8-Amino-5,6,7,8-tetrahydroquinoline in Iridium(III) Biotinylated Cp* Complex as Artificial Imine Reductase
New J. Chem. 2018, 42, 18773-18776, 10.1039/C8NJ04558E
The imine reductase formed by the (R)-CAMPY ligand bound to the S112M Sav mutant showed an 83% ee in the asymmetric transfer hydrogenation of 6,7-dimethoxy-1-methyl-3,4-dihydroisoquinoline.
Max TON: 32ee: 83PDB: ---Notes: ---
Max TON: 99ee: 13PDB: ---Notes: ---
Abiotic reduction of ketones with silanes catalysed by carbonic anhydrase through an enzymatic zinc hydride
Nat. Chem. 2021, 13, 312-318, 10.1038/s41557-020-00633-7
Enzymatic reactions through mononuclear metal hydrides are unknown in nature, despite the prevalence of such intermediates in the reactions of synthetic transition-metal catalysts. If metalloenzymes could react through abiotic intermediates like these, then the scope of enzyme-catalysed reactions would expand. Here we show that zinc-containing carbonic anhydrase enzymes catalyse hydride transfers from silanes to ketones with high enantioselectivity. We report mechanistic data providing strong evidence that the process involves a mononuclear zinc hydride. This work shows that abiotic silanes can act as reducing equivalents in an enzyme-catalysed process and that monomeric hydrides of electropositive metals, which are typically unstable in protic environments, can be catalytic intermediates in enzymatic processes. Overall, this work bridges a gap between the types of transformation in molecular catalysis and biocatalysis.
Metal: ZnLigand type: Histidine residuesAnchoring strategy: NativeOptimization: ChemicalMax TON: 500ee: >99PDB: ---Notes: ---
A Dual Anchoring Strategy for the Localization and Activation of Artificial Metalloenzymes Based on the Biotin−Streptavidin Technology
J. Am. Chem. Soc. 2013, 135, 5384-5388, 10.1021/ja309974s
Artificial metalloenzymes result from anchoring an active catalyst within a protein environment. Toward this goal, various localization strategies have been pursued: covalent, supramolecular, or dative anchoring. Herein we show that introduction of a suitably positioned histidine residue contributes to firmly anchor, via a dative bond, a biotinylated rhodium piano stool complex within streptavidin. The in silico design of the artificial metalloenzyme was confirmed by X-ray crystallography. The resulting artificial metalloenzyme displays significantly improved catalytic performance, both in terms of activity and selectivity in the transfer hydrogenation of imines. Depending on the position of the histidine residue, both enantiomers of the salsolidine product can be obtained.
Max TON: 14ee: 11PDB: ---Notes: ---
Max TON: 100ee: 79PDB: ---Notes: ---
Alternative Strategy to Obtain Artificial Imine Reductase by Exploiting Vancomycin/D-Ala-D-Ala Interactions with an Iridium Metal Complex
Inorg. Chem. 2021, 60, 2976-2982, 10.1021/acs.inorgchem.0c02969
Based on the supramolecular interaction between vancomycin (Van), an antibiotic glycopeptide, and D-Ala-D-Ala (DADA) dipeptides, a novel class of artificial metalloenzymes was synthesized and characterized. The presence of an iridium(III) ligand at the N-terminus of DADA allowed the use of the metalloenzyme as a catalyst in the asymmetric transfer hydrogenation of cyclic imines. In particular, the type of link between DADA and the metal-chelating moiety was found to be fundamental for inducing asymmetry in the reaction outcome, as highlighted by both computational studies and catalytic results. Using the [IrCp*(m-I)Cl]Cl ⊂ Van complex in 0.1 M CH3COONa buffer at pH 5, a significant 70% (S) e.e. was obtained in the reduction of quinaldine B.
Host protein: DADA dipeptideOptimization: ChemicalMax TON: 50ee: 70PDB: ---Notes: ---
An Artificial Imine Reductase Based on the Ribonuclease S Scaffold
ChemCatChem 2014, 6, 736-740, 10.1002/cctc.201300995
Dative anchoring of a piano‐stool complex within ribonuclease S resulted in an artificial imine reductase. The catalytic performance was modulated upon variation of the coordinating amino acid residues in the S‐peptide. Binding of Cp*Ir (Cp*=C5Me5) to the native active site resulted in good conversions and moderate enantiomeric excess values for the synthesis of salsolidine.
Host protein: Ribonuclease SMax TON: 4ee: 18PDB: ---Notes: ---
An NAD(P)H-Dependent Artificial Transfer Hydrogenase for Multienzymatic Cascades
J. Am. Chem. Soc. 2016, 138, 5781-5784, 10.1021/jacs.6b02470
Enzymes typically depend on either NAD(P)H or FADH2 as hydride source for reduction purposes. In contrast, organometallic catalysts most often rely on isopropanol or formate to generate the reactive hydride moiety. Here we show that incorporation of a Cp*Ir cofactor possessing a biotin moiety and 4,7-dihydroxy-1,10-phenanthroline into streptavidin yields an NAD(P)H-dependent artificial transfer hydrogenase (ATHase). This ATHase (0.1 mol%) catalyzes imine reduction with 1 mM NADPH (2 mol%), which can be concurrently regenerated by a glucose dehydrogenase (GDH) using only 1.2 equiv of glucose. A four-enzyme cascade consisting of the ATHase, the GDH, a monoamine oxidase, and a catalase leads to the production of enantiopure amines.
Max TON: >999ee: >99PDB: ---Notes: ---
Artificial Iron Hydrogenase Made by Covalent Grafting of Knölker's Complex into Xylanase: Application in Asymmetric Hydrogenation of an Aryl Ketone in Water
Biotechnol. Appl. Biochem. 2020, 67, 563-573, 10.1002/bab.1906
We report a new artificial hydrogenase made by covalent anchoring of the iron Knölker's complex to a xylanase S212C variant. This artificial metalloenzyme was found to be able to catalyze efficiently the transfer hydrogenation of the benchmark substrate trifluoroacetophenone by sodium formate in water, yielding the corresponding secondary alcohol as a racemic. The reaction proceeded more than threefold faster with the XlnS212CK biohybrid than with the Knölker's complex alone. In addition, efficient conversion of trifluoroacetophenone to its corresponding alcohol was reached within 60 H with XlnS212CK, whereas a ≈2.5-fold lower conversion was observed with Knölker's complex alone as catalyst. Moreover, the data were rationalized with a computational strategy suggesting the key factors of the selectivity. These results suggested that the Knölker's complex was most likely flexible and could experience free rotational reorientation within the active-site pocket of Xln A, allowing it to access the subsite pocket populated by trifluoroacetophenone.
Metal: FeLigand type: CyclopentadienylHost protein: Xylanase A (XynA)Anchoring strategy: CovalentOptimization: ---Max TON: 9ee: ---PDB: ---Notes: ---
Artificial Metalloenzymes Based on Biotin-Avidin Technology for the Enantioselective Reduction of Ketones by Transfer Hydrogenation
Proc. Natl. Acad. Sci. U. S. A. 2005, 102, 4683-4687, 10.1073/pnas.0409684102
Most physiological and biotechnological processes rely on molecular recognition between chiral (handed) molecules. Manmade homogeneous catalysts and enzymes offer complementary means for producing enantiopure (single-handed) compounds. As the subtle details that govern chiral discrimination are difficult to predict, improving the performance of such catalysts often relies on trial-and-error procedures. Homogeneous catalysts are optimized by chemical modification of the chiral environment around the metal center. Enzymes can be improved by modification of gene encoding the protein. Incorporation of a biotinylated organometallic catalyst into a host protein (avidin or streptavidin) affords versatile artificial metalloenzymes for the reduction of ketones by transfer hydrogenation. The boric acid·formate mixture was identified as a hydrogen source compatible with these artificial metalloenzymes. A combined chemo-genetic procedure allows us to optimize the activity and selectivity of these hybrid catalysts: up to 94% (R) enantiomeric excess for the reduction of p-methylacetophenone. These artificial metalloenzymes display features reminiscent of both homogeneous catalysts and enzymes.
Max TON: 92ee: 94PDB: ---Notes: ---
Max TON: 30ee: 63PDB: ---Notes: ---
Artificial Metalloenzymes for the Diastereoselective Reduction of NAD+ to NAD2H
Org. Biomol. Chem. 2015, 13, 357-360, 10.1039/c4ob02071e
Stereoselectively labelled isotopomers of NAD(P)H are highly relevant for mechanistic studies of enzymes which utilize them as redox equivalents.
Optimization: ---Notes: ---
Artificial Transfer Hydrogenases Based on the Biotin-(Strept)avidin Technology: Fine Tuning the Selectivity by Saturation Mutagenesis of the Host Protein
J. Am. Chem. Soc. 2006, 128, 8320-8328, 10.1021/ja061580o
Incorporation of biotinylated racemic three-legged d6-piano stool complexes in streptavidin yields enantioselective transfer hydrogenation artificial metalloenzymes for the reduction of ketones. Having identified the most promising organometallic catalyst precursors in the presence of wild-type streptavidin, fine-tuning of the selectivity is achieved by saturation mutagenesis at position S112. This choice for the genetic optimization site is suggested by docking studies which reveal that this position lies closest to the biotinylated metal upon incorporation into streptavidin. For aromatic ketones, the reaction proceeds smoothly to afford the corresponding enantioenriched alcohols in up to 97% ee (R) or 70% (S). On the basis of these results, we suggest that the enantioselection is mostly dictated by CH/π interactions between the substrate and the η6-bound arene. However, these enantiodiscriminating interactions can be outweighed in the presence of cationic residues at position S112 to afford the opposite enantiomers of the product.
Max TON: 96ee: 80PDB: ---Notes: ---
Max TON: 73ee: 60PDB: ---Notes: ---
Max TON: 95ee: 70PDB: ---Notes: ---
Max TON: 79ee: 97PDB: ---Notes: ---
Artificial Transfer Hydrogenases for the Enantioselective Reduction of Cyclic Imines
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.
Max TON: 4000ee: 96Notes: ---
Max TON: 94ee: 52Notes: ---
Max TON: 97ee: 22Notes: ---
Max TON: 76ee: 12Notes: ---
Breaking Symmetry: Engineering Single-Chain Dimeric Streptavidin as Host for Artificial Metalloenzymes
J. Am. Chem. Soc. 2019, 141, 15869-15878, 10.1021/jacs.9b06923
The biotin–streptavidin technology has been extensively exploited to engineer artificial metalloenzymes (ArMs) that catalyze a dozen different reactions. Despite its versatility, the homotetrameric nature of streptavidin (Sav) and the noncooperative binding of biotinylated cofactors impose two limitations on the genetic optimization of ArMs: (i) point mutations are reflected in all four subunits of Sav, and (ii) the noncooperative binding of biotinylated cofactors to Sav may lead to an erosion in the catalytic performance, depending on the cofactor:biotin-binding site ratio. To address these challenges, we report on our efforts to engineer a (monovalent) single-chain dimeric streptavidin (scdSav) as scaffold for Sav-based ArMs. The versatility of scdSav as host protein is highlighted for the asymmetric transfer hydrogenation of prochiral imines using [Cp*Ir(biot-p-L)Cl] as cofactor. By capitalizing on a more precise genetic fine-tuning of the biotin-binding vestibule, unrivaled levels of activity and selectivity were achieved for the reduction of challenging prochiral imines. Comparison of the saturation kinetic data and X-ray structures of [Cp*Ir(biot-p-L)Cl]·scdSav with a structurally related [Cp*Ir(biot-p-L)Cl]·monovalent scdSav highlights the advantages of the presence of a single biotinylated cofactor precisely localized within the biotin-binding vestibule of the monovalent scdSav. The practicality of scdSav-based ArMs was illustrated for the reduction of the salsolidine precursor (500 mM) to afford (R)-salsolidine in 90% ee and >17 000 TONs. Monovalent scdSav thus provides a versatile scaffold to evolve more efficient ArMs for in vivo catalysis and large-scale applications.
Max TON: 17000ee: 98PDB: 6S4QNotes: Additional PDB: 6S50
Chimeric Streptavidins as Host Proteins for Artificial Metalloenzymes
ACS Catal. 2018, 8, 1476-1484, 10.1021/acscatal.7b03773
The streptavidin scaffold was expanded with well-structured naturally occurring motifs. These chimeric scaffolds were tested as hosts for biotinylated catalysts as artificial metalloenzymes (ArM) for asymmetric transfer hydrogenation, ring-closing metathesis and anion−π catalysis. The additional second coordination sphere elements significantly influence both the activity and the selectivity of the resulting hybrid catalysts. These findings lead to the identification of propitious chimeric streptavidins for future directed evolution efforts of artificial metalloenzymes.
Max TON: 970ee: 13PDB: ---Notes: ---
Max TON: 158ee: 82PDB: ---Notes: ---
Ligand type: CarbeneReaction: Olefin metathesisMax TON: 105ee: ---PDB: ---Notes: RCM, biotinylated Hoveyda-Grubbs second generation catalyst
Metal: ---Ligand type: Biotinylated naphthalenediimidReaction: Anion-π catalysisMax TON: 6ee: 41PDB: ---Notes: No metal
Computational Insights on an Artificial Imine Reductase Based on the Biotin-Streptavidin Technology
ACS Catal. 2014, 4, 833-842, 10.1021/cs400921n
We present a computational study that combines protein–ligand docking, quantum mechanical, and quantum mechanical/molecular mechanical calculations to scrutinize the mechanistic behavior of the first artificial enzyme able to enantioselectively reduce cyclic imines. We applied a novel strategy that allows the characterization of transition state structures in the protein host and their associated reaction paths. Of the most striking results of our investigation is the identification of major conformational differences between the transition state geometries of the lowest energy paths leading to (R)- and (S)-reduction products. The molecular features of (R)- and (S)-transition states highlight distinctive patterns of hydrophobic and polar complementarities between the substrate and the binding site. These differences lead to an activation energy gap that stands in very good agreement with the experimentally determined enantioselectivity. This study sheds light on the mechanism by which transfer hydrogenases operate and illustrates how the change of environment (from homogeneous solution conditions to the asymmetric protein frame) affect the reactivity of the organometallic cofactor. It provides novel insights on the complexity in integrating unnatural organometallic compounds into biological scaffolds. The modeling strategy that we pursued, based on the generation of “pseudo transition state” structures, is computationally efficient and suitable for the discovery and optimization of artificial enzymes. Alternatively, this approach can be applied on systems for which a large conformational sampling is needed to identify relevant transition states.
Max TON: ---ee: 96Notes: Prediction of the enantioselectivity by computational methods.
Computationally Driven Design of an Artificial Metalloenzyme Using Supramolecular Anchoring Strategies of Iridium Complexes to Alcohol Dehydrogenase
Faraday Discuss. 2022, 10.1039/d1fd00070e
Artificial metalloenzymes (ArMs) confer non-biological reactivities to biomolecules, whilst taking advantage of the biomolecular architecture in terms of their selectivity and renewable origin. In particular, the design of ArMs by the supramolecular anchoring of metal catalysts to protein hosts provides flexible and easy to optimise systems. The use of cofactor dependent enzymes as hosts gives the advantage of both a (hydrophobic) binding site for the substrate and a cofactor pocket to accommodate the catalyst. Here, we present a computationally driven design approach of ArMs for the transfer hydrogenation reaction of cyclic imines, starting from the NADP+-dependent alcohol dehydrogenase from Thermoanaerobacter brockii (TbADH). We tested and developed a molecular docking workflow to define and optimize iridium catalysts with high affinity for the cofactor binding site of TbADH. The workflow uses high throughput docking of compound libraries to identify key structural motifs for high affinity, followed by higher accuracy docking methods on smaller, focused ligand and catalyst libraries. Iridium sulfonamide catalysts were selected and synthesised, containing either a triol, a furane, or a carboxylic acid to provide the interaction with the cofactor binding pocket. IC50 values of the resulting complexes during TbADH-catalysed alcohol oxidation were determined by competition experiments and were between 4.410 mM and 0.052 mM, demonstrating the affinity of the iridium complexes for either the substrate or the cofactor binding pocket of TbADH. The catalytic activity of the free iridium complexes in solution showed a maximal turnover number (TON) of 90 for the reduction of salsolidine by the triol-functionalised iridium catalyst, whilst in the presence of TbADH, only the iridium catalyst with the triol anchoring functionality showed activity for the same reaction (TON of 36 after 24 h). The observation that the artificial metalloenzymes developed here lacked stereoselectivity demonstrates the need for the further investigation and optimisation of the ArM. Our results serve as a starting point for the design of robust artificial metalloenzymes, exploiting supramolecular anchoring to natural NAD(P)H binding pockets.
Host protein: Alcohol dehydrogenaseMax TON: 81±0.80ee: ---PDB: 1YKFNotes: ---
Controlled Ligand Exchange Between Ruthenium Organometallic Cofactor Precursors and a Naïve Protein Scaffold Generates Artificial Metalloenzymes Catalysing Transfer Hydrogenation
Angew. Chem. Int. Ed. 2021, 60, 10919-10927, 10.1002/anie.202015834
Many natural metalloenzymes assemble from proteins and biosynthesised complexes, generating potent catalysts by changing metal coordination. Here we adopt the same strategy to generate artificial metalloenzymes (ArMs) using ligand exchange to unmask catalytic activity. By systematically testing RuII(η6-arene)(bipyridine) complexes designed to facilitate the displacement of functionalised bipyridines, we develop a fast and robust procedure for generating new enzymes via ligand exchange in a protein that has not evolved to bind such a complex. The resulting metal cofactors form peptidic coordination bonds but also retain a non-biological ligand. Tandem mass spectrometry and 19F NMR spectroscopy were used to characterise the organometallic cofactors and identify the protein-derived ligands. By introduction of ruthenium cofactors into a 4-helical bundle, transfer hydrogenation catalysts were generated that displayed a 35-fold rate increase when compared to the respective small molecule reaction in solution.
Ligand type: Arene; BipyridineHost protein: Cytochrome b562Anchoring strategy: DativeOptimization: ---Notes: 35 fold rate increase
Ligand type: Arene; BipyridineHost protein: UbiquitinAnchoring strategy: DativeOptimization: ---Notes: 35 fold rate increase
Cross-Regulation of an Artificial Metalloenzyme
Angew. Chem. Int. Ed. 2017, 56, 10156-10160, 10.1002/anie.201702181
Cross‐regulation of complex biochemical reaction networks is an essential feature of living systems. In a biomimetic spirit, we report on our efforts to program the temporal activation of an artificial metalloenzyme via cross‐regulation by a natural enzyme. In the presence of urea, urease slowly releases ammonia that reversibly inhibits an artificial transfer hydrogenase. Addition of an acid, which acts as fuel, allows to maintain the system out of equilibrium.
Max TON: 96ee: ---PDB: ---Notes: Cross-regulated reduction of the antibiotic enrofloxacin by an ArM.
Directed Evolution of an Artificial Imine Reductase
Angew. Chem. Int. Ed. 2018, 57, 1863-1868, 10.1002/anie.201711016
Artificial metalloenzymes, resulting from incorporation of a metal cofactor within a host protein, have received increasing attention in the last decade. The directed evolution is presented of an artificial transfer hydrogenase (ATHase) based on the biotin‐streptavidin technology using a straightforward procedure allowing screening in cell‐free extracts. Two streptavidin isoforms were yielded with improved catalytic activity and selectivity for the reduction of cyclic imines. The evolved ATHases were stable under biphasic catalytic conditions. The X‐ray structure analysis reveals that introducing bulky residues within the active site results in flexibility changes of the cofactor, thus increasing exposure of the metal to the protein surface and leading to a reversal of enantioselectivity. This hypothesis was confirmed by a multiscale approach based mostly on molecular dynamics and protein–ligand dockings.
Max TON: 380ee: 95PDB: 6ESSNotes: Salsolidine formation; Sav mutant S112A-N118P-K121A-S122M: (R)-selective
Max TON: 220ee: 85PDB: 6ESUNotes: Salsolidine formation; Sav mutant S112R-N118P-K121A-S122M-L124Y: (S)-selective
Efficient in Situ Regeneration of NADH Mimics by an Artificial Metalloenzyme
ACS Catal. 2016, 6, 3553-3557, 10.1021/acscatal.6b00258
NADH mimics (mNADHs) have been shown to accelerate and orthogonally activate ene reductase-catalyzed reactions. However, existing regeneration methods of NAD(P)H fail for mNADHs. Catalysis with artificial metalloenzymes based on streptavidin (Sav) variants and a biotinylated iridium cofactor enable mNADH regeneration with formate. This regeneration can be coupled with ene reductase-catalyzed asymmetric reduction of α,β-unsaturated compounds, because of the protective compartmentalization of the organometallic cofactor. With 10 mol % mNAD+, a preparative scale reaction (>100 mg) gave full conversion with 98% ee, where TTNs reached 2000, with respect to the Ir cofactor under ambient atmosphere in aqueous medium.
Max TON: >1980ee: ---PDB: ---Notes: ArM works in combination with the ene reductase (ER) of the Old Yellow Enzyme family fromThermus scotuductus (TsOYE).
Evaluation of Chemical Diversity of Biotinylated Chiral 1,3-Diamines as a Catalytic Moiety in Artificial Imine Reductase
ChemCatChem 2016, 8, 1665-1670, 10.1002/cctc.201600116
The possibility of obtaining an efficient artificial imine reductase was investigated by introducing a chiral cofactor into artificial metalloenzymes based on biotin–streptavidin technology. In particular, a chiral biotinylated 1,3‐diamine ligand in coordination with iridium(III) complex was developed. Optimized chemogenetic studies afforded positive results in the stereoselective reduction of a cyclic imine, the salsolidine precursor, as a standard substrate with access to both enantiomers. Various factors such as pH, temperature, number of binding sites, and steric hindrance of the catalytic moiety have been proved to affect both efficiency and enantioselectivity, underlining the great flexibility of this system in comparison with the achiral system. Computational studies were also performed to explain how the metal configuration, in the proposed system, might affect the observed stereochemical outcome.
Max TON: >99ee: 83Notes: ---
Expanding the Chemical Diversity in Artificial Imine Reductases Based on the Biotin–Streptavidin Technology
ChemCatChem 2014, 6, 1010-1014, 10.1002/cctc.201300825
We report on the optimization of an artificial imine reductase based on the biotin‐streptavidin technology. With the aim of rapidly generating chemical diversity, a novel strategy for the formation and evaluation of biotinylated complexes is disclosed. Tethering the biotin‐anchor to the Cp* moiety leaves three free coordination sites on a d6 metal for the introduction of chemical diversity by coordination of a variety of ligands. To test the concept, 34 bidentate ligands were screened and a selection of the 6 best was tested in the presence of 21 streptavidin (Sav) isoforms for the asymmetric imine reduction by the resulting three legged piano stool complexes. Enantiopure α‐amino amides were identified as promising bidentate ligands: up to 63 % ee and 190 turnovers were obtained in the formation of 1‐phenyl‐1,2,3,4‐tetrahydroisoquinoline with [IrCp*biotin(L‐ThrNH2)Cl]⊂SavWT as a catalyst.
Max TON: 188ee: 43PDB: ---Notes: ---
Ligand type: Amino carboxylic acid; Cp*Max TON: 4ee: 21PDB: ---Notes: ---
Ligand type: Cp*Notes: ---
Ligand type: Cp*; Pyrazine amideMax TON: 26ee: 16PDB: ---Notes: ---
Ligand type: Bipyridine; Cp*Notes: ---
Max TON: 12ee: 13PDB: ---Notes: ---
Max TON: 102ee: 14PDB: ---Notes: ---
Max TON: 94ee: 67PDB: ---Notes: ---
Ligand type: Amino amide; Cp*Max TON: 10ee: 7PDB: ---Notes: ---
Ligand type: Amino carboxylic acid; Cp*Max TON: 8ee: 1PDB: ---Notes: ---
Ligand type: Cp*Notes: ---
Ligand type: Cp*; Pyrazine amideNotes: ---
Ligand type: Bipyridine; Cp*Max TON: 4ee: 6PDB: ---Notes: ---
Max TON: 8ee: 0PDB: ---Notes: ---
Ferritin Encapsulation of Artificial Metalloenzymes: Engineering a Tertiary Coordination Sphere for an Artificial Transfer Hydrogenase
Dalton Trans. 2018, 47, 10837-10841, 10.1039/C8DT02224K
Ferritin, a naturally occuring iron-storage protein, plays an important role in nanoengineering and biomedical applications. Upon iron removal, apoferritin was shown to allow the encapsulation of an artificial transfer hydrogenase (ATHase) based on the streptavidin-biotin technology. The third coordination sphere, provided by ferritin, significantly influences the catalytic activity of an ATHase for the reduction of cyclic imines.
Max TON: 3874ee: 75PDB: ---Notes: ---
Fluorescence-Based Assay for the Optimization of the Activity of Artificial Transfer Hydrogenase within a Biocompatible Compartment
ChemCatChem 2013, 5, 720-723, 10.1002/cctc.201200834
The time capsules: The transfer hydrogenation of an enone‐bound fluorogenic compound by an artificial metalloenzyme leads to the release of fluorescent compound umbelliferone. Upon encapsulation of the hybrid catalyst inside a biocompatible compartment, the activity of the transfer hydrogenase is maintained for several months, even at micromolar concentrations.
Genetic Engineering of an Artificial Metalloenzyme for Transfer Hydrogenation of a Self-Immolative Substrate in Escherichia coli’s Periplasm
J. Am. Chem. Soc. 2018, 140, 13171-13175, 10.1021/jacs.8b07189
Artificial metalloenzymes (ArMs), which combine an abiotic metal cofactor with a protein scaffold, catalyze various synthetically useful transformations. To complement the natural enzymes’ repertoire, effective optimization protocols to improve ArM’s performance are required. Here we report on our efforts to optimize the activity of an artificial transfer hydrogenase (ATHase) using Escherichia coli whole cells. For this purpose, we rely on a self-immolative quinolinium substrate which, upon reduction, releases fluorescent umbelliferone, thus allowing efficient screening. Introduction of a loop in the immediate proximity of the Ir-cofactor afforded an ArM with up to 5-fold increase in transfer hydrogenation activity compared to the wild-type ATHase using purified mutants.
Max TON: 1000ee: 76PDB: 6GMINotes: ---
Genetic Optimization of the Catalytic Efficiency of Artificial Imine Reductases Based on Biotin−Streptavidin Technology
ACS Catal. 2013, 3, 1752-1755, 10.1021/cs400428r
Artificial metalloenzymes enable the engineering of the reaction microenvironment of the active metal catalyst by modification of the surrounding host protein. We report herein the optimization of an artificial imine reductase (ATHase) based on biotin–streptavidin technology. By introduction of lipophilic amino acid residues around the active site, an 8-fold increase in catalytic efficiency compared with the wild type imine reductase was achieved. Whereas substrate inhibition was encountered for the free cofactor and wild type ATHase, two engineered systems exhibited classical Michaelis–Menten kinetics, even at substrate concentrations of 150 mM with measured rates up to 20 min–1.
Max TON: ---ee: 60PDB: ---Notes: ---
High-Level Secretion of Recombinant Full-Length Streptavidin in Pichia Pastoris and its Application to Enantioselective Catalysis
Protein Expression Purif. 2014, 93, 54-62, 10.1016/j.pep.2013.10.015
Artificial metalloenzymes result from the incorporation of a catalytically competent biotinylated organometallic moiety into full-length (i.e. mature) streptavidin. With large-scale industrial biotechnology applications in mind, large quantities of recombinant streptavidin are required. Herein we report our efforts to produce wild-type mature and biotin-free streptavidin using the yeast Pichia pastoris expression system. The streptavidin gene was inserted into the expression vector pPICZαA in frame with the Saccharomyces cerevisiae α-mating factor secretion signal. In a fed-batch fermentation using a minimal medium supplemented with trace amounts of biotin, functional streptavidin was secreted at approximately 650 mg/L of culture supernatant. This yield is approximately threefold higher than that from Escherichia coli, and although the overall expression process takes longer (ten days vs. two days), the downstream processing is simplified by eliminating denaturing/refolding steps. The purified streptavidin bound ∼3.2 molecules of biotin per tetramer. Upon incorporation of a biotinylated piano-stool catalyst, the secreted streptavidin displayed identical properties to streptavidin produced in E. coli by showing activity as artificial imine reductase.
Max TON: 152ee: 61PDB: ---Notes: Sav expression in E. coli
Max TON: 158ee: 64PDB: ---Notes: Sav expression in P. pastoris
Human Carbonic Anhydrase II as Host Protein for the Creation of Artificial Metalloenzymes: The Asymmetric Transfer Hydrogenation of Imines
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).
Max TON: 47ee: 70PDB: ---Notes: ---
Immobilization of an Artificial Imine Reductase Within Silica Nanoparticles Improves its Performance
Chem. Commun. 2016, 52, 9462-9465, 10.1039/c6cc04604e
Silica nanoparticles equipped with an artificial imine reductase display remarkable activity towards cyclic imine- and NAD+ reduction. The method, based on immobilization and protection of streptavidin on silica nanoparticles, shields the biotinylated metal cofactor against deactivation yielding over 46 000 turnovers in pure samples and 4000 turnovers in crude cellular extracts.
Max TON: 4554ee: 89PDB: ---Notes: Reaction in nanoparticles
Improving the Catalytic Performance of an Artificial Metalloenzyme by Computational Design
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.
Ligand type: Cp*; Pyridine sulfonamideMax TON: 100ee: 96PDB: ---Notes: ---
Improving the Enantioselectivity of Artificial Transfer Hydrogenases Based on the Biotin–Streptavidin Technology by Combinations of Point Mutations
Inorg. Chim. Acta 2010, 363, 601-604, 10.1016/j.ica.2009.02.001
Artificial metalloenzymes based on the incorporation of biotinylated ruthenium piano–stool complexes within streptavidin can be readily optimized by chemical or genetic means. We performed genetic modifications of such artificial metalloenzymes for the transfer hydrogenation of aromatic ketones, by combining targeted point mutations of the host protein. Upon using the P64G-L124V double mutant of streptavidin in combination with the [η6-(p-cymene)Ru(Biot-p-L)Cl] complex, the enantioselectivity can be increased up to 98% ee (R) for the reduction of p-methylacetophenone, which is the highest selectivity obtained up to date with an artificial transfer hydrogenase.
Max TON: 98ee: 98PDB: ---Notes: ---
Max TON: 24ee: 84PDB: 2QCBNotes: ---