Gras, E.; Hureau, C.

Coord. Chem. Rev. 2016, 308, 445-459, 10.1016/j.ccr.2015.05.011

Artificial metalloenzymes, with their high selectivity and specificity combined with a wide scope of reactivity and substrates, constitute an original approach for catalyst development. Different strategies have been proposed for their elaboration, proceeding from modification of natural enzymes using bioengineering methods to de novo protein design. Another bio-inspired methodology for the development of hybrid catalysts consists in the incorporation of coordination complexes into biomolecules, with the aim to upgrade their catalytic abilities. In these systems, the reaction performed by the naked catalyst is modulated by the well-defined structure of the host biomolecule. This conveys added value to the catalyst, such as enantioselectivity or chemoselectivity. DNA, apo-enzymes, proteins and peptides have been engaged in this approach, affording a wide diversity of reactivities and substrates. The resulting systems can then be improved by combined chemical and bioengineering optimization, allowing access to powerful catalysts. Because this approach can virtually be applied to any biomolecule or coordination complex, the elaboration of bio-based hybrid catalysts seems promising for advance in catalysis.

Holland, P.L.

J. Inorg. Biochem. 2021, 219, 111430, 10.1016/j.jinorgbio.2021.111430

Artificial metalloenzymes (ArMs) consist of an unnatural metal or cofactor embedded in a protein scaffold, and are an excellent platform for applying the concepts of protein engineering to catalysis. In this Focused Review, we describe the application of ArMs as simple, tunable artificial models of the active sites of complex natural metalloenzymes for small-molecule activation. In this sense, ArMs expand the strategies of synthetic model chemistry to protein-based supporting ligands with potential for participation from the second coordination sphere. We focus specifically on ArMs that are structural, spectroscopic, and functional models of enzymes for activation of small molecules like CO, CO2, O2, N2, and NO, as well as production/consumption of H2. These ArMs give insight into the identities and roles of metalloenzyme structural features within and near the cofactor. We give examples of ArM work relevant to hydrogenases, acetyl-coenzyme A synthase, superoxide dismutase, heme oxygenases, nitric oxide reductase, methyl-coenzyme M reductase, copper-O2 enzymes, and nitrogenases.

Arold, S.T.; Eppinger, J.; Groll, M.

ACS Catal. 2019, 9, 11371-11380, 10.1021/acscatal.9b02896

Artificial metalloenzymes (ArMs) have high potential in biotechnological applications as they combine the versatility of transition-metal catalysis with the substrate selectivity of enzymes. An ideal host protein should allow high-yield recombinant expression, display thermal and solvent stability to withstand harsh reaction conditions, lack nonspecific metal-binding residues, and contain a suitable cavity to accommodate the artificial metal site. Moreover, to allow its rational functionalization, the host should provide an intrinsic reporter for metal binding and structural changes, which should be readily amendable to high-resolution structural characterization. Herein, we present the design, characterization, and de novo functionalization of a fluorescent ArM scaffold, named mTFP*, that achieves these characteristics. Fluorescence measurements allowed direct assessment of the scaffold’s structural integrity. Protein X-ray structures and transition metal Förster resonance energy transfer (tmFRET) studies validated the engineered metal coordination sites and provided insights into metal binding dynamics at the atomic level. The implemented active metal centers resulted in ArMs with efficient Diels–Alderase and Friedel–Crafts alkylase activities.