Ward, T.R.

Chem. Sci. 2016, 7, 673-677, 10.1039/c5sc03116h

Introduction of a biotinylated monophosphine palladium complex within streptavidin affords an enantioselective artificial Suzukiase. Site-directed mutagenesis allowed the optimization of the activity and the enantioselectivity of this artificial metalloenzyme. A variety of atropisomeric biaryls were produced in good yields and up to 90% ee.

Arada, H.; Yamaguchi, H.

Chem. Commun. 2020, 56, 1605-1607, 10.1039/c9cc08756g

We report the first preparation of a monoclonal antibody (mAb) that can immobilize a palladium (Pd)-complex. The allylic amination reaction using a supramolecular catalyst of the Pd-complex with mAb selectively gives the (R)-enantiomer product.

Ward, T.R.

Angew. Chem. Int. Ed. 2008, 47, 701-705, 10.1002/anie.200703159

Palladium in the active site: The incorporation of a biotinylated palladium diphosphine within streptavidin yielded an artificial metalloenzyme for the title reaction (see scheme). Chemogenetic optimization of the catalyst by the introduction of a spacer (red star) between biotin (green triangle) and palladium and saturation mutagenesis at position S112X afforded both R‐ and S‐selective artificial asymmetric allylic alkylases.

Ward, T.R.

J. Am. Chem. Soc. 2003, 125, 9030-9031, 10.1021/ja035545i

Homogeneous and enzymatic catalysis offer complementary means to generate enantiomerically pure compounds. Incorporation of achiral biotinylated rhodium−diphosphine complexes into (strept)avidin yields artificial metalloenzymes for the hydrogenation of N-protected dehydroamino acids. A chemogenetic optimization procedure allows one to produce (R)-acetamidoalanine with 96% enantioselectivity. These hybrid catalysts display features reminiscent both of enzymatic and of homogeneous systems.

Ward, T.R.

J. Am. Chem. Soc. 2004, 126, 14411-14418, 10.1021/ja0476718

We report on the generation of artificial metalloenzymes based on the noncovalent incorporation of biotinylated rhodium−diphosphine complexes in (strept)avidin as host proteins. A chemogenetic optimization procedure allows one to optimize the enantioselectivity for the reduction of acetamidoacrylic acid (up to 96% ee (R) in streptavidin S112G and up to 80% ee (S) in WT avidin). The association constant between a prototypical cationic biotinylated rhodium−diphosphine catalyst precursor and the host proteins was determined at neutral pH:  log Ka = 7.7 for avidin (pI = 10.4) and log Ka = 7.1 for streptavidin (pI = 6.4). It is shown that the optimal operating conditions for the enantioselective reduction are 5 bar at 30 °C with a 1% catalyst loading.

Kamer, P.C.J.

ChemBioChem 2010, 11, 1236-1239, 10.1002/cbic.201000159

Pinning phosphines on proteins: A method for the cysteine‐selective bioconjugation of phosphines has been developed. The photoactive yellow protein has been site‐selectively functionalized with phosphine ligands and phosphine transition metal complexes to afford artificial metalloenzymes that are active in palladium‐catalysed allylic nucleophilic substitution reactions.

Apfel, U.-P.; Happe, T.; Kurisu, G.

Chem. Sci. 2016, 7, 959-968, 10.1039/C5SC03397G

Crystal structures of semisynthetic [FeFe]-hydrogenases with variations in the [2Fe] cluster show little structural differences despite strong effects on activity.

Harada, A.

Org. Biomol. Chem. 2006, 4, 3571, 10.1039/B609242J

Monoclonal antibodies have been elicited against an achiral rhodium complex and this complex was used in the presence of a resultant antibody, 1G8, for the catalytic hydrogenation of 2-acetamidoacrylic acid to produce N-acetyl-L-alanine in high (>98%) enantiomeric excess.

Chan, A.S.C.

Tetrahedron: Asymmetry 1999, 10, 1887-1893, 10.1016/S0957-4166(99)00193-7

The construction of a chiral catalyst system embedded at a specific site in a protein has been studied. The preparation of the biotinylated Pyrphos–Rh(I) complex attached to the binding site in avidin and its application to the asymmetric hydrogenation of itaconic acid have been investigated. By introducing the chiral Pyrphos–Rh(I) moiety into the constrained environment of the protein cavity it was found that the enantioselectivity of the system was significantly influenced by the tertiary conformation within the avidin cavity. The effects of reaction conditions such as temperature, hydrogen pressure, and the pH value of the buffer on enantioselectivity are reported.

Ward, T.R.

Chem. Commun. 2005, 4815, 10.1039/b509015f

Incorporation of biotinylated-[rhodium(diphosphine)]+ complexes, with enantiopure amino acid spacers, in streptavidin affords solvent-tolerant and selective artificial metalloenzymes: up to 91% ee (S) in the hydrogenation of N-protected dehydroamino acids.

Whitesides, G.M.

J. Am. Chem. Soc. 1978, 100, 306-307, 10.1021/ja00469a064

n/a

Reetz, M.T.

Chem. Commun. 2006, 4318, 10.1039/b610461d

The concept of utilizing the methods of directed evolution for tuning the enantioselectivity of synthetic achiral metal–ligand centers anchored to proteins has been implemented experimentally for the first time.

Jarvis, A.G.

ACS Catal. 2021, 11, 3620-3627, 10.1021/acscatal.0c05413

Protein engineering has shown widespread use in improving the industrial application of enzymes and broadening the conditions they are able to operate under by increasing their thermostability and solvent tolerance. Here, we show that protein engineering can be used to increase the thermostability of an artificial metalloenzyme. Thermostable variants of the human steroid carrier protein 2L, modified to bind a metal catalyst, were created by rational design using structural data and a 3DM database. These variants were tested to identify mutations that enhanced the stability of the protein scaffold, and a significant increase in melting temperature was observed with a number of modified metalloenzymes. The ability to withstand higher reaction temperatures resulted in an increased activity in the hydroformylation of 1-octene, with more than fivefold improvement in turnover number, whereas the selectivity for linear aldehyde remained high up to 80%.

Lubitz, W.; Reijerse, E.

Biochemistry 2015, 54, 1474-1483, 10.1021/bi501391d

[FeFe]-hydrogenases are to date the only enzymes for which it has been demonstrated that the native inorganic binuclear cofactor of the active site Fe2(adt)(CO)3(CN)2 (adt = azadithiolate = [S-CH2-NH-CH2-S]2–) can be synthesized on the laboratory bench and subsequently inserted into the unmaturated enzyme to yield fully functional holo-enzyme (Berggren, G. et al. (2013) Nature 499, 66–70; Esselborn, J. et al. (2013) Nat. Chem. Biol. 9, 607–610). In the current study, we exploit this procedure to introduce non-native cofactors into the enzyme. Mimics of the binuclear subcluster with a modified bridging dithiolate ligand (thiodithiolate, N-methylazadithiolate, dimethyl-azadithiolate) and three variants containing only one CN– ligand were inserted into the active site of the enzyme. We investigated the activity of these variants for hydrogen oxidation as well as proton reduction and their structural accommodation within the active site was analyzed using Fourier transform infrared spectroscopy. Interestingly, the monocyanide variant with the azadithiolate bridge showed ∼50% of the native enzyme activity. This would suggest that the CN– ligands are not essential for catalytic activity, but rather serve to anchor the binuclear subsite inside the protein pocket through hydrogen bonding. The inserted artificial cofactors with a propanedithiolate and an N-methylazadithiolate bridge as well as their monocyanide variants also showed residual activity. However, these activities were less than 1% of the native enzyme. Our findings indicate that even small changes in the dithiolate bridge of the binuclear subsite lead to a rather strong decrease of the catalytic activity. We conclude that both the Brønsted base function and the conformational flexibility of the native azadithiolate amine moiety are essential for the high catalytic activity of the native enzyme.

de Vries, J.

Chem. Commun. 2005, 5656, 10.1039/B512138H

Papain, modified at Cys-25 with a monodentate phosphite ligand and complexed with Rh(COD)2BF4, is an active catalyst in the hydrogenation of methyl 2-acetamidoacrylate.

Eppinger, J.

ChemistryOpen 2013, 2, 50-54, 10.1002/open.201200044

How to train a protein: Metal‐conjugated affinity labels were used to selectively position catalytically active metal centers in the binding pocket of proteases. The resulting artificial metalloenzymes achieve up to 82 % e.r. in the hydrogenation of ketones. The modular setup enables a rapid generation of artificial metalloenzyme libraries, which can be adapted to a broad range of catalytic conditions.

Onoda, A.

ACS Catal. 2014, 4, 2645-2648, 10.1021/cs500392e

The hydrogen-evolving diiron complex, (μ-S)2Fe2(CO)6 with a tethered maleimide moiety was synthesized and covalently embedded within the cavity of a rigid β-barrel protein matrix by coupling a maleimide moiety to a cysteine residue within the β-barrel. The (μ-S)2Fe2(CO)6 core within the cavity was characterized by UV–vis absorption and a characteristic CO vibration determined by IR measurements. The diiron complex embedded within the cavity retains the necessary catalytic activity (TON up to 130 for 6 h) to evolve H2 via a photocatalytic cycle with a Ru photosensitizer in a solution of 100 mM ascorbate and 50 mM Tris/HCl at pH 4.0 and 25 °C.

Tiede, D.M.; Utschig, L.M.

J. Am. Chem. Soc. 2013, 135, 13246-13249, 10.1021/ja405277g

The direct conversion of sunlight into fuel is a promising means for the production of storable renewable energy. Herein, we use Nature’s specialized photosynthetic machinery found in the Photosystem I (PSI) protein to drive solar fuel production from a nickel diphosphine molecular catalyst. Upon exposure to visible light, a self-assembled PSI-[Ni(P2PhN2Ph)2](BF4)2 hybrid generates H2 at a rate 2 orders of magnitude greater than rates reported for photosensitizer/[Ni(P2PhN2Ph)2](BF4)2 systems. The protein environment enables photocatalysis at pH 6.3 in completely aqueous conditions. In addition, we have developed a strategy for incorporating the Ni molecular catalyst with the native acceptor protein of PSI, flavodoxin. Photocatalysis experiments with this modified flavodoxin demonstrate a new mechanism for biohybrid creation that involves protein-directed delivery of a molecular catalyst to the reducing side of Photosystem I for light-driven catalysis. This work further establishes strategies for constructing functional, inexpensive, earth-abundant solar fuel-producing PSI hybrids that use light to rapidly produce hydrogen directly from water.

Ward, T.R.

Adv. Synth. Catal. 2007, 349, 1923-1930, 10.1002/adsc.200700022

We report on our efforts to create efficient artificial metalloenzymes for the enantioselective hydrogenation of N‐protected dehydroamino acids using either avidin or streptavidin as host proteins. Introduction of chiral amino acid spacers – phenylalanine or proline – between the biotin anchor and the flexible aminodiphosphine moiety 1, combined with saturation mutagenesis at position S112X of streptavidin, affords second generation artificial hydrogenases displaying improved organic solvent tolerance, reaction rates (3‐fold) and (S)‐selectivities (up to 95 % ee for N‐acetamidoalanine and N‐acetamidophenylalanine). It is shown that these artificial metalloenzymes follow Michaelis–Menten kinetics with an increased affinity for the substrate and a higher kcat than the protein‐free catalyst (compare kcat 3.06 min−1 and KM 7.38 mM for [Rh(COD)Biot‐1]+ with kcat 12.30 min−1 and KM 4.36 mM for [Rh(COD)Biot‐(R)‐Pro‐1]+ ⊂ WT Sav). Finally, we present a straightforward protocol using Biotin‐Sepharose to immobilize artificial metalloenzymes (>92 % ee for N‐acetamidoalanine and N‐acetamidophenylalanine using [Rh(COD)Biot‐(R)‐Pro‐1]+ ⊂ Sav S112W).

Ward, T.R.

C. R. Chim. 2007, 10, 678-683, 10.1016/j.crci.2007.02.020

We report on our efforts to create efficient artificial metalloenzymes for the enantioselective hydrogenation of N-protected dehydroamino acids using streptavidin as host protein. Introduction of an (R)-proline spacer between the biotin anchor and the diphosphine moiety affords a versatile ligand Biot-(R)-Pro-1 which displays good (S)-selectivities in the presence of streptavidin (91% ee). The resulting artificial metalloenzyme [Rh(Biot-(R)-Pro-1)(COD)]+ ⊂ WT-Sav displays increased stability against organic solvents.

Happe, T.

Nat. Chem. Biol. 2013, 9, 607-609, 10.1038/Nchembio.1311

Hydrogenases catalyze the formation of hydrogen. The cofactor ('H-cluster') of [FeFe]-hydrogenases consists of a [4Fe-4S] cluster bridged to a unique [2Fe] subcluster whose biosynthesis in vivo requires hydrogenase-specific maturases. Here we show that a chemical mimic of the [2Fe] subcluster can reconstitute apo-hydrogenase to full activity, independent of helper proteins. The assembled H-cluster is virtually indistinguishable from the native cofactor. This procedure will be a powerful tool for developing new artificial H2-producing catalysts.

Fontecilla-Camps, J.C.

Eur. J. Inorg. Chem. 2013, 2013, 3596-3600, 10.1002/ejic.201300592

The crystal structure of bovine β‐lactoglobulin bound to a complex consisting of a (η5‐Cp*)Rh(2,2′‐dipyridylamine) head and a lauric acid derived hydrophobic tail has been solved at 1.85 Å resolution. Previous work has shown that this hybrid catalyzes the transfer hydrogenation of an aryl ketone in neat water with formate as hydrogen donor with enantiomeric excess (ee) of about 26 %. Calculations using the X‐ray model indicate that the complex head can adopt discrete conformations, which may explain the ee observed.

Kamer, P.C.J.; Laan, W.

Dalton Trans. 2010, 39, 8477, 10.1039/c0dt00239a

The preparation of hybrid transition metalloproteins by thiol-selective incorporation of organometallic rhodium- and ruthenium complexes is described. Phosphine ligands and two rhodium-diphosphine complexes bearing a carboxylic acid group were coupled to the cysteine of PYP R52G, yielding a metalloenzyme active in the rhodium catalyzed hydrogenation of dimethyl itaconate. The successful coupling was shown by 31P NMR spectroscopy and ESI mass spectroscopy. In addition wild-type PYP (PYP WT), PYP R52G and ALBP were successfully modified with a (η6-arene) ruthenium(II) phenanthroline complex via a maleimide linker.

Ward, T.R.

Angew. Chem. Int. Ed. 2005, 44, 7764-7767, 10.1002/anie.200502000

The combination of chemical‐ with genetic‐optimization strategies (i.e. chemogenetic) allows the production of artificial hydrogenases based on the biotin–avidin technology. In the spirit of enzymes, second‐coordination‐sphere interactions between the host protein (streptavidin) and the substrate (an olefin) allow fine‐tuning of the selectivity to produce either R or S hydrogenation products.