46 publications

46 publications

Abiological Catalysis by Artificial Haem Proteins Containing Noble Metals in Place of Iron

Hartwig, J.F.

Nature 2016, 534, 534-537, 10.1038/nature17968

Enzymes that contain metal ions—that is, metalloenzymes—possess the reactivity of a transition metal centre and the potential of molecular evolution to modulate the reactivity and substrate-selectivity of the system1. By exploiting substrate promiscuity and protein engineering, the scope of reactions catalysed by native metalloenzymes has been expanded recently to include abiological transformations2,3. However, this strategy is limited by the inherent reactivity of metal centres in native metalloenzymes. To overcome this limitation, artificial metalloproteins have been created by incorporating complete, noble-metal complexes within proteins lacking native metal sites1,4,5. The interactions of the substrate with the protein in these systems are, however, distinct from those with the native protein because the metal complex occupies the substrate binding site. At the intersection of these approaches lies a third strategy, in which the native metal of a metalloenzyme is replaced with an abiological metal with reactivity different from that of the metal in a native protein6,7,8. This strategy could create artificial enzymes for abiological catalysis within the natural substrate binding site of an enzyme that can be subjected to directed evolution. Here we report the formal replacement of iron in Fe-porphyrin IX (Fe-PIX) proteins with abiological, noble metals to create enzymes that catalyse reactions not catalysed by native Fe-enzymes or other metalloenzymes9,10. In particular, we prepared modified myoglobins containing an Ir(Me) site that catalyse the functionalization of C–H bonds to form C–C bonds by carbene insertion and add carbenes to both β-substituted vinylarenes and unactivated aliphatic α-olefins. We conducted directed evolution of the Ir(Me)-myoglobin and generated mutants that form either enantiomer of the products of C–H insertion and catalyse the enantio- and diastereoselective cyclopropanation of unactivated olefins. The presented method of preparing artificial haem proteins containing abiological metal porphyrins sets the stage for the generation of artificial enzymes from innumerable combinations of PIX-protein scaffolds and unnatural metal cofactors to catalyse a wide range of abiological transformations.


Metal: Ir
Ligand type: Methyl; Porphyrin
Host protein: Myoglobin (Mb)
Anchoring strategy: Metal substitution
Optimization: Chemical & genetic
Reaction: C-H activation
Max TON: 7260
ee: 68
PDB: ---
Notes: ---

Metal: Ir
Ligand type: Methyl; Porphyrin
Host protein: Myoglobin (Mb)
Anchoring strategy: Metal substitution
Optimization: Chemical & genetic
Reaction: C-H activation
Max TON: 92
ee: 84
PDB: ---
Notes: ---

A "Broad Spectrum" Carbene Transferase for Synthesis of Chiral α-Trifluoromethylated Organoborons

Roelfes, G.

ACS Cent. Sci. 2019, 5, 206-208, 10.1021/acscentsci.9b00015

Directed evolution generated an enzyme for the enantioselective synthesis of α-trifluoromethylated organoborons—potentially attractive synthons for fluorinated compounds.


Metal: Fe
Ligand type: Porphyrin
Host protein: Cytochrome c
Anchoring strategy: Native
Optimization: Genetic
Reaction: B-H insertion
Max TON: 2900
ee: 95
PDB: ---
Notes: ---

A Clamp-Like Biohybrid Catalyst for DNA Oxidation

Nolte, R.J.M.

Nat. Chem. 2013, 5, 945-951, 10.1038/NCHEM.1752

In processive catalysis, a catalyst binds to a substrate and remains bound as it performs several consecutive reactions, as exemplified by DNA polymerases. Processivity is essential in nature and is often mediated by a clamp-like structure that physically tethers the catalyst to its (polymeric) template. In the case of the bacteriophage T4 replisome, a dedicated clamp protein acts as a processivity mediator by encircling DNA and subsequently recruiting its polymerase. Here we use this DNA-binding protein to construct a biohybrid catalyst. Conjugation of the clamp protein to a chemical catalyst with sequence-specific oxidation behaviour formed a catalytic clamp that can be loaded onto a DNA plasmid. The catalytic activity of the biohybrid catalyst was visualized using a procedure based on an atomic force microscopy method that detects and spatially locates oxidized sites in DNA. Varying the experimental conditions enabled switching between processive and distributive catalysis and influencing the sliding direction of this rotaxane-like catalyst.


Metal: Mn
Ligand type: Porphyrin
Host protein: gp45
Anchoring strategy: Covalent
Optimization: ---
Max TON: ---
ee: ---
PDB: 1CZD
Notes: ---

A Designed Heme-[4Fe-4S] Metalloenzyme Catalyzes Sulfite Reduction like the Native Enzyme

Lu, Y.

Science 2018, 361, 1098-1101, 10.1126/science.aat8474

Multielectron redox reactions often require multicofactor metalloenzymes to facilitate coupled electron and proton movement, but it is challenging to design artificial enzymes to catalyze these important reactions, owing to their structural and functional complexity. We report a designed heteronuclear heme-[4Fe-4S] cofactor in cytochrome c peroxidase as a structural and functional model of the enzyme sulfite reductase. The initial model exhibits spectroscopic and ligand-binding properties of the native enzyme, and sulfite reduction activity was improved—through rational tuning of the secondary sphere interactions around the [4Fe-4S] and the substrate-binding sites—to be close to that of the native enzyme. By offering insight into the requirements for a demanding six-electron, seven-proton reaction that has so far eluded synthetic catalysts, this study provides strategies for designing highly functional multicofactor artificial enzymes.


Metal: Fe
Host protein: Cytochrome c peroxidase
Anchoring strategy: Dative
Optimization: Chemical & genetic
Reaction: Sulfite reduction
Max TON: ---
ee: ---
PDB: ---
Notes: Designed heteronuclear heme-[4Fe-4S] cofactor in cytochrome c peroxidase

An Artificial Metalloenzyme with the Kinetics of Native Enzymes

Hartwig, J.F.

Science 2016, 354, 102-106, 10.1126/science.aah4427

Natural enzymes contain highly evolved active sites that lead to fast rates and high selectivities. Although artificial metalloenzymes have been developed that catalyze abiological transformations with high stereoselectivity, the activities of these artificial enzymes are much lower than those of natural enzymes. Here, we report a reconstituted artificial metalloenzyme containing an iridium porphyrin that exhibits kinetic parameters similar to those of natural enzymes. In particular, variants of the P450 enzyme CYP119 containing iridium in place of iron catalyze insertions of carbenes into C–H bonds with up to 98% enantiomeric excess, 35,000 turnovers, and 2550 hours−1 turnover frequency. This activity leads to intramolecular carbene insertions into unactivated C–H bonds and intermolecular carbene insertions into C–H bonds. These results lift the restrictions on merging chemical catalysis and biocatalysis to create highly active, productive, and selective metalloenzymes for abiological reactions.


Metal: Ir
Ligand type: Methyl; Porphyrin
Host protein: Cytochrome P450 (CYP119)
Anchoring strategy: Metal substitution
Optimization: Chemical & genetic
Reaction: C-H activation
Max TON: 582
ee: 98
PDB: ---
Notes: ---

Metal: Ir
Ligand type: Methyl; Porphyrin
Host protein: Cytochrome P450 (CYP119)
Anchoring strategy: Metal substitution
Optimization: Chemical & genetic
Reaction: C-H activation
Max TON: 35129
ee: 91
PDB: ---
Notes: ---

A Noncanonical Proximal Heme Ligand Affords an Efficient Peroxidase in a Globin Fold

Green, A.P.; Hilvert, D.

J. Am. Chem. Soc. 2018, 140, 1535-1543, 10.1021/jacs.7b12621

Expanding the range of genetically encoded metal coordination environments accessible within tunable protein scaffolds presents excellent opportunities for the creation of metalloenzymes with augmented properties and novel activities. Here, we demonstrate that installation of a noncanonical Nδ-methyl histidine (NMH) as the proximal heme ligand in the oxygen binding protein myoglobin (Mb) leads to substantial increases in heme redox potential and promiscuous peroxidase activity. Structural characterization of this catalytically modified myoglobin variant (Mb NMH) revealed significant changes in the proximal pocket, including alterations to hydrogen-bonding interactions involving the prosthetic porphyrin cofactor. Further optimization of Mb NMH via a combination of rational modification and several rounds of laboratory evolution afforded efficient peroxidase biocatalysts within a globin fold, with activities comparable to those displayed by nature’s peroxidases.


Metal: Fe
Host protein: Myoglobin (Mb)
Anchoring strategy: Supramolecular
Optimization: Chemical & genetic
Reaction: Oxidation
Max TON: ~1650
ee: ---
PDB: 5OJ9
Notes: Oxidation of amplex red

Antibody-Metalloporphyrin Catalytic Assembly Mimics Natural Oxidation Enzymes

Keinan, E.

J. Am. Chem. Soc. 1999, 121, 8978-8982, 10.1021/ja990314q

An antibody−metalloporphyrin assembly that catalyzes the enantioselective oxidation of aromatic sulfides to sulfoxides is presented. Antibody SN37.4 was elicited against a water-soluble tin(IV) porphyrin containing an axial α-naphthoxy ligand. The catalytic assembly comprising antibody SN37.4 and a ruthenium(II) porphyrin cofactor exhibited typical enzyme characteristics, such as predetermined oxidant and substrate selectivity, enantioselective delivery of oxygen to the substrate, and Michaelis−Menten saturation kinetics. This assembly, which promotes a complex, multistep catalytic event, represents a close model of natural heme-dependent oxidation enzymes.


Metal: Ru
Ligand type: Porphyrin
Host protein: Antibody SN37.4
Anchoring strategy: Supramolecular
Optimization: Chemical
Reaction: Sulfoxidation
Max TON: 750
ee: 43
PDB: ---
Notes: ---

Artificial Heme Enzymes for the Construction of Gold-Based Biomaterials

Lombardi, A.; Nastri, F.

Int. J. Mol. Sci. 2018, 19, 2896, 10.3390/ijms19102896

Many efforts are continuously devoted to the construction of hybrid biomaterials for specific applications, by immobilizing enzymes on different types of surfaces and/or nanomaterials. In addition, advances in computational, molecular and structural biology have led to a variety of strategies for designing and engineering artificial enzymes with defined catalytic properties. Here, we report the conjugation of an artificial heme enzyme (MIMO) with lipoic acid (LA) as a building block for the development of gold-based biomaterials. We show that the artificial MIMO@LA can be successfully conjugated to gold nanoparticles or immobilized onto gold electrode surfaces, displaying quasi-reversible redox properties and peroxidase activity. The results of this work open interesting perspectives toward the development of new totally-synthetic catalytic biomaterials for application in biotechnology and biomedicine, expanding the range of the biomolecular component aside from traditional native enzymes.


Metal: Fe
Ligand type: Amino acid; Porphyrin
Anchoring strategy: Covalent
Optimization: Chemical & genetic
Reaction: Oxidation
Max TON: ---
ee: ---
PDB: ---
Notes: Immobilization of the ArM on gold surfaces via a lipoic acid anchor.

Artificial Peroxidase-Like Hemoproteins Based on Antibodies Constructed from a Specifically Designed Ortho-Carboxy Substituted Tetraarylporphyrin Hapten and Exhibiting a High Affinity for Iron-Porphyrins

Mahy, J.-P.

FEBS Lett. 1996, 395, 73-76, 10.1016/0014-5793(96)01006-X

In order to get catalytic antibodies modelling peroxidases BALB/c mice have been immunized with iron(III)α,α,α,β‐mesotetrakis‐orthocarboxyphenyl‐porphyrin (Fe(ToCPP))‐KLH conjugates. Monoclonal antibodies have been produced by the hybridoma technology. Three antibodies, 2 IgG, and 1 IgG2a, were found to bind both Fe(ToCPP) and the free base ToCPPH2 with similar binding constants. None of those antibodies was found to bind tetraphenylporphyrin. Those results suggest that the recognition of Fe(ToCPP) by the antibodies was mainly due to the binding of the carboxylate groups to some amino acid residues of the protein. True K d values of 2.9 × 10−9 M and 5.5 × 10−9 M have been determined for the two IgG1‐Fe(ToCPP) complexes. Those values are the best ones ever reported for iron‐porphyrin‐antibody complexes. UV‐vis. studies have shown that the two IgG1‐Fe(ToCPP) complexes were highspin hexacoordinate iron(III) complexes, with no amino acid residue binding the iron, whereas the IgG2α‐Fe(ToCPP) complex was a low‐spin hexacoordinate iron(III) complex with two strong ligands binding the iron atom. Both IgG1 ‐Fe(ToCPP) complexes were found to catalyze the oxidation of 2,2′‐azinobis (3ethylbenzothiazoline‐6‐sulfonic acid (ABTS) 5‐fold more efficiently than Fe(ToCPP) alone whereas the binding of IgG2a to this iron‐porphyrin had no effect on its catalytic activity. k cat values of 100 min−1 and 63 min−1 and k cat/K m. values of 105 M−1 s−1 and 119 M−1 s−1 have been found respectively for the two IgG1‐Fe(ToCPP) complexes.


Metal: Fe
Ligand type: Porphyrin
Host protein: Antibody 13G10
Anchoring strategy: Supramolecular
Optimization: ---
Max TON: ---
ee: ---
PDB: ---
Notes: kcat/KM = 105 M-1 * s-1

Beyond Iron: Iridium-Containing P450 Enzymes for Selective Cyclopropanations of Structurally Diverse Alkenes

Hartwig, J.F.

ACS Cent. Sci. 2017, 3, 302-308, 10.1021/acscentsci.6b00391

Enzymes catalyze organic transformations with exquisite levels of selectivity, including chemoselectivity, stereoselectivity, and substrate selectivity, but the types of reactions catalyzed by enzymes are more limited than those of chemical catalysts. Thus, the convergence of chemical catalysis and biocatalysis can enable enzymatic systems to catalyze abiological reactions with high selectivity. Recently, we disclosed artificial enzymes constructed from the apo form of heme proteins and iridium porphyrins that catalyze the insertion of carbenes into a C–H bond. We postulated that the same type of Ir(Me)-PIX enzymes could catalyze the cyclopropanation of a broad range of alkenes with control of multiple modes of selectivity. Here, we report the evolution of artificial enzymes that are highly active and highly stereoselective for the addition of carbenes to a wide range of alkenes. These enzymes catalyze the cyclopropanation of terminal and internal, activated and unactivated, electron-rich and electron-deficient, conjugated and nonconjugated alkenes. In particular, Ir(Me)-PIX enzymes derived from CYP119 catalyze highly enantio- and diastereoselective cyclopropanations of styrene with ±98% ee, >70:1 dr, >75% yield, and ∼10,000 turnovers (TON), as well as 1,2-disubstituted styrenes with up to 99% ee, 35:1 dr, and 54% yield. Moreover, Ir(Me)-PIX enzymes catalyze cyclopropanation of internal, unactivated alkenes with up to 99% stereoselectivity, 76% yield, and 1300 TON. They also catalyze cyclopropanation of natural products with diastereoselectivities that are complementary to those attained with standard transition metal catalysts. Finally, Ir(Me)-PIX P450 variants react with substrate selectivity that is reminiscent of natural enzymes; they react preferentially with less reactive internal alkenes in the presence of more reactive terminal alkenes. Together, the studies reveal the suitability of Ir-containing P450s to combine the broad reactivity and substrate scope of transition metal catalysts with the exquisite selectivity of enzymes, generating catalysts that enable reactions to occur with levels and modes of activity and selectivity previously unattainable with natural enzymes or transition metal complexes alone.


Metal: Ir
Ligand type: Methyl; Porphyrin
Host protein: Cytochrome P450 (CYP119)
Anchoring strategy: Metal substitution
Optimization: Chemical & genetic
Reaction: Cyclopropanation
Max TON: 10181
ee: 98
PDB: ---
Notes: Selectivity for cis product (cis/trans = 90:1)

Capture and Characterization of a Reactive Haem– Carbenoid Complex in an Artificial Metalloenzyme

Hilvert, D.

Nat. Catal. 2018, 1, 578-584, 10.1038/s41929-018-0105-6

Non-canonical amino acid ligands are useful for fine-tuning the catalytic properties of metalloenzymes. Here, we show that recombinant replacement of the histidine ligand proximal to haem in myoglobin with Nδ-methylhistidine enhances the protein’s promiscuous carbene-transfer chemistry, enabling efficient styrene cyclopropanation in the absence of reductant, even under aerobic conditions. The increased electrophilicity of the modified Fe(iii) centre, combined with subtle structural adjustments at the active site, allows direct attack of ethyl diazoacetate to produce a reactive carbenoid adduct, which has an unusual bridging Fe(iii)–C–N(pyrrole) configuration as shown by X-ray crystallography. Quantum chemical calculations suggest that the bridged complex equilibrates with the more reactive end-on isomer, ensuring efficient cyclopropanation. These findings underscore the potential of non-canonical ligands for extending the capabilities of metalloenzymes by opening up new reaction pathways and facilitating the characterization of reactive species that would not otherwise accumulate.


Metal: Fe
Host protein: Myoglobin (Mb)
Anchoring strategy: ---
Optimization: Genetic
Reaction: Cyclopropanation
Max TON: 1000
ee: 99
PDB: 6F17
Notes: Structure of the Mb*(NMH) haem-iron complex

Metal: Fe
Host protein: Myoglobin (Mb)
Anchoring strategy: ---
Optimization: Genetic
Reaction: Cyclopropanation
Max TON: 1000
ee: 99
PDB: 6G5B
Notes: Structure of the Mb*(NMH) haem-iron–carbenoid complex

Catalytic Reduction of NO to N2O by a Designed Heme Copper Center in Myoglobin: Implications for the Role of Metal Ions

Lu, Y.

J. Am. Chem. Soc. 2006, 128, 6766-6767, 10.1021/ja058822p

The effects of metal ions on the reduction of nitric oxide (NO) with a designed heme copper center in myoglobin (F43H/L29H sperm whale Mb, CuBMb) were investigated under reducing anaerobic conditions using UV−vis and EPR spectroscopic techniques as well as GC/MS. In the presence of Cu(I), catalytic reduction of NO to N2O by CuBMb was observed with turnover number of 2 mol NO·mol CuBMb-1·min-1, close to 3 mol NO·mol enzyme-1·min-1 reported for the ba3 oxidases from T. thermophilus. Formation of a His-heme-NO species was detected by UV−vis and EPR spectroscopy. In comparison to the EPR spectra of ferrous-CuBMb-NO in the absence of metal ions, the EPR spectra of ferrous-CuBMb-NO in the presence of Cu(I) showed less-resolved hyperfine splitting from the proximal histidine, probably due to weakening of the proximal His-heme bond. In the presence of Zn(II), formation of a five-coordinate ferrous-CuBMb-NO species, resulting from cleavage of the proximal heme Fe-His bond, was shown by UV−vis and EPR spectroscopic studies. The reduction of NO to N2O was not observed in the presence of Zn(II). Control experiments using wild-type myoglobin indicated no reduction of NO in the presence of either Cu(I) or Zn(II). These results suggest that both the identity and the oxidation state of the metal ion in the CuB center are important for NO reduction. A redox-active metal ion is required to deliver electrons, and a higher oxidation state is preferred to weaken the heme iron−proximal histidine toward a five-coordinate key intermediate in NO reduction.


Metal: Cu
Ligand type: Amino acid; Porphyrin
Host protein: Myoglobin (Mb)
Anchoring strategy: Dative
Optimization: Genetic
Max TON: 2400
ee: ---
PDB: ---
Notes: Sperm whale myoglobin

Chemoselective, Enzymatic C−H Bond Amination Catalyzed by a Cytochrome P450 Containing an Ir(Me)-PIX Cofactor

Hartwig, J.F.

J. Am. Chem. Soc. 2017, 139, 1750-1753, 10.1021/jacs.6b11410

Cytochrome P450 enzymes have been engineered to catalyze abiological C–H bond amination reactions, but the yields of these reactions have been limited by low chemoselectivity for the amination of C–H bonds over competing reduction of the azide substrate to a sulfonamide. Here we report that P450s derived from a thermophilic organism and containing an iridium porphyrin cofactor (Ir(Me)-PIX) in place of the heme catalyze enantioselective intramolecular C−H bond amination reactions of sulfonyl azides. These reactions occur with chemoselectivity for insertion of the nitrene units into C−H bonds over reduction of the azides to the sulfonamides that is higher and with substrate scope that is broader than those of enzymes containing iron porphyrins. The products from C−H amination are formed in up to 98% yield and ∼300 TON. In one case, the enantiomeric excess reaches 95:5 er, and the reactions can occur with divergent site selectivity. The chemoselectivity for C–H bond amination is greater than 20:1 in all cases. Variants of the Ir(Me)-PIX CYP119 displaying these properties were identified rapidly by evaluating CYP119 mutants containing Ir(Me)-PIX in cell lysates, rather than as purified enzymes. This study sets the stage to discover suitable enzymes to catalyze challenging C–H amination reactions.


Metal: Ir
Ligand type: Methyl; Porphyrin
Host protein: Cytochrome P450 (CYP119)
Anchoring strategy: Metal substitution
Optimization: Chemical & genetic
Reaction: C-H activation
Max TON: 294
ee: 26
PDB: ---
Notes: ---

Metal: Ir
Ligand type: Methyl; Porphyrin
Host protein: Cytochrome P450 (CYP119)
Anchoring strategy: Metal substitution
Optimization: Chemical & genetic
Reaction: C-H activation
Max TON: 192
ee: 95
PDB: ---
Notes: ---

Construction and In Vivo Assembly of a Catalytically Proficient and Hyperthermostable De Novo Enzyme

Anderson, J.L.R.

Nat. Commun. 2017, 8, 10.1038/s41467-017-00541-4

Although catalytic mechanisms in natural enzymes are well understood, achieving the diverse palette of reaction chemistries in re-engineered native proteins has proved challenging. Wholesale modification of natural enzymes is potentially compromised by their intrinsic complexity, which often obscures the underlying principles governing biocatalytic efficiency. The maquette approach can circumvent this complexity by combining a robust de novo designed chassis with a design process that avoids atomistic mimicry of natural proteins. Here, we apply this method to the construction of a highly efficient, promiscuous, and thermostable artificial enzyme that catalyzes a diverse array of substrate oxidations coupled to the reduction of H2O2. The maquette exhibits kinetics that match and even surpass those of certain natural peroxidases, retains its activity at elevated temperature and in the presence of organic solvents, and provides a simple platform for interrogating catalytic intermediates common to natural heme-containing enzymes.


Metal: Fe
Ligand type: Porphyrin
Anchoring strategy: Supramolecular
Optimization: Genetic
Reaction: Oxidation
Max TON: ---
ee: ---
PDB: ---
Notes: Oxidation of 2,2′-azino-bis(3-ethylbenzothiazo-line-6-sulfonic acid (ABTS)

Coordination Chemistry of Iron(III)-Porphyrin-Antibody Complexes Influence on the Peroxidase Activity of the Axial Coordination of an Imidazole on the Iron Atom

Mahy, J.-P.

Eur. J. Biochem. 2002, 269, 470-480, 10.1046/j.0014-2956.2001.02670.x

An artificial peroxidase‐like hemoprotein has been obtained by associating a monoclonal antibody, 13G10, and its iron(III)–α,α,α,β‐meso‐tetrakis(ortho‐carboxyphenyl)porphyrin [Fe(ToCPP)] hapten. In this antibody, about two‐thirds of the porphyrin moiety is inserted in the binding site, its ortho‐COOH substituents being recognized by amino‐acids of the protein, and a carboxylic acid side chain of the protein acts as a general acid base catalyst in the heterolytic cleavage of the O–O bond of H2O2, but no amino‐acid residue is acting as an axial ligand of the iron. We here show that the iron of 13G10–Fe(ToCPP) is able to bind, like that of free Fe(ToCPP), two small ligands such as CN–, but only one imidazole ligand, in contrast to to the iron(III) of␣Fe(ToCPP) that binds two. This phenomenon is general for a series of monosubstituted imidazoles, the 2‐ and 4‐alkyl‐substituted imidazoles being the best ligands, in agreement with the hydrophobic character of the antibody binding site. Complexes of antibody 13G10 with less hindered iron(III)–tetraarylporphyrins bearing only one [Fe(MoCPP)] or two meso‐[ortho‐carboxyphenyl] substituents [Fe(DoCPP)] also bind only one imidazole. Finally, peroxidase activity studies show that imidazole inhibits the peroxidase activity of 13G10–Fe(ToCPP) whereas it increases that of 13G10–Fe(DoCPP). This could be interpreted by the binding of the imidazole ligand on the iron atom which probably occurs in the case of 13G10–Fe(ToCPP) on the less hindered face of the porphyrin, close to the catalytic COOH residue, whereas in the case of 13G10–Fe(DoCPP) it can occur on the other face of the porphyrin. The 13G10–Fe(DoCPP)–imidazole complex thus constitutes a nice artificial peroxidase‐like hemoprotein, with the axial imidazole ligand of the iron mimicking the proximal histidine of peroxidases and a COOH side chain of the antibody acting as a general acid‐base catalyst like the distal histidine of peroxidases does.


Metal: Fe
Ligand type: Porphyrin
Host protein: Antibody 13G10
Anchoring strategy: Supramolecular
Optimization: ---
Max TON: ---
ee: ---
PDB: ---
Notes: kcat/KM = 15200 M-1 * s-1

Coordination Chemistry Studies and Peroxidase Activity of a New Artificial Metalloenzyme Built by the “Trojan Horse” Strategy

Mahy, J.-P.

J. Mol. Catal. A: Chem. 2010, 317, 19-26, 10.1016/j.molcata.2009.10.016

In the general context of green chemistry, a considerable research effort is devoted to the elaboration of new artificial metalloproteins that catalyze, under mild conditions, the oxidation of a wide range of organic compounds, using cheap and environmentally friendly oxidants. A new artificial hemoprotein was obtained by the so-called “Trojan horse” strategy involving the non-covalent insertion of a cationic iron–porphyrin–estradiol cofactor into an anti-estradiol antibody. UV–vis titrations showed the formation of a 1/2 antibody/cofactor complex with a dissociation constant KD = 4.10−7 M. UV–vis determination of the Fe-imidazole binding constants showed that the protein provided a weak steric hindrance around the iron–porphyrin cofactor. The antibody–estradiol–iron–porphyrin complex displayed a peroxidase activity and catalyzed the oxidation of ABTS by H2O2 with about double the efficiency of the iron–porphyrin–estradiol alone. Kinetic studies revealed that this was due to a faster formation of the intermediate high valent iron–oxo species in the presence of the antibody protein. Consequently, the association of an anti-estradiol antibody with an iron–porphyrin–estradiol cofactor leads to a new artificial hemoprotein with an interesting peroxidase activity and the “Trojan horse” strategy appears as a valuable method to generate artificial metalloenzymes that could act as biocatalysts for selective oxidations.


Metal: Fe
Ligand type: Porphyrin
Host protein: Antibody 7A3
Anchoring strategy: Supramolecular
Optimization: ---
Max TON: ---
ee: ---
PDB: ---
Notes: k1 = 574 M-1 * min-1

Crystal Structure of Two Anti-Porphyrin Antibodies with Peroxidase Activity

Golinelli-Pimpaneau, B.

PLoS One 2012, 7, e51128, 10.1371/journal.pone.0051128

We report the crystal structures at 2.05 and 2.45 Å resolution of two antibodies, 13G10 and 14H7, directed against an iron(III)-αααβ-carboxyphenylporphyrin, which display some peroxidase activity. Although these two antibodies differ by only one amino acid in their variable λ-light chain and display 86% sequence identity in their variable heavy chain, their complementary determining regions (CDR) CDRH1 and CDRH3 adopt very different conformations. The presence of Met or Leu residues at positions preceding residue H101 in CDRH3 in 13G10 and 14H7, respectively, yields to shallow combining sites pockets with different shapes that are mainly hydrophobic. The hapten and other carboxyphenyl-derivatized iron(III)-porphyrins have been modeled in the active sites of both antibodies using protein ligand docking with the program GOLD. The hapten is maintained in the antibody pockets of 13G10 and 14H7 by a strong network of hydrogen bonds with two or three carboxylates of the carboxyphenyl substituents of the porphyrin, respectively, as well as numerous stacking and van der Waals interactions with the very hydrophobic CDRH3. However, no amino acid residue was found to chelate the iron. Modeling also allows us to rationalize the recognition of alternative porphyrinic cofactors by the 13G10 and 14H7 antibodies and the effect of imidazole binding on the peroxidase activity of the 13G10/porphyrin complexes.


Metal: Fe
Ligand type: Porphyrin
Host protein: Antibody 13G10
Anchoring strategy: Antibody
Optimization: Chemical & genetic
Reaction: Peroxidation
Max TON: ---
ee: ---
PDB: 4AMK
Notes: ---

Metal: Fe
Ligand type: Porphyrin
Host protein: Antibody 14H7
Anchoring strategy: Antibody
Optimization: Chemical & genetic
Reaction: Peroxidation
Max TON: ---
ee: ---
PDB: 4AT6
Notes: ---

Defining the Role of Tyrosine and Rational Tuning of Oxidase Activity by Genetic Incorporation of Unnatural Tyrosine Analogs

Lu, Y.; Wang, J.

J. Am. Chem. Soc. 2015, 137, 4594-4597, 10.1021/ja5109936

While a conserved tyrosine (Tyr) is found in oxidases, the roles of phenol ring pKa and reduction potential in O2 reduction have not been defined despite many years of research on numerous oxidases and their models. These issues represent major challenges in our understanding of O2 reduction mechanism in bioenergetics. Through genetic incorporation of unnatural amino acid analogs of Tyr, with progressively decreasing pKa of the phenol ring and increasing reduction potential, in the active site of a functional model of oxidase in myoglobin, a linear dependence of both the O2 reduction activity and the fraction of H2O formation with the pKa of the phenol ring has been established. By using these unnatural amino acids as spectroscopic probe, we have provided conclusive evidence for the location of a Tyr radical generated during reaction with H2O2, by the distinctive hyperfine splitting patterns of the halogenated tyrosines and one of its deuterated derivatives incorporated at the 33 position of the protein. These results demonstrate for the first time that enhancing the proton donation ability of the Tyr enhances the oxidase activity, allowing the Tyr analogs to augment enzymatic activity beyond that of natural Tyr.


Metal: Cu
Ligand type: Porphyrin
Host protein: Myoglobin (Mb)
Anchoring strategy: Dative
Optimization: Chemical & genetic
Max TON: 1200
ee: ---
PDB: 4FWX
Notes: Sperm whale myoglobin

Enzyme stabilization via computationally guided protein stapling

Fasan, R.; Khare, S.D.

Proc. Natl. Acad. Sci. U. S. A. 2017, 114, 12472-12477, 10.1073/pnas.1708907114

Thermostabilization represents a critical and often obligatory step toward enhancing the robustness of enzymes for organic synthesis and other applications. While directed evolution methods have provided valuable tools for this purpose, these protocols are laborious and time-consuming and typically require the accumulation of several mutations, potentially at the expense of catalytic function. Here, we report a minimally invasive strategy for enzyme stabilization that relies on the installation of genetically encoded, nonreducible covalent staples in a target protein scaffold using computational design. This methodology enables the rapid development of myoglobin-based cyclopropanation biocatalysts featuring dramatically enhanced thermostability (ΔTm = +18.0 °C and ΔT50 = +16.0 °C) as well as increased stability against chemical denaturation [ΔCm (GndHCl) = 0.53 M], without altering their catalytic efficiency and stereoselectivity properties. In addition, the stabilized variants offer superior performance and selectivity compared with the parent enzyme in the presence of a high concentration of organic cosolvents, enabling the more efficient cyclopropanation of a water-insoluble substrate. This work introduces and validates an approach for protein stabilization which should be applicable to a variety of other proteins and enzymes.


Metal: Fe
Ligand type: Porphyrin
Host protein: Myoglobin (Mb)
Anchoring strategy: Supramolecular
Optimization: Chemical & genetic
Reaction: Cyclopropanation
Max TON: 4740
ee: 99.2
PDB: ---
Notes: Stapling of protein via thioether bond formation between the noncanonical amino acid O-2-bromoethyl tyrosine and cysteine

Flavohemoglobin: A Semisynthetic Hydroxylase Acting in the Absence of Reductase

Kaiser, E.T.

J. Am. Chem. Soc. 1987, 109, 606-607, 10.1021/ja00236a062

n/a


Metal: Fe
Ligand type: Porphyrin
Host protein: Hemoglobin
Anchoring strategy: ---
Optimization: ---
Max TON: ---
ee: ---
PDB: ---
Notes: ---

Helichrome: Synthesis and Enzymatic Activity of a Designed Hemeprotein

Kaiser, E.T.; Sasaki, T.

J. Am. Chem. Soc. 1989, 111, 380-381, 10.1021/ja00183a065

n/a


Metal: Fe
Ligand type: Porphyrin
Host protein: Artificial construct
Anchoring strategy: Covalent
Optimization: ---
Max TON: ---
ee: ---
PDB: ---
Notes: Only 60 amino acids

Hemoabzymes: Towards New Biocatalysts for Selective Oxidations

Mahy, J.-P.

J. Immunol. Methods 2002, 269, 39-57, 10.1016/S0022-1759(02)00223-5

Catalytic antibodies with a metalloporphyrin cofactor or «hemoabzymes», used as models for hemoproteins like peroxidases and cytochrome P450, represent a promising route to catalysts tailored for selective oxidation reactions. A brief overview of the literature shows that until now, the first strategy for obtaining such artificial hemoproteins has been to produce antiporphyrin antibodies, raised against various free-base, N-substituted Sn-, Pd- or Fe-porphyrins. Five of them exhibited, in the presence of the corresponding Fe-porphyrin cofactor, a significant peroxidase activity, with kcat/Km values of 3.7×103–2.9×105 M−1 min−1. This value remained, however, low when compared to that of peroxidases. This strategy has also led to a few models of cytochrome P450. The best of them, raised against a water-soluble tin(IV) porphyrin containing an axial α-naphtoxy ligand, was reported to catalyze the stereoselective oxidation of aromatic sulfides by iodosyl benzene using a Ru(II)-porphyrin cofactor. The relatively low efficiency of the porphyrin–antibody complexes is probably due, at least in part, to the fact that no proximal ligand of Fe has been induced in those antibodies. We then proposed to use, as a hapten, microperoxidase 8 (MP8), a heme octapeptide in which the imidazole side chain of histidine 18 acts as a proximal ligand of the iron atom. This led to the production of seven antibodies recognizing MP8, the best of them, 3A3, binding it with an apparent binding constant of 10−7 M. The corresponding 3A3–MP8 complex was found to have a good peroxidase activity characterized by a kcat/Km value of 2×106 M−1 min−1, which constitutes the best one ever reported for an antibody–porphyrin complex. Active site topology studies suggest that the binding of MP8 occurs through interactions of its carboxylate substituents with amino acids of the antibody and that the protein brings a partial steric hindrance of the distal face of the heme of MP8. Consequently, the use of the 3A3–MP8 complexes for the selective oxidation of substrates, such as sulfides, alkanes and alkenes will be undertaken in the future.


Metal: Fe
Ligand type: Porphyrin
Host protein: Antibody 3A3
Anchoring strategy: Supramolecular
Optimization: ---
Max TON: ---
ee: ---
PDB: ---
Notes: kcat/KM = 33000 M-1 * s-1

Hemozymes Peroxidase Activity Of Artificial Hemoproteins Constructed From the Streptomyces Lividans Xylanase A and Iron(III)-Carboxy-Substituted Porphyrins

Mahy, J.-P.

Bioconjug. Chem. 2008, 19, 899-910, 10.1021/bc700435a

To develop artificial hemoproteins that could lead to new selective oxidation biocatalysts, a strategy based on the insertion of various iron-porphyrin cofactors into Xylanase A (Xln10A) was chosen. This protein has a globally positive charge and a wide enough active site to accommodate metalloporphyrins that possess negatively charged substituents such as microperoxidase 8 (MP8), iron(III)-tetra-α4-ortho-carboxyphenylporphyrin (Fe(ToCPP)), and iron(III)-tetra-para-carboxyphenylporphyrin (Fe(TpCPP)). Coordination chemistry of the iron atom and molecular modeling studies showed that only Fe(TpCPP) was able to insert deeply into Xln10A, with a KD value of about 0.5 µM. Accordingly, Fe(TpCPP)-Xln10A bound only one imidazole molecule, whereas Fe(TpCPP) free in solution was able to bind two, and the UV–visible spectrum of the Fe(TpCPP)-Xln10A-imidazole complex suggested the binding of an amino acid of the protein on the iron atom, trans to the imidazole. Fe(TpCPP)-Xln10A was found to have peroxidase activity, as it was able to catalyze the oxidation of typical peroxidase cosubstrates such as guaiacol and o-dianisidine by H2O2. With these two cosubstrates, the KM value measured with the Fe(TpCPP)-Xln10A complex was higher than those values observed with free Fe(TpCPP), probably because of the steric hindrance and the increased hydrophobicity caused by the protein around the iron atom of the porphyrin. The peroxidase activity was inhibited by imidazole, and a study of the pH dependence of the oxidation of o-dianisidine suggested that an amino acid with a pKA of around 7.5 was participating in the catalysis. Finally, a very interesting protective effect against oxidative degradation of the porphyrin was provided by the protein.


Metal: Fe
Ligand type: Porphyrin
Host protein: Xylanase A (XynA)
Anchoring strategy: Supramolecular
Optimization: ---
Max TON: ---
ee: ---
PDB: ---
Notes: kcat/KM = 1083 M-1 * s-1

Incorporation of Manganese Complexes into Xylanase: New Artificial Metalloenzymes for Enantioselective Epoxidation

Mahy, J.-P.; Ricoux, R.

ChemBioChem 2012, 13, 240-251, 10.1002/cbic.201100659

Enantioselective epoxidation: An artificial metalloenzyme obtained by noncovalent insertion of MnIII‐meso‐tetrakis(para‐carboxyphenyl)porphyrin Mn(TpCPP) into xylanase 10A from Streptomyces lividans as a host protein was able to catalyse the oxidation of para‐methoxystyrene by KHSO5 with a 16 % yield and the best enantioselectivity (80 % in favour of the R isomer) ever reported for an artificial metalloenzyme.


Metal: Mn
Ligand type: Porphyrin
Host protein: Xylanase A (XynA)
Anchoring strategy: Supramolecular
Optimization: ---
Reaction: Epoxidation
Max TON: 21
ee: 80
PDB: ---
Notes: ---

Intramolecular C(sp3)-H Amination of Arylsulfonyl Azides with Engineered and Artificial Myoglobin-Based Catalysts

Fasan, R.

Bioorg. Med. Chem. 2014, 22, 5697-5704, 10.1016/j.bmc.2014.05.015

The direct conversion of aliphatic CH bonds into CN bonds provides an attractive approach to the introduction of nitrogen-containing functionalities in organic molecules. Following the recent discovery that cytochrome P450 enzymes can catalyze the cyclization of arylsulfonyl azide compounds via an intramolecular C(sp3)H amination reaction, we have explored here the CH amination reactivity of other hemoproteins. Various heme-containing proteins, and in particular myoglobin and horseradish peroxidase, were found to be capable of catalyzing this transformation. Based on this finding, a series of engineered and artificial myoglobin variants containing active site mutations and non-native Mn- and Co-protoporphyrin IX cofactors, respectively, were prepared to investigate the effect of these structural changes on the catalytic activity and selectivity of these catalysts. Our studies showed that metallo-substituted myoglobins constitute viable CH amination catalysts, revealing a distinctive reactivity trend as compared to synthetic metalloporphyrin counterparts. On the other hand, amino acid substitutions at the level of the heme pocket were found to be beneficial toward improving the stereo- and enantioselectivity of these Mb-catalyzed reactions. Mechanistic studies involving kinetic isotope effect experiments indicate that CH bond cleavage is implicated in the rate-limiting step of myoglobin-catalyzed amination of arylsulfonyl azides. Altogether, these studies indicate that myoglobin constitutes a promising scaffold for the design and development of CH amination catalysts.


Metal: Mn
Ligand type: Amino acid; Porphyrin
Host protein: Myoglobin (Mb)
Anchoring strategy: Metal substitution
Optimization: Chemical & genetic
Reaction: C-H activation
Max TON: 142
ee: ---
PDB: ---
Notes: ---

Iron-porphyrin Catalyzed Carbene Transfer Reactions – an Evolution fro Biomimetic Catalysis towards Chemistry-inspired Non-natural Reactivities of Enzymes

Koenigs, R.M.; Weissenborn, M.J.

ChemCatChem 2020, 10.1002/cctc.201901565

Bioinspired, synthetic porphyrin complexes are important catalysts in organic synthesis and play a pivotal role in efficient carbene transfer reactions. The advances in this research area stimulated recent, “chemo‐inspired” developments in biocatalysis. Today, both synthetic iron complexes and enzymes play an important role to conduct carbene transfer reactions. The advances and potential developments in both research areas are discussed in this concept article.


Metal: Fe
Ligand type: Porphyrin
Host protein: ---
Anchoring strategy: ---
Optimization: Chemical & genetic
Reaction: Carbene insertion
Max TON: ---
ee: ---
PDB: ---
Notes: ---

Neocarzinostatin-Based Hybrid Biocatalysts for Oxidation Reactions

Mahy, J.-P.; Ricoux, R.

Dalton Trans. 2014, 43, 8344-8354, 10.1039/c4dt00151f

An anionic iron(III)-porphyrin–testosterone conjugate 1-Fe has been synthesized and fully characterized. It has been further associated with a neocarzinostatin variant, NCS-3.24, to generate a new artificial metalloenzyme following the so-called ‘Trojan Horse’ strategy. This new 1-Fe-NCS-3.24 biocatalyst showed an interesting catalytic activity as it was found able to catalyze the chemoselective and slightly enantioselective (ee = 13%) sulfoxidation of thioanisole by H2O2. Molecular modelling studies show that a synergy between the binding of the steroid moiety and that of the porphyrin macrocycle into the protein binding site can explain the experimental results, indicating a better affinity of 1-Fe for the NCS-3.24 variant than testosterone and testosterone-hemisuccinate themselves. They also show that the Fe-porphyrin complex is sandwiched between the two subdomains of the protein providing with good complementarities. However, the artificial cofactor entirely fills the cavity and its metal ion remains widely exposed to the solvent which explains the moderate enantioselectivity observed. Some possible improvements in the “Trojan Horse” strategy for obtaining better catalysts of selective oxidations are presented.


Metal: Fe
Ligand type: Porphyrin
Anchoring strategy: Supramolecular
Optimization: ---
Reaction: Sulfoxidation
Max TON: 6
ee: 13
PDB: ---
Notes: ---

New Activities of a Catalytic Antibody with a Peroxidase Activity: Formation of Fe(II)–RNO Complexes and Stereoselective Oxidation of Sulfides

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.


Metal: Fe
Ligand type: Porphyrin
Host protein: Antibody 3A3
Anchoring strategy: Supramolecular
Optimization: ---
Reaction: Sulfoxidation
Max TON: 82
ee: 45
PDB: ---
Notes: ---

Orthogonal Expression of an Artificial Metalloenzyme for Abiotic Catalysis

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.


Metal: Ir
Ligand type: Methyl; Porphyrin
Host protein: Cytochrome BM3h
Anchoring strategy: Reconstitution
Optimization: Chemical & genetic
Reaction: Cyclopropanation
Max TON: 339
ee: 97
PDB: ---
Notes: Reaction of styrene with ethyl diazoacetate, cis:trans = 29:71

Oxidation of Organic Molecules in Homogeneous Aqueous Solution Catalyzed by Hybrid Biocatalysts (Based on the Trojan Horse Strategy)

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.


Metal: Fe
Ligand type: Porphyrin
Host protein: Antibody 7A3
Anchoring strategy: Supramolecular
Optimization: ---
Reaction: Sulfoxidation
Max TON: 9
ee: 10
PDB: ---
Notes: ---

Metal: Mn
Ligand type: Porphyrin
Host protein: Antibody 7A3
Anchoring strategy: Supramolecular
Optimization: ---
Reaction: Epoxidation
Max TON: 105
ee: ---
PDB: ---
Notes: Imidazole as co-catalyst