9 publications

9 publications

Building Reactive Copper Centers in Human Carbonic Anhydrase II

Emerson, J.P.

J. Biol. Inorg. Chem. 2013, 18, 595-598, 10.1007/s00775-013-1009-1

Reengineering metalloproteins to generate new biologically relevant metal centers is an effective a way to test our understanding of the structural and mechanistic features that steer chemical transformations in biological systems. Here, we report thermodynamic data characterizing the formation of two type-2 copper sites in carbonic anhydrase and experimental evidence showing one of these new, copper centers has characteristics similar to a variety of well-characterized copper centers in synthetic models and enzymatic systems. Human carbonic anhydrase II is known to bind two Cu2+ ions; these binding events were explored using modern isothermal titration calorimetry techniques that have become a proven method to accurately measure metal-binding thermodynamic parameters. The two Cu2+-binding events have different affinities (K a approximately 5 × 1012 and 1 × 1010), and both are enthalpically driven processes. Reconstituting these Cu2+ sites under a range of conditions has allowed us to assign the Cu2+-binding event to the three-histidine, native, metal-binding site. Our initial efforts to characterize these Cu2+ sites have yielded data that show distinctive (and noncoupled) EPR signals associated with each copper-binding site and that this reconstituted enzyme can activate hydrogen peroxide to catalyze the oxidation of 2-aminophenol.


Metal: Cu
Ligand type: Amino acid
Anchoring strategy: Dative
Optimization: ---
Reaction: Oxidation
Max TON: ---
ee: ---
PDB: 1RZC
Notes: Oxidation of 2-aminophenol with subsequent formation of 2-aminophenoxazinone. Reaction rate = 0.09 s-1

Carbonic Anhydrase II as Host Protein for the Creation of a Biocompatible Artificial Metathesase

Ward, T.R.

Org. Biomol. Chem. 2015, 13, 5652-5655, 10.1039/c5ob00428d

We report an efficient artificial metathesase which combines an arylsulfonamide anchor within the protein scaffold human carbonic anhydrase II.


Metal: Ru
Ligand type: Carbene
Anchoring strategy: Dative
Optimization: Chemical & genetic
Reaction: Olefin metathesis
Max TON: 28
ee: ---
PDB: ---
Notes: Ring closing metathesis. 28 turnovers obtained under physiological conditions within 4 hours.

Direct Hydrogenation of Carbon Dioxide by an Artificial Reductase Obtained by Substituting Rhodium for Zinc in the Carbonic Anhydrase Catalytic Center. A Mechanistic Study

Marino, T.

ACS Catal. 2015, 5, 5397-5409, 10.1021/acscatal.5b00185

Recently, a new artificial carbonic anhydrase enzyme in which the native zinc cation has been replaced with a Rh(I) has been proposed as a new reductase that is able to efficiently catalyze the hydrogenation of olefins. In this paper, we propose the possible use of this modified enzyme in the direct hydrogenation of carbon dioxide. In our theoretical investigation, we have considered different reaction mechanisms such as reductive elimination and σ-bond metathesis. In addition, the release of the formic acid and the restoring of the catalytic cycle have also been studied. Results show that the σ-bond metathesis potential energy surface lies below the reactant species. The rate-determining step is the release of the product with an energy barrier of 12.8 kcal mol–1. On the basis of our results, we conclude that this artificial enzyme can efficiently catalyze the conversion of CO2 to HCOOH by a direct hydrogenation reaction.


Metal: Rh
Ligand type: Amino acid
Anchoring strategy: Metal substitution
Optimization: ---
Reaction: Hydrogenation
Max TON: ---
ee: ---
PDB: ---
Notes: Computational study of the reaction mechanism of the formation of HCOOH from CO2

Human Carbonic Anhydrase II as Host Protein for the Creation of Artificial Metalloenzymes: The Asymmetric Transfer Hydrogenation of Imines

Ward, T.R.

Chem. Sci. 2013, 4, 3269, 10.1039/c3sc51065d

In the presence of human carbonic anhydrase II, aryl-sulfonamide-bearing IrCp* pianostool complexes catalyze the asymmetric transfer hydrogenation of imines. Critical cofactor–protein interactions revealed by the X-ray structure of [(η5-Cp*)Ir(pico 4)Cl] 9 ⊂ WT hCA II were genetically optimized to improve the catalytic performance of the artificial metalloenzyme (68% ee, kcat/KM 6.11 × 10−3 min−1 mM−1).


Metal: Ir
Ligand type: Amino-sulfonamide; Cp*
Anchoring strategy: Supramolecular
Optimization: Chemical & genetic
Max TON: 47
ee: 70
PDB: ---
Notes: ---

Improving the Catalytic Performance of an Artificial Metalloenzyme by Computational Design

Baker, D.; Ward, T.R.

J. Am. Chem. Soc. 2015, 137, 10414-10419, 10.1021/jacs.5b06622

Artifical metalloenzymes combine the reactivity of small molecule catalysts with the selectivity of enzymes, and new methods are required to tune the catalytic properties of these systems for an application of interest. Structure-based computational design could help to identify amino acid mutations leading to improved catalytic activity and enantioselectivity. Here we describe the application of Rosetta Design for the genetic optimization of an artificial transfer hydrogenase (ATHase hereafter), [(η5-Cp*)Ir(pico)Cl] ⊂ WT hCA II (Cp* = Me5C5–), for the asymmetric reduction of a cyclic imine, the precursor of salsolsidine. Based on a crystal structure of the ATHase, computational design afforded four hCAII variants with protein backbone-stabilizing and hydrophobic cofactor-embedding mutations. In dansylamide-competition assays, these designs showed 46–64-fold improved affinity for the iridium pianostool complex [(η5-Cp*)Ir(pico)Cl]. Gratifyingly, the new designs yielded a significant improvement in both activity and enantioselectivity (from 70% ee (WT hCA II) to up to 92% ee and a 4-fold increase in total turnover number) for the production of (S)-salsolidine. Introducing additional hydrophobicity in the Cp*-moiety of the Ir-catalyst provided by adding a propyl substituent on the Cp* moiety yields the most (S)-selective (96% ee) ATHase reported to date. X-ray structural data indicate that the high enantioselectivity results from embedding the piano stool moiety within the protein, consistent with the computational model.


Metal: Ir
Ligand type: Cp*; Pyridine sulfonamide
Anchoring strategy: Supramolecular
Optimization: Genetic
Max TON: 100
ee: 96
PDB: ---
Notes: ---

Manganese-Substituted Carbonic Anhydrase as a New Peroxidase

Kazlauskas, R.J.

Chem. - Eur. J. 2006, 12, 1587-1596, 10.1002/chem.200501413

Carbonic anhydrase is a zinc metalloenzyme that catalyzes the hydration of carbon dioxide to bicarbonate. Replacing the active‐site zinc with manganese yielded manganese‐substituted carbonic anhydrase (CA[Mn]), which shows peroxidase activity with a bicarbonate‐dependent mechanism. In the presence of bicarbonate and hydrogen peroxide, (CA[Mn]) catalyzed the efficient oxidation of o‐dianisidine with kcat/KM=1.4×106 m−1 s−1, which is comparable to that for horseradish peroxidase, kcat/KM=57×106 m−1 s−1. CA[Mn] also catalyzed the moderately enantioselective epoxidation of olefins to epoxides (E=5 for p‐chlorostyrene) in the presence of an amino‐alcohol buffer, such as N,N‐bis(2‐hydroxyethyl)‐2‐aminoethanesulfonic acid (BES). This enantioselectivity is similar to that for natural heme‐based peroxidases, but has the advantage that CA[Mn] avoids the formation of aldehyde side products. CA[Mn] degrades during the epoxidation limiting the yield of the epoxidations to <12 %. Replacement of active‐site residues Asn62, His64, Asn67, Gln92, or Thr200 with alanine by site‐directed mutagenesis decreased the enantioselectivity demonstrating that the active site controls the enantioselectivity of the epoxidation.


Metal: Mn
Ligand type: Amino acid
Anchoring strategy: Metal substitution
Optimization: Chemical & genetic
Reaction: Epoxidation
Max TON: 22
ee: 67
PDB: ---
Notes: ---

Metal: Mn
Ligand type: Amino acid
Anchoring strategy: Metal substitution
Optimization: Chemical & genetic
Reaction: Epoxidation
Max TON: 9.5
ee: 55
PDB: 4CAC
Notes: PDB ID 4CAC = Structure of Zn containing hCAII

Regioselective Hydroformylation of Styrene Using Rhodium-Substituted Carbonic Anhydrase

Kazlauskas, R.J.

ChemCatChem 2010, 2, 953-957, 10.1002/cctc.201000159

CA confidential: Replacing the active‐site zinc in carbonic anhydrase (CA) by rhodium forms a new enzymatic catalyst for cofactor‐free hydroformylation of styrene with syn gas. Unlike free rhodium, this rhodium–protein hybrid, [Rh]–CA, is regioselective (8.4:1) for linear over branched aldehyde product, which is a 40‐fold change in regioselectivity compared to free rhodium.


Metal: Rh
Ligand type: Acac; Carbonyl
Anchoring strategy: Metal substitution
Optimization: Genetic
Reaction: Hydroformylation
Max TON: 298
ee: ---
PDB: 4CAC
Notes: PDB ID 4CAC = Structure of Zn containing hCAII

Stereoselective Hydrogenation of Olefins Using Rhodium-Substituted Carbonic Anhydrase—A New Reductase

Kazlauskas, R.J.

Chem. - Eur. J. 2009, 15, 1370-1376, 10.1002/chem.200801673

One useful synthetic reaction missing from nature's toolbox is the direct hydrogenation of substrates using hydrogen. Instead nature uses cofactors like NADH to reduce organic substrates, which adds complexity and cost to these reductions. To create an enzyme that can directly reduce organic substrates with hydrogen, researchers have combined metal hydrogenation catalysts with proteins. One approach is an indirect link where a ligand is linked to a protein and the metal binds to the ligand. Another approach is direct linking of the metal to protein, but nonspecific binding of the metal limits this approach. Herein, we report a direct hydrogenation of olefins catalyzed by rhodium(I) bound to carbonic anhydrase (CA‐[Rh]). We minimized nonspecific binding of rhodium by replacing histidine residues on the protein surface using site‐directed mutagenesis or by chemically modifying the histidine residues. Hydrogenation catalyzed by CA‐[Rh] is slightly slower than for uncomplexed rhodium(I), but the protein environment induces stereoselectivity favoring cis‐ over trans‐stilbene by about 20:1. This enzyme is the first cofactor‐independent reductase that reduces organic molecules using hydrogen. This catalyst is a good starting point to create variants with tailored reactivity and selectivity. This strategy to insert transition metals in the active site of metalloenzymes opens opportunities to a wider range of enzyme‐catalyzed reactions.


Metal: Rh
Ligand type: COD
Anchoring strategy: Metal substitution
Optimization: Genetic
Reaction: Hydrogenation
Max TON: 15.8
ee: ---
PDB: ---
Notes: ---

Metal: Rh
Ligand type: COD
Anchoring strategy: Metal substitution
Optimization: Genetic
Reaction: Hydrogenation
Max TON: 80.5
ee: ---
PDB: 4CAC
Notes: PDB ID 4CAC = Structure of Zn containing hCAII

Transforming Carbonic Anhydrase into Epoxide Synthase by Metal Exchange

Soumillion, P.

ChemBioChem 2006, 7, 1013-1016, 10.1002/cbic.200600127

Enantioselective epoxidation of styrene was observed in the presence of manganese‐containing carbonic anhydrase as catalyst. The probable oxygen‐transfer reagent is peroxymonocarbonate, which has a structural similarity with the hydrogenocarbonate substrate of the natural reaction. Styrene was chosen as the enzyme possesses a small hydrophobic cavity close to the active site.


Metal: Mn
Ligand type: Amino acid
Anchoring strategy: Metal substitution
Optimization: Chemical & genetic
Reaction: Epoxidation
Max TON: 4.1
ee: 52
PDB: ---
Notes: ---

Metal: Mn
Ligand type: Amino acid
Anchoring strategy: Metal substitution
Optimization: Chemical & genetic
Reaction: Epoxidation
Max TON: 10.3
ee: 40
PDB: ---
Notes: ---