Designing an Artificial Metalloenzyme for Re-based CO2 Photoreduction

The conversion of CO₂ into value-added chemicals using sunlight is a major goal in sustainable chemistry. Here, we report the design and chemogenetic optimization of a Re(I)-based artificial metalloenzyme (ArM) for the photocatalytic reduction of CO₂ to CO in aqueous solution. By incorporating a biotinylated Re(I)-phenanthroline catalyst into a tetrameric streptavidin scaffold, we achieved a significant enhancement in catalytic turnover compared to free catalyst. Mutational screening at viable positions Ser112 and Lys121 revealed a range of catalytic activities, highlighting the tunability of the system. Through a combination of molecular dynamics simulations and experimental characterization, we demonstrate that the catalytic turnover number correlates strongly with the accessibility of CO₂ to the catalyst's active site, a factor not considered in free solution catalyst design, and further computation reveals the variable activation of a bound CO2 among mutants. This work establishes a clear design principle for enhancing Re(I)-based photocatalysis by leveraging the second coordination sphere of a protein scaffold to confer aqueous stability and control substrate access.