20 publications

20 publications

A Hydrogenase Model System Based on the Sequence of Cytochrome c: Photochemical Hydrogen Evolution in Aqueous Media

Hayashi, T

Chem. Commun. 2011, 47, 8229, 10.1039/c1cc11157d

The diiron carbonyl cluster is held by a native CXXC motif, which includes Cys14 and Cys17, in the cytochrome c sequence. It is found that the diiron carbonyl complex works well as a catalyst for H2 evolution. It has a TON of ∼80 over 2 h at pH 4.7 in the presence of a Ru-photosensitizer and ascorbate as a sacrificial reagent in aqueous media.


Metal: Fe
Ligand type: Carbonyl
Host protein: Cytochrome c
Anchoring strategy: Dative
Optimization: ---
Reaction: H2 evolution
Max TON: 82
ee: ---
PDB: ---
Notes: Horse heart cytochrome C

An Artificial Metalloenzyme for Olefin Metathesis

Hilvert, D.; Ward, T.R.

Chem. Commun. 2011, 47, 12068, 10.1039/c1cc15005g

A Grubbs–Hoveyda type olefin metathesis catalyst, equipped with an electrophilic bromoacetamide group, was used to modify a cysteine-containing variant of a small heat shock protein from Methanocaldococcus jannaschii. The resulting artificial metalloenzyme was found to be active under acidic conditions in a benchmark ring closing metathesis reaction.


Metal: Ru
Ligand type: Carbene
Anchoring strategy: Covalent
Optimization: ---
Reaction: Olefin metathesis
Max TON: 25
ee: ---
PDB: ---
Notes: RCM

Artificial Metalloenzymes Based on the Biotin-Avidin Technology: Enantioselective Catalysis and Beyond

Review

Ward, T.R.

Acc. Chem. Res. 2011, 44, 47-57, 10.1021/ar100099u

Artificial metalloenzymes are created by incorporating an organometallic catalyst within a host protein. The resulting hybrid can thus provide access to the best features of two distinct, and often complementary, systems: homogeneous and enzymatic catalysts. The coenzyme may be positioned with covalent, dative, or supramolecular anchoring strategies. Although initial reports date to the late 1970s, artificial metalloenzymes for enantioselective catalysis have gained significant momentum only in the past decade, with the aim of complementing homogeneous, enzymatic, heterogeneous, and organic catalysts. Inspired by a visionary report by Wilson and Whitesides in 1978, we have exploited the potential of biotin−avidin technology in creating artificial metalloenzymes. Owing to the remarkable affinity of biotin for either avidin or streptavidin, covalent linking of a biotin anchor to a catalyst precursor ensures that, upon stoichiometric addition of (strept)avidin, the metal moiety is quantitatively incorporated within the host protein. In this Account, we review our progress in preparing and optimizing these artificial metalloenzymes, beginning with catalytic hydrogenation as a model and expanding from there. These artificial metalloenzymes can be optimized by both chemical (variation of the biotin−spacer−ligand moiety) and genetic (mutation of avidin or streptavidin) means. Such chemogenetic optimization schemes were applied to various enantioselective transformations. The reactions implemented thus far include the following: (i) The rhodium-diphosphine catalyzed hydrogenation of N-protected dehydroaminoacids (ee up to 95%); (ii) the palladium-diphosphine catalyzed allylic alkylation of 1,3-diphenylallylacetate (ee up to 95%); (iii) the ruthenium pianostool-catalyzed transfer hydrogenation of prochiral ketones (ee up to 97% for aryl-alkyl ketones and ee up to 90% for dialkyl ketones); (iv) the vanadyl-catalyzed oxidation of prochiral sulfides (ee up to 93%). A number of noteworthy features are reminiscent of homogeneous catalysis, including straightforward access to both enantiomers of the product, the broad substrate scope, organic solvent tolerance, and an accessible range of reactions that are typical of homogeneous catalysts. Enzyme-like features include access to genetic optimization, an aqueous medium as the preferred solvent, Michaelis−Menten behavior, and single-substrate derivatization. The X-ray characterization of artificial metalloenzymes provides fascinating insight into possible enantioselection mechanisms involving a well-defined second coordination sphere environment. Thus, such artificial metalloenzymes combine attractive features of both homogeneous and enzymatic kingdoms. In the spirit of surface borrowing, that is, modulating ligand affinity by harnessing existing protein surfaces, this strategy can be extended to selectively binding streptavidin-incorporated biotinylated ruthenium pianostool complexes to telomeric DNA. This application paves the way for chemical biology applications of artificial metalloenzymes.


Notes: ---

Artificial Metalloenzymes for Olefin Metathesis Based on the Biotin-(Strept)Avidin Technology

Ward, T.R.

Chem. Commun. 2011, 47, 12065, 10.1039/c1cc15004a

Incorporation of a biotinylated Hoveyda-Grubbs catalyst within (strept)avidin affords artificial metalloenzymes for the ring-closing metathesis of N-tosyl diallylamine in aqueous solution. Optimization of the performance can be achieved either by chemical or genetic means.


Metal: Ru
Ligand type: Carbene
Host protein: Streptavidin (Sav)
Anchoring strategy: Supramolecular
Optimization: Chemical
Reaction: Olefin metathesis
Max TON: 14
ee: ---
PDB: ---
Notes: RCM

Metal: Ru
Ligand type: Carbene
Host protein: Avidin (Av)
Anchoring strategy: Supramolecular
Optimization: Chemical
Reaction: Olefin metathesis
Max TON: 19
ee: ---
PDB: ---
Notes: RCM

Artificial Transfer Hydrogenases for the Enantioselective Reduction of Cyclic Imines

Ward, T.R.

Angew. Chem. Int. Ed. 2011, 50, 3026-3029, 10.1002/anie.201007820

Man‐made activity: Introduction of a biotinylated iridium piano stool complex within streptavidin affords an artificial imine reductase (see scheme). Saturation mutagenesis allowed optimization of the activity and the enantioselectivity of this metalloenzyme, and its X‐ray structure suggests that a nearby lysine residue acts as a proton source during the transfer hydrogenation.


Metal: Ir
Ligand type: Amino-sulfonamide; Cp*
Host protein: Streptavidin (Sav)
Anchoring strategy: Supramolecular
Optimization: Chemical & genetic
Max TON: 4000
ee: 96
PDB: 3PK2
Notes: ---

Metal: Rh
Ligand type: Amino-sulfonamide; Cp*
Host protein: Streptavidin (Sav)
Anchoring strategy: Supramolecular
Optimization: Chemical & genetic
Max TON: 94
ee: 52
PDB: 3PK2
Notes: ---

Metal: Ru
Ligand type: Amino-sulfonamide; P-cymene
Host protein: Streptavidin (Sav)
Anchoring strategy: Supramolecular
Optimization: Chemical & genetic
Max TON: 97
ee: 22
PDB: 3PK2
Notes: ---

Metal: Ru
Ligand type: Amino-sulfonamide; Benzene
Host protein: Streptavidin (Sav)
Anchoring strategy: Supramolecular
Optimization: Chemical & genetic
Max TON: 76
ee: 12
PDB: 3PK2
Notes: ---

Bimetallic Copper-Heme-Protein-DNA Hybrid Catalyst for Diels Alder Reaction

Fruk, L.; Niemeyer, C.M.

Croat. Chem. Acta 2011, 84, 269-275, 10.5562/cca1828

A bimetallic heme-DNA cofactor, containing an iron and a copper center, was synthesized for the design of novel hybrid catalysts for stereoselective synthesis. The cofactor was used for the reconstitution of apo-myoglobin. Both the cofactor alone and its myoglobin adduct were used to catalyze a model Diels Alder reaction. Stereoselectivity of this conversion was analyzed by chiral HPLC. Reactions carried out in the presence of myoglobin-heme-Cu-DNA catalyst showed greater product conversion and stereoselectivity than those carried out with the heme-Cu-DNA cofactor. This observation suggested that the protein shell plays a significant role in the catalytic conversion.


Metal: Cu
Ligand type: Bipyridine
Host protein: Myoglobin (Mb)
Anchoring strategy: Supramolecular
Optimization: ---
Max TON: 7.1
ee: 18
PDB: ---
Notes: Horse heart myoglobin

Bioinspired Catalyst Design and Artificial Metalloenzymes

Review

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

Chem. - Eur. J. 2011, 17, 4680-4698, 10.1002/chem.201003646

Many bioinspired transition‐metal catalysts have been developed over the recent years. In this review the progress in the design and application of ligand systems based on peptides and DNA and the development of artificial metalloenzymes are reviewed with a particular emphasis on the combination of phosphane ligands with powerful molecular recognition and shape selectivity of biomolecules. The various approaches for the assembly of these catalytic systems will be highlighted, and the possibilities that the use of the building blocks of Nature provide for catalyst optimisation strategies are discussed.


Notes: ---

Burkavidin: A Novel Secreted Biotin-Binding Protein from the Human Pathogen Burkholderia Pseudomallei

Creus, M.

Protein Expression Purif. 2011, 77, 131-139, 10.1016/j.pep.2011.01.003

The avidin–biotin technology has many applications, including molecular detection; immobilization; protein purification; construction of supramolecular assemblies and artificial metalloenzymes. Here we present the recombinant expression of novel biotin-binding proteins from bacteria and the purification and characterization of a secreted burkavidin from the human pathogen Burkholderia pseudomallei. Expression of the native burkavidin in Escherichia coli led to periplasmic secretion and formation of a biotin-binding, thermostable, tetrameric protein containing an intra-monomeric disulphide bond. Burkavidin showed one main species as measured by isoelectric focusing, with lower isoelectric point (pI) than streptavidin. To exemplify the potential use of burkavidin in biotechnology, an artificial metalloenzyme was generated using this novel protein-scaffold and shown to exhibit enantioselectivity in a rhodium-catalysed hydrogenation reaction.


Metal: Rh
Ligand type: Diphenylphosphine
Host protein: Burkavidin
Anchoring strategy: Supramolecular
Optimization: Chemical & genetic
Reaction: Hydrogenation
Max TON: ~110
ee: 65
PDB: ---
Notes: ---

Chemically Engineered Papain as Artificial Formate Dehydrogenase for NAD(P)H Regeneration

Salmain, M.

Org. Biomol. Chem. 2011, 9, 5720, 10.1039/c1ob05482a

Organometallic complexes of the general formula [(η6-arene)Ru(N⁁N)Cl]+ and [(η5-Cp*)Rh(N⁁N)Cl]+ where N⁁N is a 2,2′-dipyridylamine (DPA) derivative carrying a thiol-targeted maleimide group, 2,2′-bispyridyl (bpy), 1,10-phenanthroline (phen) or ethylenediamine (en) and arene is benzene, 2-chloro-N-[2-(phenyl)ethyl]acetamide or p-cymene were identified as catalysts for the stereoselective reduction of the enzyme cofactors NAD(P)+ into NAD(P)H with formate as a hydride donor. A thorough comparison of their effectiveness towards NAD+ (expressed as TOF) revealed that the RhIII complexes were much more potent catalysts than the RuII complexes. Within the RuII complex series, both the N⁁N and arene ligands forming the coordination sphere had a noticeable influence on the activity of the complexes. Covalent anchoring of the maleimide-functionalized RuII and RhIII complexes to the cysteine endoproteinase papain yielded hybrid metalloproteins, some of them displaying formate dehydrogenase activity with potentially interesting kinetic parameters.


Metal: Rh
Ligand type: Cp*; Poly-pyridine
Host protein: Papain (PAP)
Anchoring strategy: Covalent
Optimization: Chemical
Reaction: Hydrogenation
Max TON: ---
ee: ---
PDB: ---
Notes: TOF = 52.1 h-1 for NAD+

Covalent Anchoring of a Racemization Catalyst to CALB-Beads: Towards Dual Immobilization of DKR Catalysts

Klein Gebbink, R.J.M.; van Koten, G.

Tetrahedron Lett. 2011, 52, 1601-1604, 10.1016/j.tetlet.2011.01.106

The preparation of a heterogeneous bifunctional catalytic system, combining the catalytic properties of an organometallic catalyst (racemization) with those of an enzyme (enantioselective acylation) is described. A novel ruthenium phosphonate inhibitor was synthesized and covalently anchored to a lipase immobilized on a solid support (CALB, Novozym® 435). The immobilized bifunctional catalytic system showed activity in both racemization of (S)-1-phenylethanol and selective acylation of 1-phenylethanol.


Metal: Ru
Anchoring strategy: Covalent
Optimization: Chemical
Reaction: Acylation
Max TON: ---
ee: >99%
PDB: ---
Notes: Lipase CALB is immobilized on a solid support (Novozym®435). Dynamic kinetic resolution (DKR) of 1-phenylethanol to the acylated product.

Covalent Versus Non-covalent (Biocatalytic) Approaches for Enantioselective Sulfoxidation Catalyzed by Corrole Metal Complexes

Gross, Z.

Cat. Sci. Technol. 2011, 1, 578, 10.1039/c1cy00046b

Oxidation of thioanisoles, catalyzed by chiral manganese(III) and iron(III) corroles, provides the corresponding sulfoxides in moderate chemical yields and low enantioselectivities. Biocatalysis by non-chiral albumin-associated manganese(III) corroles proceeds much better and allows for the enantioselective synthesis of the pharmacologically important R-modafinil, in 88% yield and 73% ee.


Metal: Mn
Ligand type: Corrole
Anchoring strategy: Supramolecular
Optimization: Chemical & genetic
Reaction: Sulfoxidation
Max TON: 45
ee: 70
PDB: ---
Notes: ---

Definite Coordination Arrangement of Organometallic Palladium Complexes Accumulated on the Designed Interior Surface of Apo-Ferritin

Ueno, T.

Chem. Commun. 2011, 47, 170-172, 10.1039/C0CC02221G

Apo-ferritin (apo-Fr) mutants are used as scaffolds to accommodate palladium (allyl) complexes. Various coordination arrangements of the Pd complexes are achieved by adjusting the positions of cysteine and histidine residues on the interior surface of the apo-Fr cage.


Metal: Pd
Ligand type: Allyl
Host protein: Ferritin
Anchoring strategy: Dative
Optimization: Genetic
Reaction: Suzuki coupling
Max TON: ---
ee: ---
PDB: ---
Notes: ---

Design and Evolution of Artificial Metalloenzymes: Biomimetic Aspects

Review

Creus, M.; Ward, T.R.

Prog. Inorg. Chem. 2011, 203-253, 10.1002/9781118148235.ch4

n/a


Notes: ---

Design of a Switchable Eliminase

DeGrado, W.F.

Proc. Natl. Acad. Sci. U. S. A. 2011, 108, 6823-6827, 10.1073/pnas.1018191108

The active sites of enzymes are lined with side chains whose dynamic, geometric, and chemical properties have been finely tuned relative to the corresponding residues in water. For example, the carboxylates of glutamate and aspartate are weakly basic in water but become strongly basic when dehydrated in enzymatic sites. The dehydration of the carboxylate, although intrinsically thermodynamically unfavorable, is achieved by harnessing the free energy of folding and substrate binding to reach the required basicity. Allosterically regulated enzymes additionally rely on the free energy of ligand binding to stabilize the protein in a catalytically competent state. We demonstrate the interplay of protein folding energetics and functional group tuning to convert calmodulin (CaM), a regulatory binding protein, into AlleyCat, an allosterically controlled eliminase. Upon binding Ca(II), native CaM opens a hydrophobic pocket on each of its domains. We computationally identified a mutant that (i) accommodates carboxylate as a general base within these pockets, (ii) interacts productively in the Michaelis complex with the substrate, and (iii) stabilizes the transition state for the reaction. Remarkably, a single mutation of an apolar residue at the bottom of an otherwise hydrophobic cavity confers catalytic activity on calmodulin. AlleyCat showed the expected pH-rate profile, and it was inactivated by mutation of its active site Glu to Gln. A variety of control mutants demonstrated the specificity of the design. The activity of this minimal 75-residue allosterically regulated catalyst is similar to that obtained using more elaborate computational approaches to redesign complex enzymes to catalyze the Kemp elimination reaction.


Metal: Ca
Ligand type: Amino acid
Anchoring strategy: Dative
Optimization: Genetic
Reaction: Kemp elimination
Max TON: >40
ee: ---
PDB: 2KZ2
Notes: Ca acts as allosteric regulator, catalytically active site contains no metal

Dual Modification of a Triple-Stranded β-Helix Nanotube with Ru and Re Metal Complexes to Promote Photocatalytic Reduction of CO2

Ueno, T.

Chem. Commun. 2011, 47, 2074, 10.1039/C0CC03015E

We have constructed a robust β-helical nanotube from the component proteins of bacteriophage T4 and modified this nanotube with RuII(bpy)3 and ReI(bpy)(CO)3Cl complexes. The photocatalytic system arranged on the tube catalyzes the reduction of CO2 with higher reactivity than that of the mixture of the monomeric forms.


Metal: Re
Ligand type: Bipyridine; CO
Host protein: [(gp5βf)3]2
Anchoring strategy: Cystein-maleimide
Optimization: ---
Reaction: CO2 reduction
Max TON: ---
ee: ---
PDB: ---
Notes: ---

Metal: Ru
Ligand type: Bipyridine
Host protein: [(gp5βf)3]2
Anchoring strategy: Lysine-succinimide
Optimization: Genetic
Reaction: CO2 reduction
Max TON: ---
ee: ---
PDB: ---
Notes: ---

Merging the Best of Two Worlds: Artificial Metalloenzymes for Enantioselective Catalysis

Review

Ward, T.R.

Chem. Commun. 2011, 47, 8470, 10.1039/c1cc11592h

Artificial metalloenzymes result from combining a catalytically active organometallic moiety with a macromolecular host. The resulting hybrid catalysts combine attractive features of both homogeneous and enzymatic systems. Herein we summarize the recent progress in this emerging field and outline the challenges ahead.


Notes: ---

Nature-Driven Photochemistry for Catalytic Solar Hydrogen Production: A Photosystem I-Transition Metal Catalyst Hybrid

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

J. Am. Chem. Soc. 2011, 133, 16334-16337, 10.1021/ja206012r

Solar energy conversion of water into the environmentally clean fuel hydrogen offers one of the best long-term solutions for meeting future energy demands. Nature provides highly evolved, finely tuned molecular machinery for solar energy conversion that exquisitely manages photon capture and conversion processes to drive oxygenic water-splitting and carbon fixation. Herein, we use one of Nature’s specialized energy-converters, the Photosystem I (PSI) protein, to drive hydrogen production from a synthetic molecular catalyst comprised of inexpensive, earth-abundant materials. PSI and a cobaloxime catalyst self-assemble, and the resultant complex rapidly produces hydrogen in aqueous solution upon exposure to visible light. This work establishes a strategy for enhancing photosynthetic efficiency for solar fuel production by augmenting natural photosynthetic systems with synthetically tunable abiotic catalysts.


Metal: Co
Ligand type: Oxime; Pyridine
Host protein: Photosystem I (PSI)
Anchoring strategy: Undefined
Optimization: ---
Reaction: H2 evolution
Max TON: 2080
ee: ---
PDB: ---
Notes: Recalculated TON

OsO4·Streptavidin: A Tunable Hybrid Catalyst for the Enantioselective cis-Dihydroxylation of 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.


Metal: Os
Ligand type: Undefined
Host protein: Streptavidin (Sav)
Anchoring strategy: Supramolecular
Optimization: Genetic
Reaction: Dihydroxylation
Max TON: 16
ee: 97
PDB: ---
Notes: ---

Precise Design of Artificial Cofactors for Enhancing Peroxidase Activity of Myoglobin: Myoglobin Mutant H64D Reconstituted with a “Single-Winged Cofactor” is Equivalent to Native Horseradish Peroxidase in Oxidation Activity

Matsuo, T.

Chem. - Asian J. 2011, 6, 2491-2499, 10.1002/asia.201100107

H64D myoglobin mutant was reconstituted with two different types of synthetic hemes that have aromatic rings and a carboxylate‐based cluster attached to the terminus of one or both of the heme‐propionate moieties, thereby forming a “single‐winged cofactor” and “double‐winged cofactor,” respectively. The reconstituted mutant myoglobins have smaller Km values with respect to 2‐methoxyphenol oxidation activity relative to the parent mutant with native heme. This suggests that the attached moiety functions as a substrate‐binding domain. However, the kcat value of the mutant myoglobin with the double‐winged cofactor is much lower than that of the mutant with the native heme. In contrast, the mutant reconstituted with the single‐winged cofactor has a larger kcat value, thereby resulting in overall catalytic activity that is essentially equivalent to that of the native horseradish peroxidase. Enhanced peroxygenase activity was also observed for the mutant myoglobin with the single‐winged cofactor, thus indicating that introduction of an artificial substrate‐binding domain at only one of the heme propionates in the H64D mutant is the optimal engineering strategy for improving the peroxidase activity of myoglobin.


Metal: Fe
Host protein: Myoglobin (Mb)
Anchoring strategy: Reconstitution
Optimization: Chemical & genetic
Max TON: ---
ee: ---
PDB: ---
Notes: ---

The Important Role of Covalent Anchor Positions in Tuning Catalytic Properties of a Rationally Designed MnSalen-Containing Metalloenzyme

Lu, Y.; Zhang, J.-L.

ACS Catal. 2011, 1, 1083-1089, 10.1021/cs200258e

Two questions important to the success in metalloenzyme design are how to attach or anchor metal cofactors inside protein scaffolds and in what way such positioning affects enzymatic properties. We have previously reported a dual anchoring method to position a nonnative cofactor, MnSalen (1), inside the heme cavity of apo sperm whale myoglobin (Mb) and showed that the dual anchoring can increase both the activity and enantioselectivity over single anchoring methods, making this artificial enzyme an ideal system to address the above questions. Here, we report systematic investigations of the effect of different covalent attachment or anchoring positions on reactivity and selectivity of sulfoxidation by the MnSalen-containing Mb enzymes. We have found that changing the left anchor from Y103C to T39C has an almost identical effect of increasing rate by 1.8-fold and increasing selectivity by +15% for S, whether the right anchor is L72C or S108C. At the same time, regardless of the identity of the left anchor, changing the right anchor from S108C to L72C increases the rate by 4-fold and selectivity by +66%. The right anchor site was observed to have a greater influence than the left anchor site on the reactivity and selectivity in sulfoxidation of a wide scope of other ortho-, meta- and para-substituted substrates. The 1·Mb(T39C/L72C) showed the highest reactivity (TON up to 2.32 min–1) and selectivity (ee % up to 83%) among the different anchoring positions examined. Molecular dynamic simulations indicate that these changes in reactivity and selectivity may be due to the steric effects of the linker arms inside the protein cavity. These results indicate that small differences in the anchor positions can result in significant changes in reactivity and enantioselectivity, probably through steric interactions with substrates when they enter the substrate-binding pocket, and that the effects of right and left anchor positions are independent and additive in nature. The finding that the anchoring arms can influence both the positioning of the cofactor and steric control of substrate entrance will help design better functional metalloenzymes with predicted catalytic activity and selectivity.


Metal: Mn
Ligand type: Salen
Host protein: Myoglobin (Mb)
Anchoring strategy: Covalent
Optimization: Genetic
Reaction: Sulfoxidation
Max TON: ---
ee: 83
PDB: ---
Notes: Reaction rate: 2.3 min-1