is to design new metalloproteins. Doing so not only can reveal hidden structural features that may be missing from studies of native metalloproteins and their variants, but also can result in new metalloenzymes for biotechnological and pharmaceutical applications. Although it is much more challenging to design metalloproteins than non-metalloproteins, much progress has been made in this area, particularly in functional design, owing to recent advances in areas such as computational and structural biology.