Onoda, A.

Curr. Opin. Chem. Biol. 2015, 25, 133-140, 10.1016/j.cbpa.2014.12.041

Hydrogenase catalyses reversible transformation of H2 to H+ using an active site which includes an iron or nickel atom. Synthetic model complexes and molecular catalysts inspired by nature have unveiled the structural and functional basis of the active site with remarkable accuracy and this has led to the discovery of active synthetic catalysts. To further improve the activity of such molecular catalysts, both the first and outer coordination spheres should be well-organized and harmonized for an efficient shuttling of H+, electrons, and H2. This article reviews recent advances in the design and catalytic properties of artificial enzymes that mimic the hydrogenase active site and the outer coordination sphere in combination with a peptide or protein scaffold.

Onoda, A.; Salmain, M.

Bioorganometallic Chemistry: Applications in Drug Discovery, Biocatalysis, and Imaging 2014, 305-338, 10.1002/9783527673438.ch10

Enzymes are the catalysts of the living world. Nature has tailored proteins to catalyze an incredibly wide range of reactions with exquisite selectivity and efficiency under very mild conditions of temperature, pH, pressure, and so on. Protein engineering combined with molecular modeling techniques affords tailor‐made biocatalysts for the industrial production of chiral synthons. Nonetheless, endowing a given protein scaffold with a totally new activity remains a challenging task for the biochemist. Among the current strategies to impart proteins with unnatural activity, those dealing with the construction of artificial metalloenzymes are particularly promising. By definition, artificial metalloenzymes are hybrid catalysts resulting from the incorporation of a transition metal species within a biomacromolecular scaffold. The rationale behind this concept is to combine the wide catalytic scope of transition metal complexes with the high activity and selectivity of biocatalysts. In most of the hybrid catalysts reported so far, the roles devoted to both partners are clearly separated: the metal complex being responsible for reactivity, while the protein environment is used to induce selectivity in the chemical process. In that, artificial metalloenzymes truly resemble enzymes whose efficiency relies on both the active site and the second sphere of coordination (also called the outer coordination sphere). In this chapter, we intend to give an overview of the various anchoring strategies reported over the last decade for the controlled, site‐selective attachment of nonnative metal cofactors within protein matrices together with the activity/selectivity displayed by these hybrid enzymes.

Onoda, A.

J. Inorg. Biochem. 2016, 158, 55-61, 10.1016/j.jinorgbio.2015.12.026

A hybrid biocatalyst containing a metal terpyridine (tpy) complex within a rigid β-barrel protein nitrobindin (NB) is constructed. A tpy ligand with a maleimide group, N-[2-([2,2′:6′,2′′-terpyridin]-4′-yloxy)ethyl]maleimide (1), was covalently linked to Cys96 inside the cavity of NB to prepare a conjugate NB–1. Binding of Cu2 +, Zn2 +, or Co2 + ion to the tpy ligand in NB–1 was confirmed by UV–vis spectroscopy and ESI–TOF MS measurements. Cu2 +-bound NB–1 is found to catalyze a Diels–Alder reaction between azachalcone and cyclopentadiene in 22% yield, which is higher than that of the Cu2 +–tpy complex without the NB matrix. The results suggest that the hydrophobic cavity close to the copper active site within the NB scaffold supports the binding of the two substrates, dienophile and diene, to promote the reaction.

Hayashi, T; Onoda, A.

ChemBioChem 2021, 22, 679-685, 10.1002/cbic.202000681

Directed evolution of Cp*RhIII-linked nitrobindin (NB), a biohybrid catalyst, was performed based on an in vitro screening approach. A key aspect of this effort was the establishment of a high-throughput screening (HTS) platform that involves an affinity purification step employing a starch-agarose resin for a maltose binding protein (MBP) tag. The HTS platform enables efficient preparation of the purified MBP-tagged biohybrid catalysts in a 96-well format and eliminates background influence of the host E. coli cells. Three rounds of directed evolution and screening of more than 4000 clones yielded a Cp*RhIII-linked NB(T98H/L100K/K127E) variant with a 4.9-fold enhanced activity for the cycloaddition of acetophenone oximes with alkynes. It is confirmed that this HTS platform for directed evolution provides an efficient strategy for generating highly active biohybrid catalysts incorporating a synthetic metal cofactor.

Onoda, A.

ACS Catal. 2014, 4, 2645-2648, 10.1021/cs500392e

The hydrogen-evolving diiron complex, (μ-S)2Fe2(CO)6 with a tethered maleimide moiety was synthesized and covalently embedded within the cavity of a rigid β-barrel protein matrix by coupling a maleimide moiety to a cysteine residue within the β-barrel. The (μ-S)2Fe2(CO)6 core within the cavity was characterized by UV–vis absorption and a characteristic CO vibration determined by IR measurements. The diiron complex embedded within the cavity retains the necessary catalytic activity (TON up to 130 for 6 h) to evolve H2 via a photocatalytic cycle with a Ru photosensitizer in a solution of 100 mM ascorbate and 50 mM Tris/HCl at pH 4.0 and 25 °C.