Heme destruction, the main molecular event during the peroxide-mediated inactivation of chloroperoxidase from Caldariomyces fumago

Surface Au-H Species as Self-Generated Prosthetic Groups of a Formate Dehydrogenase-like Au Nanozyme to Engineer Multienzymatic Activities

Although the past decade has witnessed a rapid development of oxidoreductase-mimicking nanozymes, the mimicry of cofactors that play key roles in mediating electron and proton transfer remains limited. This study explores how surface Au-H species conjugated to Au nanoparticles (NPs) that imitate formate dehydrogenase (FDH) can serve as cofactors, analogous to NADH in natural enzymes, offering diverse possibilities for FDH-mimicking Au nanozymes to mimic various enzymes. Once O2 is present, Au-H species assist Au NPs to complete the on-demand H2O2 generation for cascade reactions. Alternatively, when oxidizing organic molecules are introduced as substrates, Au-H species confer nitro reductase- and aldehyde reductase-like activities on Au NPs under anaerobic conditions. Furthermore, similar to the dehydrogenase-NADH complex, Au NPs possessing Au-H species are gifted with esterase-like activity for ester hydrolysis. By revealing that Au-H species are prosthetic groups for FDH-mimicking Au nanozymes, this work may inspire explorations into future self-generated cofactor mimics for nanozymes, thereby circumventing the need for exogenous cofactors.

Enzymatic Bromocyclization of α- and γ-Allenols by Chloroperoxidase from Curvularia inaequalis

Vanadate-dependent chloroperoxidase from Curvularia inaequalis catalyzes 5-endo-trig bromocyclizations of α-allenols to produce valuable halofunctionalized furans as versatile synthetic building blocks. In contrast to other haloperoxidases, also the more challenging 5-exo-trig halocyclizations of γ-allenols succeed with this system even though the scope still remains more narrow. Benefitting from the vanadate chloroperoxidase's high resiliency towards oxidative conditions, cyclization-inducing reactive hypohalite species are generated in situ from bromide salts and hydrogen peroxide. Crucial requirements for high conversions are aqueous biphasic emulsions as reaction media, stabilized by either cationic or non-ionic surfactants.

Ether Oxidation by an Evolved Fungal Heme-Peroxygenase: Insights into Substrate Recognition and Reactivity

Ethers can be found in the environment as structural, active or even pollutant molecules, although their degradation is not efficient under environmental conditions. Fungal unspecific heme-peroxygenases (UPO were reported to degrade low-molecular-weight ethers through an H₂O₂-dependent oxidative cleavage mechanism. Here, we report the oxidation of a series of structurally related aromatic ethers, catalyzed by a laboratory-evolved UPO (PaDa-I) aimed at elucidating the factors influencing this unusual biochemical reaction. Although some of the studied ethers were substrates of the enzyme, they were not efficiently transformed and, as a consequence, secondary reactions (such as the dismutation of H₂O₂ through catalase-like activity and suicide enzyme inactivation) became significant, affecting the oxidation efficiency. The set of reactions that compete during UPO-catalyzed ether oxidation were identified and quantified, in order to find favorable conditions that promote ether oxidation over the secondary reactions.

In situ H2O2 generation methods in the context of enzyme biocatalysis

Hydrogen peroxide is a versatile oxidant that has use in medical and biotechnology industries. Many enzymes require this oxidant as a reaction mediator in order to undergo their oxygenation chemistries. While there is a reliable method for generating hydrogen peroxide via an anthraquinone cycle, there are several advantages for generating hydrogen in situ. As highlighted in this review, this is particularly beneficial in the case of biocatalysts that require hydrogen peroxide as a reaction mediator because the exogenous addition of hydrogen peroxide can damage their reactive heme centers and render them inactive. In addition, generation of hydrogen peroxide in situ does not dilute the reaction mixture and cause solution parameters to change. The environment would also benefit from a hydrogen peroxide synthesis cycle that does not rely on nonrenewable chemicals obtained from fossil fuels. Generation of hydrogen peroxide in situ for biocatalysis using enzymes, bioelectrocatalyis, photocatalysis, and cold temperature plasmas are addressed. Particular emphasis is given to reaction processes that support high total turnover numbers (TTNs) of the hydrogen peroxide-requiring enzymes. Discussion of innovations in the use of hydrogen peroxide-producing enzyme cascades for antimicrobial activity, wastewater effluent treatment, and biosensors are also included.

Nuclear Waste and Biocatalysis: A Sustainable Liaison?

It is well-known that energy-rich radiation induces water splitting, eventually yielding hydrogen peroxide. Synthetic applications, however, are scarce and to the best of our knowledge, the combination of radioactivity with enzyme-catalysis has not been considered yet. Peroxygenases utilize H₂O₂ as an oxidant to promote highly selective oxyfunctionalization reactions but are also irreversibly inactivated in the presence of too high H₂O₂ concentrations. Therefore, there is a need for efficient in situ H₂O₂ generation methods. Here, we show that radiolytic water splitting can be used to promote specific biocatalytic oxyfunctionalization reactions. Parameters influencing the efficiency of the reaction and current limitations are shown. Particularly, oxidative inactivation of the biocatalyst by hydroxyl radicals influences the robustness of the overall reaction. Radical scavengers can alleviate this issue, but eventually, physical separation of the enzymes from the ionizing radiation will be necessary to achieve robust reaction schemes. We demonstrate that nuclear waste can also be used to drive selective, peroxygenase-catalyzed oxyfunctionalization reactions, challenging our view on nuclear waste in terms of sustainability.

Enhanced P450 fatty acid decarboxylase catalysis by glucose oxidase coupling and co-assembly for biofuel generation

Cytochrome P450 OleT is a fatty acid decarboxylase that uses hydrogen peroxide (H₂O₂) to catalyze the production of terminal alkenes, which are industrially important chemicals with biofuel and synthetic applications. Despite its requirement for large turnover levels, high concentrations of H₂O₂ may cause heme group degradation, diminishing enzymatic activity and limiting broad application for synthesis. Here, we report an artificial enzyme cascade composed of glucose oxidase (GOx) and OleT_SA from Staphylococcus aureus for efficient terminal alkene production. By adjusting the ratio of GOx to OleT_SA, the GOx-based tandem catalysis shows significantly improved product yield compared to the H₂O₂ injection method. Moreover, the co-assembly of the GOx/OleT_SA enzymes with a polymer, forming polymer-dual enzymes nanoparticles, displays improved activity compared to the free enzyme. This dual strategy provides a simple and efficient system to transform a naturally abundant feedstock to industrially important chemicals.

Exploring the Role of Phenylalanine Residues in Modulating the Flexibility and Topography of the Active Site in the Peroxygenase Variant PaDa-I

Unspecific peroxygenases (UPOs) are fungal heme-thiolate enzymes able to catalyze a wide range of oxidation reactions, such as peroxidase-like, catalase-like, haloperoxidase-like, and, most interestingly, cytochrome P450-like. One of the most outstanding properties of these enzymes is the ability to catalyze the oxidation a wide range of organic substrates (both aromatic and aliphatic) through cytochrome P450-like reactions (the so-called peroxygenase activity), which involves the insertion of an oxygen atom from hydrogen peroxide. To catalyze this reaction, the substrate must access a channel connecting the bulk solution to the heme group. The composition, shape, and flexibility of this channel surely modulate the catalytic ability of the enzymes in this family. In order to gain an understanding of the role of the residues comprising the channel, mutants derived from PaDa-I, a laboratory-evolved UPO variant from Agrocybe aegerita, were obtained. The two phenylalanine residues at the surface of the channel, which regulate the traffic towards the heme active site, were mutated by less bulky residues (alanine and leucine). The mutants were experimentally characterized, and computational studies (i.e., molecular dynamics (MD)) were performed. The results suggest that these residues are necessary to reduce the flexibility of the region and maintain the topography of the channel.

Addition of new catalytic sites on the surface of versatile peroxidase for enhancement of LRET catalysis

Versatile peroxidase (VP) from Bjerkandera adusta is an enzyme able to oxidize bulky and high-redox substrates trough a Long-Range Electron Transfer (LRET) pathway. In this study, the introduction of radical-forming aromatic amino acids by chemical modification of the protein surface was performed, and the catalytic implications of these additional surface active-sites on the oxidation of 2,6-dimethylphenol, Mn²⁺ and Remazol Brilliant Blue R (RBBR) were determined. These three different substrates are oxidized in different active-sites of enzyme molecule, of which the high redox RBBR the only one that is transformed by an external radical formed on the protein surface. Both catalytic constants k_cat and K_M were significantly affected by the chemical modifications. Tryptophan- and tyrosine-modified VP showed higher catalytic transformation than the unmodified enzyme for RBBR, while the Mn²⁺ oxidation was significantly reduced by all chemical modifications. Electron Paramagnetic Resonance studies demonstrated the formation of additional protein-based radicals after the chemical modification with radical-forming amino acids. In addition, the catalytic rate of the LRET-mediated transformation showed a good correlation with the ionization energy of the additional amino acid on the protein surface.

Peroxide-Induced Liberation of Iron from Heme Switches Catalysis during Luminol Reaction and Causes Loss of Light and Heterodyning of Luminescence Kinetics

The peroxidation of luminol yields bright luminescence when the reaction is catalyzed by heme proteins. However, an excess of peroxide leads to less light and altered luminescence kinetics, an effect commonly referred to as "suicide inactivation". The aim of this study is to present the molecular processes causing this effect. A comprehensive set of data reported here demonstrates that suicide inactivation is due to a peroxide-induced liberation of iron from its coordinating porphyrin. Liberated iron launches catalysis of the reaction at much lower efficiency. The light-yielding efficiencies of different organic and inorganic catalysts are precisely quantified and compared. It is shown that the catalysis by free iron involves superoxide. This is explained by the formation of a ferryl-oxo-iron complex. In this context, a complete reaction mechanism involving a modified Fenton-Haber-Weiss cycle is proposed for the first time. The switch from the highly efficient biogenically catalyzed luminescence to a less efficient inorganically catalyzed reaction is accompanied by a transition from "flash-type" to "glow-type" luminescence kinetics. Ethylenediaminetetraacetic acid-mediated chelation of iron is used to demonstrate this effect and to separate both kinetics. The explanation of kinetic heterodyning is underpinned by mathematical modeling. The results are able to explain the as yet unexplained phenomena discussed in the less recent literature and to settle disputes about them. It is concluded that peroxide concentrations exceeding the level tolerated by the catalyzing heme protein negatively impact performance and precision of luminol-based assays, where the light yield is used as a quantitative measure for analyte concentrations.

Xenobiotic Compounds Degradation by Heterologous Expression of a Trametes sanguineus Laccase in Trichoderma atroviride

Fungal laccases are enzymes that have been studied because of their ability to decolorize and detoxify effluents; they are also used in paper bleaching, synthesis of polymers, bioremediation, etc. In this work we were able to express a laccase from Trametes (Pycnoporus) sanguineus in the filamentous fungus Trichoderma atroviride. For this purpose, a transformation vector was designed to integrate the gene of interest in an intergenic locus near the blu17 terminator region. Although monosporic selection was still necessary, stable integration at the desired locus was achieved. The native signal peptide from T. sanguineus laccase was successful to secrete the recombinant protein into the culture medium. The purified, heterologously expressed laccase maintained similar properties to those observed in the native enzyme (Km and kcat and kcat/km values for ABTS, thermostability, substrate range, pH optimum, etc). To determine the bioremediation potential of this modified strain, the laccase-overexpressing Trichoderma strain was used to remove xenobiotic compounds. Phenolic compounds present in industrial wastewater and bisphenol A (an endocrine disruptor) from the culture medium were more efficiently removed by this modified strain than with the wild type. In addition, the heterologously expressed laccase was able to decolorize different dyes as well as remove benzo[α]pyrene and phenanthrene in vitro, showing its potential for xenobiotic compound degradation.

From amino alcohol to aminopolyol: one-pot multienzyme oxidation and aldol addition

In this work, the successful coupling of enzymatic oxidation and aldol addition reactions for the synthesis of a Cbz-aminopolyol from a Cbz-amino alcohol was achieved for the first time in a multienzymatic one-pot system. The two-step cascade reaction consisted of the oxidation of Cbz-ethanolamine to Cbz-glycinal catalyzed by chloroperoxidase from the fungus Caldariomyces fumago and aldol addition of dihydroxyacetone phosphate to Cbz-glycinal catalyzed by rhamnulose-1-phosphate aldolase expressed as a recombinant enzyme in Escherichia coli, yielding (3R,4S)-5-{[(benzyloxy)carbonyl]amino}-5-deoxy-1-O-phosphonopent-2-ulose. Tools of enzymatic immobilization, reactor configurations, and modification of the reaction medium were applied to highly increase the production of the target compound. While the use of soluble enzymes yielded only 23.6 % of Cbz-aminopolyol due to rapid enzyme inactivation, the use of immobilized ones permitted an almost complete consumption of Cbz-ethanolamine, reaching Cbz-aminopolyol yields of 69.1 and 71.9 % in the stirred-tank and packed-bed reactor, respectively. Furthermore, the reaction production was 18-fold improved when it was catalyzed by immobilized enzymes in the presence of 5 % (v/v) dioxane, reaching a value of 86.6 mM of Cbz-aminopoliol (31 g/L).