Redox-reversible artificial metalloenzymes

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As natural biocatalysts, enzymes have evolved over billions or years to be highly efficient and selective. Their application in both bioconversions and chemical syntheses is attractive because of their sustainability and environmental compatibility. However, for many applications, suitable naturally occurring enzymes are not available. Tailor-made artificial metalloenzymes, on the other hand, can combine the selectivity and biocompatibility of proteins with the reactivity and the reaction scope of synthetic catalysts and thus have the potential to expand the range of applications in which biocatalysts can be used, for example by making new-to-nature transformations accessible. Artificial metalloenzymes have not yet progressed into general use, mainly because the proteins and the catalysts are challenging and expensive to produce and, when the artificial enzyme is no longer required or active, its valuable components cannot easily be recycled.Inspired by the way bacteria acquire essential iron, we have developed a new iron-based anchor unit that connects synthetic catalysts to proteins, creating artificial enzymes, but on chemical reduction of the iron centre, the anchor unit disconnects and triggers the disassembly of the artificial enzymes. Hence both the protein and the synthetic catalyst can be recovered and recycled.In this project, we will explore the wider scope of these recyclable artificial enzymes and immobilise the protein scaffolds on solid supports to enable their integration into flow systems. In this way, the removal and replacement of catalysts that have lost activity becomes possible. Subsequent replacements with different catalysts would be of particular interest since this would not only allow the protein to be recycled but also enabling an easy switch from one catalysed reaction to another. The application of this 'catch-and-release' approach to immobilised artificial metalloenzyme design will provide a flexible toolbox for their preparation that allows catalysts, protein scaffolds and solid supports to be mixed, matched and recycled, for us and others to use, adapt and explore further, both in batch processes and in continuous flow.