De Novo Design of Catalytically Active Salen-Binding Proteins

De novo design of catalytic metalloproteins has the potential to generate enzymes that combine the efficiency of natural proteins with the reactivity of synthetic organometallic catalysts. Here, we develop a computational strategy to design enzymes with novel tertiary structures that bind metal salen complexes, classic small-molecule catalysts not found in biology. Six proteins were designed and screened for function; five of six express well, bind a Co-salen cofactor, and catalyze a transition metal hydrogen atom transfer (MHAT)-mediated deallylation reaction, representing the first de novo proteins to catalyze this class of transformation. The spectroscopic properties and crystal structure of the most active sequence were in excellent agreement with the design, and the holoprotein retained its structure and activity over a broad range of pH (2–12), temperatures up to 95 °C, and aqueous/organic solvent mixtures. We suggest that the combinatorial space provided by metal ion identity, ligand substitution, and active site structure can be used to generate artificial metalloenzymes that catalyze many chemical transformations.