Designed Rubredoxin miniature in a fully artificial electron chain triggered by visible light

Designing metal sites into de novo proteins has significantly improved, recently. However, identifying the minimal coordination spheres, able to encompass the necessary information for metal binding and activity, still represents a great challenge, today. Here, we test our understanding with a benchmark, nevertheless difficult, case. We assemble into a miniature 28-residue protein, the quintessential elements required to fold properly around a FeCys(4) redox center, and to function efficiently in electron-transfer. This study addresses a challenge in de novo protein design, as it reports the crystal structure of a designed tetra-thiolate metal-binding protein in sub-angstrom agreement with the intended design. This allows us to well correlate structure to spectroscopic and electrochemical properties. Given its high reduction potential compared to natural and designed FeCys(4)-containing proteins, we exploit it as terminal electron acceptor of a fully artificial chain triggered by visible light.Living organisms regulate their energy demand by managing electron trafficking in complex transport chains. Here, the authors pioneer a fully artificial electron chain triggered by visible light using designed proteins, unlocking possibilities in bioengineering.