Mahy, J.-P.

Eur. J. Biochem. 2004, 271, 1277-1283, 10.1111/j.1432-1033.2004.04032.x

In order to estimate the size of the cavity remaining around the heme of the 3A3–microperoxidase 8 (MP8) hemoabzyme, the formation of 3A3–MP8–Fe(II)‐nitrosoalkane complexes upon oxidation of N‐monosubstituted hydroxylamines was examined. This constituted a new reaction for hemoabzymes and is the first example of fully characterized Fe(II)–metabolite complexes of antibody–porphyrin. Also, via a comparison of the reactions with N‐substituted hydroxylamines of various size and hydrophobicity, antibody 3A3 was confirmed to bring about a partial steric hindrance on the distal face of MP8. Subsequently, the influence of the antibody on the stereoselectivity of the S‐oxidation of sulfides was examined. Our results showed that MP8 alone and the antibody–MP8 complex catalyze the oxidation of thioanisole by H2O2 and tert‐butyl hydroperoxide, following a peroxidase‐like two‐step oxygen‐transfer mechanism involving a radical–cation intermediate. The best system, associating H2O2 as oxidant and 3A3–MP8 as a catalyst, in the presence of 5% tert‐butyl alcohol, led to the stereoselective S‐oxidation of thioanisole with a 45% enantiomeric excess in favour of the R isomer. This constitutes the highest enantiomeric excess reported to date for the oxidation of sulfides catalyzed by hemoabzymes.

Mahy, J.-P.

C. R. Chim. 2007, 10, 684-702, 10.1016/j.crci.2006.12.014

Catalytic antibodies with a metalloporphyrin cofactor or “hemoabzymes”, used as models for hemoproteins like peroxidases and cytochrome P450s, represent a promising route to catalysts tailored for selective oxidation reactions. The first strategy has been to produce anti-porphyrin antibodies, raised against various N-substituted- and meso-carboxyaryl-porphyrins, which led to monoclonal antibodies exhibiting, in the presence of the corresponding iron-porphyrin cofactor, a significant peroxidase activity. We ourselves obtained an artificial hemoprotein by associating a monoclonal antibody, 13G10, and its iron(III)-α,α,α,β-meso-tetrakis(ortho-carboxyphenyl)porphyrin (Fe(ToCPP)) hapten, which exhibited a significant peroxidase activity. Biological studies suggested that in this antibody, a carboxylic acid side chain of the protein participated in the catalysis, but no amino acid residue acting as an axial ligand of the iron was detected. Therefore, to provide the iron atom with an axial ligand, we raised antibodies against microperoxidase 8, a heme octapeptide containing a histidine bound to the iron atom. This strategy was successful, as an antibody–microperoxidase 8 complex (3A3–MP8) led to the best kcat/Km ever reported for antibody–porphyrin complexes. The ability of the 3A3–MP8 complex to catalyze the selective oxidation of substrates was studied and it was found able to catalyze the regioselective nitration of aromatics by NO2−/H2O2 as well as the stereoselective oxidation of sulfides like thioanisole by H2O2. Other strategies based on antibodies have to be developed to obtain more efficient biomimetic systems for cytochrome P450s. A first one could involve the modification of anti-substrate antibodies by covalent linkage of an iron(III)-porphyrin close to the binding site of the substrate, to obtain an artificial hemoprotein able to catalyze its regioselective oxidation.

Palomo, J.M.

Biotechnol. Adv. 2015, 33, 605-613, 10.1016/j.biotechadv.2014.12.010

The development of new and successful biotransformation processes of key interest in medicinal and pharmaceutical chemistry involves creating new biocatalysts with improved or even new activities and selectivities. This review emphasizes the new emerging developed strategies to achieve this goal, site-selective chemical modification of enzymes using tailor-made peptides, specific insertion of metals or organometallic complexes into proteins producing bio-catalysts with multiple activities and computational design for creating evolved artificial enzymes with non-natural synthetic catalytic activities.

Acc. Chem. Res. 2002, 35, 35-43, 10.1021/ar000087t

The reconstitution of myoglobin with an artificially created prosthetic group is a unique method for introducing a new chemical function into the protein. Particularly, the modification of two heme-propionates gives us an effective binding domain or binding site on the protein surface. This Account traces the design and construction of the highly ordered binding domain around the entrance of the heme pocket. The discussion includes the protein−small molecule or protein−protein recognition, electron transfer reaction within the complex, and enhancement of the chemical reactivity of the myoglobin with a substrate binding site. The synthetic approach to modifying a protein will be a new trend in engineering a novel function in naturally occurring hemoprotein.

Shafaat, H.S.

J. Phys. Chem. Lett. 2015, 6, 3731-3736, 10.1021/acs.jpclett.5b01750

A simple, functional mimic of [NiFe] hydrogenases based on a nickel-substituted rubredoxin (NiRd) protein is reported. NiRd is capable of light-initiated and solution-phase hydrogen production and demonstrates high electrocatalytic activity using protein film voltammetry. The catalytic voltammograms are modeled using analytical expressions developed for hydrogenase enzymes, revealing maximum turnover frequencies of approximately 20–100 s–1 at 4 °C with an overpotential of 540 mV. These rates are directly comparable to those observed for [NiFe] hydrogenases under similar conditions. Like the native enzymes, the proton reduction activity of NiRd is strongly inhibited by carbon monoxide. This engineered rubredoxin-based enzyme is chemically and thermally robust, easily accessible, and highly tunable. These results have implications for understanding the enzymatic mechanisms of native hydrogenases, and, using NiRd as a scaffold, it will be possible to optimize this catalyst for application in sustainable fuel generation.

Arnold, F.H.

J. Am. Chem. Soc. 2019, 141, 19585-19588, 10.1021/jacs.9b11608

Transition-metal catalysis is a powerful tool for the construction of chemical bonds. Here we show that Pseudomonas savastanoi ethylene-forming enzyme, a non-heme iron enzyme, can catalyze olefin aziridination and nitrene C−H insertion, and that these activities can be improved by directed evolution. The nonheme iron center allows for facile modification of the primary coordination sphere by addition of metalcoordinating molecules, enabling control over enzyme activity and selectivity using small molecules.

Latour, J.-M.

J. Inorg. Biochem. 2021, 225, 111613, 10.1016/j.jinorgbio.2021.111613

Amines are ubiquitous in biology and pharmacy. As a consequence, introducing N functionalities in organic molecules is attracting strong continuous interest. The past decade has witnessed the emergence of very efficient and selective catalytic systems achieving this goal thanks to engineered hemoproteins. In this review, we examine how these enzymes have been engineered focusing rather on the rationale behind it than the methodology employed. These studies are put in perspective with respect to in vitro and in vivo nitrene transfer processes performed by cytochromes P450. An emphasis is put on mechanistic aspects which are confronted to current molecular knowledge of these reactions. Forthcoming developments are delineated.

Hartwig, J.F.

Acc. Chem. Res. 2019, 52, 326-335, 10.1021/acs.accounts.8b00586

Enzymes have evolved to catalyze a range of biochemical transformations with high efficiencies and unparalleled selectivities, including stereoselectivities, regioselectivities, chemoselectivities, and substrate selectivities, while typically operating under mild aqueous conditions. These properties have motivated extensive research to identify or create enzymes with reactivity that complements or even surpasses the reactivity of small-molecule catalysts for chemical reactions. One of the limitations preventing the wider use of enzymes in chemical synthesis, however, is the narrow range of bond constructions catalyzed by native enzymes. One strategy to overcome this limitation is to create artificial metalloenzymes (ArMs) that combine the molecular recognition of nature with the reactivity discovered by chemists. This Account describes a new approach for generating ArMs by the formal replacement of the natural iron found in the porphyrin IX (PIX) of hemoproteins with noble metals. Analytical techniques coupled with studies of chemical reactivity have demonstrated that expression of apomyoglobins and apocytochrome P450s (for which “apo-” denotes the cofactor-free protein) followed by reconstitution with metal−PIX cofactors in vitro creates proteins with little perturbation of the native structure, suggesting that the cofactors likely reside within the native active site. By means of this metal substitution strategy, a large number of ArMs have been constructed that contain varying metalloporphyrins and mutations of the protein. The studies discussed in this Account encompass the use of ArMs containing noble metals to catalyze a range of abiological transformations with high chemoselectivity, enantioselectivity, diastereoselectivity, and regioselectivity. These transformations include intramolecular and intermolecular insertion of carbenes into C−H, N−H, and S−H bonds, cyclopropanation of vinylarenes and of internal and nonconjugated alkenes, and intramolecular insertions of nitrenes into C−H bonds. The rates of intramolecular insertions into C−H bonds catalyzed by thermophilic P450 enzymes reconstituted with an Ir(Me)−PIX cofactor are now comparable to the rates of reactions catalyzed by native enzymes and, to date, 1000 times greater than those of any previously reported ArM. This reactivity also encompasses the selective intermolecular insertion of the carbene from ethyl diazoacetate into C−H bonds over dimerization of the carbene to form alkenes, a class of carbene insertion or selectivity not reported to occur with small-molecule catalysts. These combined results highlight the potential of well-designed ArMs to catalyze abiological transformations that have been challenging to achieve with any type of catalyst. The metal substitution strategy described herein should complement the reactivity of native enzymes and expand the scope of enzyme-catalyzed reactions.

Hilvert, D.

Angew. Chem. Int. Ed. 2021, 60, 15063-15068, 10.1002/anie.202103437

Changing the primary metal coordination sphere is a powerful strategy for tuning metalloprotein properties. Here we used amber stop codon suppression with engineered pyrrolysyl-tRNA synthetases, including two newly evolved enzymes, to replace the proximal histidine in myoglobin with Nδ-methylhistidine, 5-thiazoylalanine, 4-thiazoylalanine and 3-(3-thienyl)alanine. In addition to tuning the heme redox potential over a >200 mV range, these noncanonical ligands modulate the protein's carbene transfer activity with ethyl diazoacetate. Variants with increased reduction potential proved superior for cyclopropanation and N–H insertion, whereas variants with reduced Eo values gave higher S–H insertion activity. Given the functional importance of histidine in many enzymes, these genetically encoded analogues could be valuable tools for probing mechanism and enabling new chemistries.

Lu, Y.

Chem. - Eur. J. 2009, 15, 7481-7489, 10.1002/chem.200802449

To demonstrate protein modulation of metal‐cofactor reactivity through noncovalent interactions, pH‐dependent sulfoxidation and 2,2′‐azino‐bis(3‐ethylbenzthiazoline‐6‐sulphonic acid) (ABTS) oxidation reactivity of a designed myoglobin (Mb) containing non‐native Mn–salen complex (1) was investigated using H2O2 as the oxidant. Incorporation of 1 inside the Mb resulted in an increase in the turnover numbers through exclusion of water from the metal complex and prevention of Mn–salen dimer formation. Interestingly, the presence of protein in itself is not enough to confer the increase activity as mutation of the distal His64 in Mb to Phe to remove hydrogen‐bonding interactions resulted in no increase in the turnover numbers, while mutation His64 to Arg, another residue with ability to hydrogen‐bond interactions, resulted in an increase in reactivity. These results strongly suggest that the distal ligand His64, through its hydrogen‐bonding interaction, plays important roles in enhancing and fine‐tuning reactivity of the Mn–salen complex. Nonlinear least‐squares fitting of rate versus pH plots demonstrates that 1⋅Mb(H64X) (X=H, R and F) and the control Mn–salen 1 exhibit pKa values varying from pH 6.4 to 8.3, and that the lower pKa of the distal ligand in 1⋅Mb(H64X), the higher the reactivity it achieves. Moreover, in addition to the pKa at high pH, 1⋅Mb displays another pKa at low pH, with pKa of 5.0±0.08. A comparison of the effect of different pH on sulfoxidation and ABTS oxidation indicates that, while the intermediate produced at low pH conditions could only perform sulfoxidation, the intermediate at high pH could oxidize both sulfoxides and ABTS. Such a fine‐control of reactivity through hydrogen‐bonding interactions by the distal ligand to bind, orient and activate H2O2 is very important for designing artificial enzymes with dramatic different and tunable reactivity from catalysts without protein scaffolds.

Roelfes, G.

Chem. Sci. 2015, 6, 770-776, 10.1039/c4sc01525h

Artificial metalloenzymes have emerged as an attractive new approach to enantioselective catalysis. Herein, we introduce a novel strategy for preparation of artificial metalloenzymes utilizing amber stop codon suppression methodology for the in vivo incorporation of metal-binding unnatural amino acids. The resulting artificial metalloenzymes were applied in catalytic asymmetric Friedel–Crafts alkylation reactions and up to 83% ee for the product was achieved.

Okuda, J.; Sauer, D.F.

Beilstein J. Org. Chem. 2018, 14, 2861-2871, 10.3762/bjoc.14.265

This review summarizes the recent progress of Grubbs–Hoveyda (GH) type olefin metathesis catalysts incorporated into the robust fold of β-barrel proteins. Anchoring strategies are discussed and challenges and opportunities in this emerging field are shown from simple small-molecule transformations over ring-opening metathesis polymerizations to in vivo olefin metathesis.

Gademann, K.

Commun. Chem. 2018, 1, 10.1038/s42004-018-0087-y

Metal-catalyzed chemical transformations performed at the cellular level bear great potential for the manipulation of biological processes. The complexity of the cell renders the use of transition metal chemistry difficult in cellular systems. The delivery of the reactive catalyst and the control of its spatial localization remain challenging. Here we report the surface functionalization of the unicellular eukaryote Chlamydomonas reinhardtii with a tailor-made artificial metalloenzyme for on-cell catalysis. The functionalized cells remain viable and are able to uncage a fluorogenic substrate on their surface. This work leverages cell surface engineering to provide live cells with new-to-nature reactivity. In addition, this operationally simple approach is not genetically encoded and thereby transient, which offers advantages with regard to temporal control, cell viability, and safety. Therefore, and as a feature, the movement of the functionalized cells can be directed by light (via phototaxis), allowing for the three-dimensional localization of catalysts by outside stimuli.

Tiller, J.C.

ChemCatChem 2016, 8, 593-599, 10.1002/cctc.201501083

The Sharpless dihydroxylation of styrene with the artificial metalloenzyme osmate‐laccase‐poly(2‐methyloxazoline) was investigated to find reaction conditions that allow this unique catalyst to reveal its full potential. After changing the co‐oxidizing agent to tert‐butyl hydroperoxide and optimizing the osmate/enzyme ratio, the turnover frequency and the turnover number could be increased by an order of magnitude, showing that the catalyst can compete with classical organometallic catalysts. Varying the metal in the active center showed that osmate is by far the most active catalytic center, but the reaction can also be realized with permanganate and iron(II) salts.

Ward, T.R.

Protein Engineering Handbook 2012, n/a

n/a

Brustad, E.M.

ChemBioChem 2017, 18, 2380-2384, 10.1002/cbic.201700397

Engineering an (Ir)regular cytochrome P450: Mutations within the heme‐binding pocket of a cytochrome P450 enabled the selective incorporation of an artificial Ir‐porphyrin cofactor into the protein, in cells. This orthogonal metalloprotein showed enhanced behavior in unnatural carbene‐mediated cyclopropanation of aliphatic and electron‐deficient olefins.

Ward, T.R.

Angew. Chem. Int. Ed. 2011, 50, 10863-10866, 10.1002/anie.201103632

Taking control: Selective catalysts for olefin dihydroxylation have been generated by the combination of apo‐streptavidin and OsO4. Site‐directed mutagenesis allows improvement of enantioselectivity and even inversion of enantiopreference in certain cases. Notably allyl phenyl sulfide and cis‐β‐methylstyrene were converted with unprecedented enantiomeric excess.

Lombardi, A.; Maglio, O.; Nastri, F.

Biopolymers 2018, 109, e23107, 10.1002/bip.23107

Inspired by natural heme‐proteins, scientists have attempted for decades to design efficient and selective metalloporphyrin‐based oxidation catalysts. Starting from the pioneering work on small molecule mimics in the late 1970s, we have assisted to a tremendous progress in designing cages of different nature and complexity, able to accommodate metalloporphyrins. With the intent of tuning and controlling their reactivity, more and more sophisticated and diverse environments are continuously exploited. In this review, we will survey the current state of art in oxidation catalysis using iron‐ and manganese‐porphyrins housed within designed or engineered protein cages. We will also examine the innovative metal‐organic framework (MOF) systems, exploited to achieving an enzyme‐like environment around the metalloporphyrin cofactor.

Ménage, S.

Isr. J. Chem. 2015, 55, 61-75, 10.1002/ijch.201400110

The principle of enzyme mimics has been raised to its pinnacle by the design of hybrids made from inorganic complexes embedded into biomolecules. The present review focuses on the design of artificial metalloenzymes for oxidation reactions by oxygen transfer reactions, with a special focus on proteins anchoring inorganic complexes or metal ions via supramolecular interactions. Such reactions are of great interest for the organic synthesis of building blocks. In the first part, following an overview of the different design of artificial enzymes, the review presents contributions to the rational design of efficient hybrid biocatalysts via supramolecular host/guest approaches, based on the nature of the inorganic complex and the nature of the protein, with special attention to the substrate binding. In the second part, the original purpose of artificial metalloenzymes has been twisted to enable the observation of transient intermediates, to decipher metal‐based oxidation mechanisms. The host protein crystals have been used as crystalline molecular‐scale vessels, within which inorganic catalytic reactions have been followed, thanks to X‐ray crystallography. These hybrids should be an alternative to enzymes for sustainable chemistry.

Gross, Z.; Mahy, J.-P.

Dalton Trans. 2016, 45, 706-710, 10.1039/c5dt04158a

Light induced enantioselective oxidation of an organic molecule with water as the oxygen atom source is demonstrated in a system where chirality is induced by a protein, oxygen atom transfer by a manganese corrole, and photocatalysis by ruthenium complexes.

Mahy, J.-P.

Tetrahedron: Asymmetry 2010, 21, 1593-1600, 10.1016/j.tetasy.2010.03.050

New anionic metalloporphyrin–estradiol conjugates have been synthesized and fully characterized, and have been further associated to a monoclonal anti-estradiol antibody 7A3, to generate new artificial metalloenzymes following the so-called ‘Trojan Horse’ strategy. The spectroscopic characteristics and dissociation constants of these complexes were similar to those obtained for the artificial metalloproteins obtained by association of cationic metalloporphyrin–estradiol conjugates to 7A3. This demonstrates that the nature of the porphyrin substituents, anionic or cationic, had little influence on the association with the antibody that is mainly driven by the tight association of the estradiol anchor with the binding pocket of the antibody. These new biocatalysts appeared to have an interesting catalytic activity in oxidation reactions. The iron(III)–anionic-porphyrin–estradiol-antibody complexes were found able to catalyze the chemoselective and slightly enantioselective (ee = 10%) sulfoxidation of sulfides by H2O2. The Mn(III)–porphyrin–estradiol-antibody complexes were found to catalyze the oxidation of styrene by KHSO5, the Mn(III)–cationic-porphyrin–estradiol-antibody complexes even showing the highest yields so far reported for the oxidation of styrene catalyzed by artificial metalloproteins. However, a lack of chemoselectivity and enantioselectivity was observed, which was probably due to a weak interaction of the metalloporphyrin cofactor with the binding pocket of antibody 7A3, as suggested by the similar UV–visible characteristics and catalytic activities obtained with both anionic and cationic porphyrins.

Jarvis, A.G.

J. Inorg. Biochem. 2021, 215, 111317, 10.1016/j.jinorgbio.2020.111317

Palladium catalysed reactions are ubiquitous in synthetic organic chemistry in both organic solvents and aqueous buffers. The broad reactivity of palladium catalysis has drawn interest as a means to conduct orthogonal transformations in biological settings. Successful examples have been shown for protein modification, in vivo drug decaging and as palladium-protein biohybrid catalysts for selective catalysis. Biological media represents a challenging environment for palladium chemistry due to the presence of a multitude of chelators, catalyst poisons and a requirement for milder reaction conditions e.g. lower temperatures. This review looks to identify successful examples of palladium-catalysed reactions in the presence of proteins or cells and analyse solutions to help to overcome the challenges of working in biological systems.

Ward, T.R.

Methods Enzymol. 2016, 539-556, 10.1016/bs.mie.2016.05.037

Artificial metalloenzymes represent an attractive means of combining state-of-the-art transition metal catalysis with the benefits of natural enzymes. Despite the tremendous recent progress in this field, current efforts toward the directed evolution of these hybrid biocatalysts mainly rely on the laborious, individual purification of protein variants rendering the throughput, and hence the outcome of these campaigns feeble. We have recently developed a screening platform for the directed evolution of artificial metalloenzymes based on the streptavidin–biotin technology in the periplasm of the Gram-negative bacterium Escherichia coli. This periplasmic compartmentalization strategy comprises a number of compelling advantages, in particular with respect to artificial metalloenzymes, which lead to a drastic increase in the throughput of screening campaigns and additionally are of unique value for future in vivo applications. Therefore, we highlight here the benefits of this strategy and intend to propose a generalized guideline for the development of novel transition metal-based biocatalysts by directed evolution in order to extend the natural enzymatic repertoire.

Schultz, P.G.

J. Am. Chem. Soc. 1990, 112, 9414-9415, 10.1021/ja00181a065

The specificity and diversity of the immune system have recently been exploited in the generation of antibodies that catalyze a wide variety of chemical reactions.1·2 Several general strategies for the design of catalytic antibodies have emerged, including the use of antibody binding energy to enhance the chemical reactivity of a cofactor or to position a cofactor and a substrate in close proximity.3,4 An intriguing target for antibody-cofactor catalysis is the oxidative reactions characteristic of heme proteins. Here we report that antibodies specific for A-methylmesoporphyrin IX bind iron(III) mesoporphyrin IX and that the resulting complex catalyzes the oxidation of several substrates. These studies are a first step toward the development of selective antibody-heme monooxygenase catalysts.

Harada, A.

Chem. - Eur. J. 2004, 10, 6179-6186, 10.1002/chem.200305692

Peroxidase activity of a complex of water‐soluble cationic metalloporphyrin with anti‐cationic porphyrin antibody is reported. Antibody 12E11G, which was prepared by immunization with a conjugate of 5‐(4‐carboxyphenyl)‐10,15,20‐tris(4‐methylpyridyl)porphine iodide (3MPy1C), bound to tetramethylpyridylporphyrin iron complex (FeIII–TMPyP) with the dissociation constant of 2.6×10−7 M. The complex of antibody 12E11G with FeIII–TMPyP catalyzed oxidation of pyrogallol, catechol, and guaiacol. A Lineweaver–Burk plot for the oxidation of pyrogallol catalyzed by the FeIII–TMPyP–antibody complex showed Km=8.6 mM and kcat=680 min−1. Under the same conditions, Km and kcat for horseradish peroxidase (HRP) were 0.8 mM and 1750 min−1, respectively. Although the binding interaction of the antibody to the substrates was one order lower than that of native HRP, the peroxidase activity of this system was in the same order of magnitude as that of HRP.

J. Am. Chem. Soc. 1999, 121, 7747-7750, 10.1021/ja9841005

Peroxidase activity of a myoglobin reconstituted with a chemically modified heme 1 is reported. The heme 1 bearing a total of eight carboxylates bound to the terminal of propionate side chains is incorporated into apomyoglobin from horse heart to obtain a new reconstituted myoglobin, rMb(1), with a unique binding domain structure. The UV−vis, CD, and NMR spectra of rMb(1) are comparable with those of native myoglobin, nMb. The mixing of rMb(1) with hydrogen peroxide yields a peroxidase compound II-like species, rMb(1)-II, since the spectrum of rMb(1)-II is identical with that observed for nMb. Stoichiometric oxidation of several small molecules by rMb(1)-II, demonstrates the significant reactivity. (i) The oxidation of cationic substrate such as [Ru(NH3)6]2+ by rMb(1)-II is faster than that observed for oxoferryl species of nMb, nMb-II. (ii) Anionic substrates such as ferrocyanide are unsuitable for the oxidation by rMb(1)-II. (iii) Oxidations of catechol, hydroquinone, and guaiacol are dramatically enhanced by rMb(1)-II (14−32-fold) compared to those observed for nMb-II. Thus, the chemical modification of heme-propionates can alter substrate specificity. Steady-state kinetic measurements indicate that both the reactivity and substrate affinity toward guaiacol oxidation by rMb(1) are improved, so that the specificity, kcat/Km, is 13-fold higher than that in nMb. This result strongly suggests that the artificially modified heme-propionates may increase the accessibility of neutral aromatic substrates to the heme active site. The present work demonstrates that the chemical mutation of prosthetic group is a new strategy to create proteins with engineered function.

Harada, A.

Inorg. Chem. 1997, 36, 6099-6102, 10.1021/ic9610849

Antibody 03-1, which was prepared by immunization with meso-tetrakis(4-carboxyphenyl)porphyrin (TCPP) conjugate, has been found to bind strongly to Mn(III)−TCPP and Fe(III)−TCPP complexes with dissociation constants of 4.1 × 10-7 and 1.5 × 10-7 M, respectively, although other monoclonal antibodies raised against TCPP did not bind to these TCPP−metal complexes. The complexes of antibody 03-1 with Mn(III)−TCPP and Fe(III)−TCPP were found to catalyze oxidation of pyrogallol selectively. A Lineweaver-Burk plot for the oxidation of pyrogallol by the antibody−Fe−TCPP complex showed Km = 4.0 mM and kcat = 50 min-1. Studies on the effect of the molar ratio of the antibody to metalloporphyrin on the catalytic activity showed that a 1:1 complex was the most effective for the reaction. The effect of salt (NaCl) on the reaction showed that electrostatic interaction between the antibody and the metalloporphyrin was important for the reaction. The antibody−metalloporphyrin complexes are stable enough to show catalytic activity in the presence of an excess amount of H2O2.

Borovik, A.S.

J. Am. Chem. Soc. 2017, 139, 17289-17292, 10.1021/jacs.7b10452

Copper–hydroperoxido species (CuII–OOH) have been proposed to be key intermediates in biological and synthetic oxidations. Using biotin–streptavidin (Sav) technology, artificial copper proteins have been developed to stabilize a CuII–OOH complex in solution and in crystallo. Stability is achieved because the Sav host provides a local environment around the Cu–OOH that includes a network of hydrogen bonds to the hydroperoxido ligand. Systematic deletions of individual hydrogen bonds to the Cu–OOH complex were accomplished using different Sav variants and demonstrated that stability is achieved with a single hydrogen bond to the proximal O-atom of the hydroperoxido ligand: changing this interaction to only include the distal O-atom produced a reactive variant that oxidized an external substrate.

Alberto, R.; Ward, T.R.

Helv. Chim. Acta 2018, 101, e1800036, 10.1002/hlca.201800036

Photocatalytic hydrogen evolution by an artificial hydrogenase based on the biotin‐streptavidin technology is reported. A biotinylated cobalt pentapyridyl‐based hydrogen evolution catalyst (HEC) was incorporated into different mutants of streptavidin. Catalysis with [Ru(bpy)3]Cl2 as a photosensitizer (PS) and ascorbate as sacrificial electron donor (SED) at different pH values highlighted the impact of close lying amino acids that may act as a proton relay under the reaction conditions (Asp, Arg, Lys). In the presence of a close‐lying lysine residue, both, the rates were improved, and the reaction was initiated much faster. The X‐ray crystal structure of the artificial hydrogenase reveals a distance of 8.8 Å between the closest lying Co‐moieties. We thus suggest that the hydrogen evolution mechanism proceeds via a single Co centre. Our findings highlight that streptavidin is a versatile host protein for the assembly of artificial hydrogenases and their activity can be fine‐tuned via mutagenesis.

Oohora, K.

J. Inorg. Biochem. 2019, 193, 42-51, 10.1016/j.jinorgbio.2019.01.001

Electron transfer (ET) events occurring within metalloprotein complexes are among the most important classes of reactions in biological systems. This report describes a photoinduced electron transfer between Zn porphyrin and Fe porphyrin within a supramolecular cytochrome b562 (Cyt b562) co-assembly or heterodimer with a well-defined rigid structure formed by a metalloporphyrin–heme pocket interaction and a hydrogen-bond network at the protein interface. The photoinduced charge separation (CS: kCS = 320–600 s−1) and subsequent charge recombination (CR: kCR = 580–930 s−1) were observed in both the Cyt b562 co-assembly and the heterodimer. In contrast, interestingly, no ET events were observed in a system comprised of a flexible and structurally-undefined co-assembly and heterodimers which lack the key hydrogen-bond interaction at the protein interface. Moreover, analysis of the kinetic constants of CS and CR of the heterodimer using the Marcus equation suggests that a single-step ET reaction occurs in the system. These findings provide strong support that the rigid hemoprotein-assembling system containing an appropriate hydrogen-bond network at the protein interface is essential for monitoring the ET reaction.