Sustainable Approach for Peroxygenase-Catalyzed Oxidation Reactions Using Hydrogen Peroxide Generated from Spent Coffee Grounds and Tea Leaf Residues

Peroxygenases are promising catalysts for use in the oxidation of chemicals as they catalyze the direct oxidation of a variety of compounds under ambient conditions using hydrogen peroxide (H₂O₂) as an oxidant. Although the use of peroxygenases provides a simple method for oxidation of chemicals, the anthraquinone process currently used to produce H₂O₂ requires significant energy input and generates considerable waste, which negatively affects process sustainability and production costs. Thus, generating H₂O₂ for peroxygenases on site using an environmentally benign method would be advantageous. Here, we utilized spent coffee grounds (SCGs) and tea leaf residues (TLRs) for the production of H₂O₂. These waste biomass products reacted with molecular oxygen and effectively generated H₂O₂ in sodium phosphate buffer. The resulting H₂O₂ was utilized by the bacterial P450 peroxygenase, CYP152A1. Both SCG-derived and TLR-derived H₂O₂ promoted the CYP152A1-catalyzed oxidation of 4-methoxy-1-naphthol to Russig's blue as a model reaction. In addition, when CYP152A1 was incubated with styrene, the SCG and TLR solutions enabled the synthesis of styrene oxide and phenylacetaldehyde. This new approach using waste biomass provides a simple, cost-effective, and sustainable oxidation method that should be readily applicable to other peroxygenases for the synthesis of a variety of valuable chemicals.

Light-driven catalysis with engineered enzymes and biomimetic systems

Efforts to drive catalytic reactions with light, inspired by natural processes like photosynthesis, have a long history and have seen significant recent growth. Successfully engineering systems using biomolecular and bioinspired catalysts to carry out light-driven chemical reactions capitalizes on advantages offered from the fields of biocatalysis and photocatalysis. In particular, driving reactions under mild conditions and in water, in which enzymes are operative, using sunlight as a renewable energy source yield environmentally friendly systems. Furthermore, using enzymes and bioinspired systems can take advantage of the high efficiency and specificity of biocatalysts. There are many challenges to overcome to fully capitalize on the potential of light-driven biocatalysis. In this mini-review, we discuss examples of enzymes and engineered biomolecular catalysts that are activated via electron transfer from a photosensitizer in a photocatalytic system. We place an emphasis on selected forefront chemical reactions of high interest, including CH oxidation, proton reduction, water oxidation, CO₂ reduction, and N₂ reduction.

Antibody-Directed Synthesis of Catalytic Nanoclusters for Bioanalytical Assays

Synthesis of atomic nanoclusters (NCs) using proteins as a scaffold has attracted great attention. Usually, the synthetic conditions for the synthesis of NCs stabilized with proteins require extreme pH values or temperature. These harsh reaction conditions cause the denaturation of the proteins and end up in the loss of their biological functions. Until now, there are no examples of the use of antibodies as NC stabilizers. In this work, we present the first method for the synthesis of catalytic NCs that uses antibodies for the stabilization of NCs. Anti-BSA IgG was used as a model to demonstrate that it is possible to use an antibody as a scaffold for the synthesis of semiconductor and metallic NCs with catalytic properties. The synthesis of antibodies modified with NCs is carried out under nondenaturing conditions, which do not affect the antibody structure. The resulting antibodies still maintain the affinity for target antigens and protein G. The catalytic properties of the anti-BSA IgG modified with NCs can be used to the quantification of bovine serum albumin (BSA) in a direct sandwich enzyme-linked immunosorbent assay (ELISA).

Keeping the spotlight on cytochrome P450

This review describes the recent advances utilizing photosensitizers and visible light to harness the synthetic potential of P450 enzymes. The structures of the photosensitizers investigated to date are first presented along with their photophysical and redox properties. Functional photosensitizers range from organic and inorganic complexes to nanomaterials as well as the biological photosystem I complex. The focus is then on the three distinct approaches that have emerged for the activation of P450 enzymes. The first approach utilizes the in situ generation of reactive oxygen species entering the P450 mechanism via the peroxide shunt pathway. The other two approaches are sustained by electron injections into catalytically competent heme domains either facilitated by redox partners or through direct heme domain reduction. Achievements as well as pitfalls of each approach are briefly summarized. This article is part of a Special Issue entitled: Cytochrome P450 biodiversity and biotechnology, edited by Erika Plettner, Gianfranco Gilardi, Luet Wong, Vlada Urlacher, Jared Goldstone.

Mechanistic basis of electron transfer to cytochromes p450 by natural redox partners and artificial donor constructs

Cytochromes P450 (P450s) are hemoproteins catalyzing oxidative biotransformation of a vast array of natural and xenobiotic compounds. Reducing equivalents required for dioxygen cleavage and substrate hydroxylation originate from different redox partners including diflavin reductases, flavodoxins, ferredoxins and phthalate dioxygenase reductase (PDR)-type proteins. Accordingly, circumstantial analysis of structural and physicochemical features governing donor-acceptor recognition and electron transfer poses an intriguing challenge. Thus, conformational flexibility reflected by togging between closed and open states of solvent exposed patches on the redox components was shown to be instrumental to steered electron transmission. Here, the membrane-interactive tails of the P450 enzymes and donor proteins were recognized to be crucial to proper orientation toward each other of surface sites on the redox modules steering functional coupling. Also, mobile electron shuttling may come into play. While charge-pairing mechanisms are of primary importance in attraction and complexation of the redox partners, hydrophobic and van der Waals cohesion forces play a minor role in docking events. Due to catalytic plasticity of P450 enzymes, there is considerable promise in biotechnological applications. Here, deeper insight into the mechanistic basis of the redox machinery will permit optimization of redox processes via directed evolution and DNA shuffling. Thus, creation of hybrid systems by fusion of the modified heme domain of P450s with proteinaceous electron carriers helps obviate the tedious reconstitution procedure and induces novel activities. Also, P450-based amperometric biosensors may open new vistas in pharmaceutical and clinical implementation and environmental monitoring.

Cofactor-free light-driven whole-cell cytochrome P450 catalysis

Cytochromes P450 can catalyze various regioselective and stereospecific oxidation reactions of non-functionalized hydrocarbons. Here, we have designed a novel light-driven platform for cofactor-free, whole-cell P450 photo-biocatalysis using eosin Y (EY) as a photosensitizer. EY can easily enter into the cytoplasm of Escherichia coli and bind specifically to the heme domain of P450. The catalytic turnover of P450 was mediated through the direct transfer of photoinduced electrons from the photosensitized EY to the P450 heme domain under visible light illumination. The photoactivation of the P450 catalytic cycle in the absence of cofactors and redox partners is successfully conducted using many bacterial P450s (variants of P450 BM3) and human P450s (CYPs 1A1, 1A2, 1B1, 2A6, 2E1, and 3A4) for the bioconversion of different substrates, including marketed drugs (simvastatin, lovastatin, and omeprazole) and a steroid (17β-estradiol), to demonstrate the general applicability of the light-driven, cofactor-free system.

Cytochrome P450 enzyme functionalized-quantum dots as photocatalysts for drug metabolism

A light-controlled drug metabolism system was successfully designed by using cytochrome P450 2C9 (CYP2C9) functionalized CdTe QDs as photocatalysts.

Photocatalytic activity of protein-conjugated CdS nanoparticles

Colloidal CdS nanoparticles are conjugated with a variety of proteins, including enhanced yellow fluorescent protein, tobacco etch virus protease (TEV), lysozyme, and bacterial cytochrome P450 CYP152A1, and the photochemical properties of the resulting conjugates are analyzed by EPR spectroscopy and hydroxyl radical-specific fluorimetric assay. While irradiation of bare CdS colloids leads to photogeneration of hydroxyl and superoxide radicals, it is surprisingly observed that coating of the CdS particles with proteins effectively suppresses the production of these radical species and instead leads to increased formation of a long-lived reactive oxygen species, most likely H(2)O(2). A mechanism for the observed results is suggested. The empirical results are capitalized on for the assembly of a CdS-TEV nanohybrid, which shows significantly higher performance as a photocatalytic mediator for fatty acid hydroxylation by CYP152A1 than bare CdS nanoparticles.

Tuning of peroxidase activity by covalently tethered DNA oligonucleotides

We report on the modulation of the peroxidase activity of hybrid catalysts, comprising short DNA oligonucleotides and heme enzymes by means of sequence variation of tethered oligonucleotides. In particular, binary mixtures of native heme (protophorphyrin IX) and single-stranded DNA oligonucleotides as well as the analogous covalent heme-oligonucleotide conjugates were compared with DNA-enzyme conjugates, prepared by reconstitution of apo-myoglobin or apo-horseradisch peroxidase, using the aforementioned covalent heme-oligonucleotide conjugates. In all systems, it was clearly evident that the implemented oligonucleotides markedly influence the catalytic activity in a sequence-dependent matter. Greater than 100-fold changes in catalytic constants were observed, depending on which oligonucleotide was incorporated in the hybrid catalyst. We also observed that the tethered oligomers affect the inhibition of HRP-mediated peroxidation by means of small molecule inhibitors. On the basis of the quantitative description of this phenomenon and consideration of the current state of knowledge, we hypothesize that distinct interactions, such as hydrogen bonding or electrostatic contacts, occur between the oligonucleotides and the heme-containing catalyst, which account for the effects observed.

Screening for cytochrome p450 reactivity by harnessing catalase as reporter enzyme

Cytochrome P450 enzymes are known to catalyze a variety of reactions that are difficult to perform by standard organic synthesis, such as the oxidation of unactivated C--C bonds. Cytochrome P450 enzymes can also be used in artificial systems in which organic peroxides act as cosubstrates. To find substrates that are converted by a certain P450 catalyst in the presence of an organic peroxide, various screening assays have been established, however, most of them are limited to one or only a few specific substrates. Here, we report a simple and rapid screening assay that works independently of the nature of the substrate and utilizes a previously undescribed reactivity of catalase as reporter enzyme. In an initial demonstration of this assay, we screened 180 enzyme/peroxide/substrate combinations for potential bioconversions. As shown by subsequent verification of the screening results with liquid chromatography/multistage mass spectrometry (LC/MS(n)), we were able to identify three new substrates for the enzyme CYP152A1 and at least two previously undescribed conversions by the enzyme CYP119.

Apoenzyme reconstitution as a chemical tool for structural enzymology and biotechnology

Many enzymes contain a nondiffusible organic cofactor, often termed a prosthetic group, which is located in the active site and essential for the catalytic activity of the enzyme. These cofactors can often be extracted from the protein to yield the respective apoenzyme, which can subsequently be reconstituted with an artificial analogue of the native cofactor. Nowadays a large variety of synthetic cofactors can be used for the reconstitution of apoenzymes and, thus, generate novel semisynthetic enzymes. This approach has been refined over the past decades to become a versatile tool of structural enzymology to elucidate structure-function relationships of enzymes. Moreover, the reconstitution of apoenzymes can also be used to generate enzymes possessing enhanced or even entirely new functionality. This Review gives an overview on historical developments and the current state-of-the-art on apoenzyme reconstitution.