Design and engineering of artificial metalloproteins: from de novo metal coordination to catalysis

Metalloproteins are essential to sustain life. Natural evolution optimized them for intricate structural, regulatory and catalytic functions that cannot be fulfilled by either a protein or a metal ion alone. In order to understand this synergy and the complex design principles behind the natural systems, simpler mimics were engineered from the bottom up by installing de novo metal sites in either natural or fully designed, artificial protein scaffolds. This review focuses on key challenges associated with this approach. We discuss how proteins can be equipped with binding sites that provide an optimal coordination environment for a metal cofactor of choice, which can be a single metal ion or a complex multinuclear cluster. Furthermore, we highlight recent studies in which artificial metalloproteins were engineered towards new functions, including electron transfer and catalysis. In this context, the powerful combination of de novo protein design and directed evolution is emphasized for metalloenzyme development.