Janda, K.D.; Lerner, R.A.

J. Am. Chem. Soc. 1993, 115, 4906-4907, 10.1021/ja00064a068

n/a

Akabori, S.; Sakurai, S.

Nature 1956, 178, 323-324, 10.1038/178323b0

Asymmetric synthesis has hitherto succeeded only by using reagents or solvents having the asymmetric configuration.

Marchetti, M.

Adv. Synth. Catal. 2002, 344, 556, 10.1002/1615-4169(200207)344:5<556::AID-ADSC556>3.0.CO;2-E

The water‐soluble complex derived from Rh(CO)2(acac) and human serum albumin (HSA) proved to be efficient in the hydroformylation of several olefin substrates. The chemoselectivity and regioselectivity were generally higher than those obtained by using the classic catalytic systems like TPPTS‐Rh(I) (TPPTS=triphenylphosphine‐3,3′,3″‐trisulfonic acid trisodium salt). Styrene and 1‐octene, for instance, were converted in almost quantitative yields into the corresponding oxo‐aldehydes at 60 °C and 70 atm (CO/H2=1) even at very low Rh(CO)2(acac)/HSA catalyst concentrations. The possibility of easily recovering the Rh(I) compound makes the system environmentally friendly. The circular dichroism technique was useful for demonstrating the Rh(I) binding to the protein and to give information on the stability in solution of the catalytic system. Some other proteins have been used to replace HSA as complexing agent for Rh(I). The results were less impressive than those obtained using HSA and their complexes with Rh(I) were much less stable.

Lu, Y.

J. Am. Chem. Soc. 2004, 126, 10812-10813, 10.1021/ja046908x

Introducing nonnative metal ions or metal-containing prosthetic groups into a protein can dramatically expand the repertoire of its functionalities and thus its range of applications. Particularly challenging is the control of substrate-binding and thus reaction selectivity such as enantioselectivity. To meet this challenge, both non-covalent and single-point attachments of metal complexes have been demonstrated previously. Since the protein template did not evolve to bind artificial metal complexes tightly in a single conformation, efforts to restrict conformational freedom by modifying the metal complexes and/or the protein are required to achieve high enantioselectivity using the above two strategies. Here we report a novel site-selective dual anchoring (two-point covalent attachment) strategy to introduce an achiral manganese salen complex (Mn(salen)), into apo sperm whale myoglobin (Mb) with bioconjugation yield close to 100%. The enantioselective excess increases from 0.3% for non-covalent, to 12.3% for single point, and to 51.3% for dual anchoring attachments. The dual anchoring method has the advantage of restricting the conformational freedom of the metal complex in the protein and can be generally applied to protein incorporation of other metal complexes with minimal structural modification to either the metal complex or the protein.

Watanabe, Y.

J. Am. Chem. Soc. 2005, 127, 6556-6562, 10.1021/ja045995q

New methods for the synthesis of artificial metalloenzymes are important for the construction of novel biocatalysts and biomaterials. Recently, we reported new methodology for the synthesis of artificial metalloenzymes by reconstituting apo-myoglobin with metal complexes (Ohashi, M. et al., Angew Chem., Int. Ed.2003, 42, 1005−1008). However, it has been difficult to improve their reactivity, since their crystal structures were not available. In this article, we report the crystal structures of MIII(Schiff base)·apo-A71GMbs (M = Cr and Mn). The structures suggest that the position of the metal complex in apo-Mb is regulated by (i) noncovalent interaction between the ligand and surrounding peptides and (ii) the ligation of the metal ion to proximal histidine (His93). In addition, it is proposed that specific interactions of Ile107 with 3- and 3‘-substituent groups on the salen ligand control the location of the Schiff base ligand in the active site. On the basis of these results, we have successfully controlled the enantioselectivity in the sulfoxidation of thioanisole by changing the size of substituents at the 3 and 3‘ positions. This is the first example of an enantioselective enzymatic reaction regulated by the design of metal complex in the protein active site.

Sheldon, R.A.

Chem. Commun. 1998, 1891-1892, 10.1039/a804702b

Phytase (E.C. 3.1.3.8), which in vivo mediates the hydrolysis of phosphate esters, catalyses the enantioselective oxidation of thioanisole with H2O2, both in the presence and absence of vanadate ion, affording the S-sulfoxide in up to 66% ee at 100% conversion.

Schultz, P.G.

Science 1987, 238, 1401-1403, 10.1126/science.3685986

The relatively nonspecific single-stranded deoxyribonuclease, staphylococcal nuclease, was selectively fused to an oligonucleotide binding site of defined sequence to generate a hybrid enzyme. A cysteine was substituted for Lys116 in the enzyme by oligonucleotide-directed mutagenesis and coupled to an oligonucleotide that contained a 3'-thiol. The resulting hybrid enzyme cleaved single-stranded DNA at sites adjacent to the oligonucleotide binding site.

Ward, T.R.

J. Organomet. Chem. 2009, 694, 930-936, 10.1016/j.jorganchem.2008.11.023

Incorporation of achiral biotinylated manganese-salen complexes into streptavidin yields artificial metalloenzymes for aqueous sulfoxidation using hydrogen peroxide. Four biotinylated salen ligands were synthesized and their manganese complexes were tested in combination with several streptavidin mutants, yielding moderate conversions (up to 56%) and low enantioselectivities (maximum of 13% ee) for the sulfoxidation of thioanisole.

Pan, Y.

RSC Adv. 2013, 3, 22976, 10.1039/c3ra43784a

Horseradish Peroxidase (HRP) is a commercially available and prevalently used peroxidase with no specific substrate binding domain. However, after being incorporated with different metal cations, new catalytic functions were found in biomimetic oxidation of resveratrol. Based on the results of screening, Ca, Cu, Fe and Mn incorporated enzymes showed distinctive effects, either decomposition or dimerization products were observed.

Lu, Y.

Chem. - Eur. J. 2009, 15, 7481-7489, 10.1002/chem.200802449

To demonstrate protein modulation of metal‐cofactor reactivity through noncovalent interactions, pH‐dependent sulfoxidation and 2,2′‐azino‐bis(3‐ethylbenzthiazoline‐6‐sulphonic acid) (ABTS) oxidation reactivity of a designed myoglobin (Mb) containing non‐native Mn–salen complex (1) was investigated using H2O2 as the oxidant. Incorporation of 1 inside the Mb resulted in an increase in the turnover numbers through exclusion of water from the metal complex and prevention of Mn–salen dimer formation. Interestingly, the presence of protein in itself is not enough to confer the increase activity as mutation of the distal His64 in Mb to Phe to remove hydrogen‐bonding interactions resulted in no increase in the turnover numbers, while mutation His64 to Arg, another residue with ability to hydrogen‐bond interactions, resulted in an increase in reactivity. These results strongly suggest that the distal ligand His64, through its hydrogen‐bonding interaction, plays important roles in enhancing and fine‐tuning reactivity of the Mn–salen complex. Nonlinear least‐squares fitting of rate versus pH plots demonstrates that 1⋅Mb(H64X) (X=H, R and F) and the control Mn–salen 1 exhibit pKa values varying from pH 6.4 to 8.3, and that the lower pKa of the distal ligand in 1⋅Mb(H64X), the higher the reactivity it achieves. Moreover, in addition to the pKa at high pH, 1⋅Mb displays another pKa at low pH, with pKa of 5.0±0.08. A comparison of the effect of different pH on sulfoxidation and ABTS oxidation indicates that, while the intermediate produced at low pH conditions could only perform sulfoxidation, the intermediate at high pH could oxidize both sulfoxides and ABTS. Such a fine‐control of reactivity through hydrogen‐bonding interactions by the distal ligand to bind, orient and activate H2O2 is very important for designing artificial enzymes with dramatic different and tunable reactivity from catalysts without protein scaffolds.

Tiller, J.C.

ChemCatChem 2016, 8, 593-599, 10.1002/cctc.201501083

The Sharpless dihydroxylation of styrene with the artificial metalloenzyme osmate‐laccase‐poly(2‐methyloxazoline) was investigated to find reaction conditions that allow this unique catalyst to reveal its full potential. After changing the co‐oxidizing agent to tert‐butyl hydroperoxide and optimizing the osmate/enzyme ratio, the turnover frequency and the turnover number could be increased by an order of magnitude, showing that the catalyst can compete with classical organometallic catalysts. Varying the metal in the active center showed that osmate is by far the most active catalytic center, but the reaction can also be realized with permanganate and iron(II) salts.

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.

Lu, Y.

Chem. Commun. 2008, 1665, 10.1039/b718915j

We demonstrate that incorporation of MnSalen into a protein scaffold enhances the chemoselectivity in sulfoxidation of thioanisole and find that both the polarity and hydrogen bonding of the protein scaffold play an important role in tuning the chemoselectivity.

Imperiali, B.

Prot. Eng. 1997, 10, 691-698, 10.1093/protein/10.6.691

The transaminase activity of two new semisynthetic RNase-S proteins incorporating a pyridoxamine moiety at the active site has been evaluated. A chemically competent derivative of pyridoxamine phosphate was incorporated into the C-peptide fragments of these non-covalent protein complexes in the form of an unnatural coenzyme-amino acid chimera, 'Pam'. The chimeric Pam residue integrates the heterocyclic functionality of pyridoxamine phosphate into the side chain of an alpha-amino acid and was introduced instead of Phe8 into the C-peptide sequence via standard solid phase methodology. The two semisynthetic Pam-RNase constructs were designed to probe whether the native ribonuclease catalytic machinery could be enlisted to modulate a pyridoxamine-dependent transamination reaction. Both RNase complexes, H1SP and S1SP, exhibited modest rate enhancements in the Cu(II)-assisted transamination of pyruvate to alanine under single turnover conditions, relative to 5'-deoxypyridoxamine and the uncomplexed C-peptide fragments. Furthermore, multiple turnovers of substrates were achieved in the presence of added L-phenylalanine due to recycling of the pyridoxamine moiety. The modest chiral inductions observed in the catalytic production of alanine and the differences in reactivity between the two proteins could be rationalized by the participation of a general base (His12) in complex H1SP, and by the increased tolerance for large amino acid substrates by complex S1SP, which contains serine at this position. The pyridoxamine-amino acid chimera will be useful in the future for examining the coenzyme structure/ function relationships in a native-like peptidyl architecture.

Kokubo, T.; Okano, M.

J. Chem. Soc., Chem. Commun. 1983, 0, 769-770, 10.1039/C39830000769

The 1:1 complex between an osmate ester and bovine serum albumin was found to be effective as an enantioselective catalyst in the cis-hydroxylation of alkenes, affording diols in up to 68% e.e. and turnover of the catalyst with t-butyl hydroperoxide.

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.

Cavazza, C.; Ménage, S.

ChemBioChem 2009, 10, 545-552, 10.1002/cbic.200800595

Magic Mn–salen metallozyme: The design of an original, artificial, inorganic, complex‐protein adduct, has led to a better understanding of the synergistic effects of both partners. The exclusive formation of sulfoxides by the hybrid biocatalyst, as opposed to sulfone in the case of the free inorganic complex, highlights the modulating role of the inorganic‐complex‐binding site in the protein.

Reetz, M.T.

Chimia 2002, 56, 721-723, 10.2533/000942902777679920

The first step in applying the recently proposed concept concerning the application of directed evolution to the creation of selective hybrid catalysts is described, specifically the covalent attachment of Mn-salen moieties and of Cu-, Pd-, and Rh-complexes of dipyridine derivatives as well as the implantation of a diphosphine moiety in a protein, future steps being cycles of mutagenesis/screening.