Barker, P.D.; Boss, S.R.

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.

Arseniyadis, S.; Campagne, J.; Smietana, M.

Chem. Eur. J. 2020, 26, 3519-3523, 10.1002/chem.202000516

While artificial cyclases hold great promise in chemical synthesis, this work presents the first example of a DNA-catalyzed inverse electron-demand hetero-Diels–Alder (IEDHDA) between dihydrofuran and various α,β-unsaturated acyl imidazoles. The resulting fused bicyclic O,O-acetals containing three contiguous stereogenic centers are obtained in high yields (up to 99 %) and excellent diastereo- (up to >99:1 dr) and enantioselectivities (up to 95 % ee) using a low catalyst loading. Most importantly, these results show that the concept of DNA-based asymmetric catalysis can be expanded to new synthetic transformations offering an efficient, sustainable, and highly selective tool for the construction of chiral building blocks.

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.

Matsuo, T.

Tetrahedron Lett. 2019, 60, 151226, 10.1016/j.tetlet.2019.151226

Organic synthesis using biocatalysts has been developed over many years and is still a prominent area of research. In this context, various hybrid biocatalysts composed of a synthetic metal complex catalyst and a protein scaffold (i.e. artificial metalloenzymes) have been constructed. One of the most recent research areas in biocatalysts-mediated synthesis is CC bond/cleavage, the most important type of reaction in organic chemistry. Some of the artificial enzymes were applied to in-cell reactions as well as in vitro systems. The effects of the structural fluctuation in biomacromolecules on their functions have also been realized. This review article includes recent research examples of artificial metalloenzymes used to CC bond formation/cleavage. As a perspective, we also focus on how we apply protein dynamics factor for the creation of new generation artificial metalloenzymes.

Barker, P.D.; Boss, S.R.

Johnson Matthey Technol. Rev. 2020, 64, 407-418, 10.1595/205651320x15928204097766

Generation of artificial metalloenzymes (ArMs) has gained much inspiration from the general understanding of natural metalloenzymes. Over the last decade, a multitude of methods generating transition metal-protein hybrids have been developed and many of these new-to-nature constructs catalyse reactions previously reserved for the realm of synthetic chemistry. This perspective will focus on ArMs incorporating 4d and 5d transition metals. It aims to summarise the significant advances made to date and asks whether there are chemical strategies, used in nature to optimise metal catalysts, that have yet to be fully recognised in the synthetic enzyme world, particularly whether artificial enzymes produced to date fully take advantage of the structural and energetic context provided by the protein. Further, the argument is put forward that, based on precedence, in the majority of naturally evolved metalloenzymes the direct coordination bonding between the metal and the protein scaffold is integral to catalysis. Therefore, the protein can attenuate metal activity by positioning ligand atoms in the form of amino acids, as well as making non-covalent contributions to catalysis, through intermolecular interactions that pre-organise substrates and stabilise transition states. This highlights the often neglected but crucial element of natural systems that is the energetic contribution towards activating metal centres through protein fold energy. Finally, general principles needed for a different approach to the formation of ArMs are set out, utilising direct coordination inspired by the activation of an organometallic cofactor upon protein binding. This methodology, observed in nature, delivers true interdependence between metal and protein. When combined with the ability to efficiently evolve enzymes, new problems in catalysis could be addressed in a faster and more specific manner than with simpler small molecule catalysts.