An interfacial-intramolecular electron highway for accelerated electrocatalytic CO2 reduction by an O2-tolerant formate dehydrogenase

Bioelectrocatalytic CO₂ reduction offers a sustainable route for CO₂ bioconversion, yet remains limited by interfacial-intramolecular electron transfer and oxygen sensitivity. Here, we mine a formate dehydrogenase from Shewanella oneidensis MR-1 (SoFdhAB) featuring completely oxygen tolerant and direct-electron-transfer (DET) electrocatalytic performances. Cryo-electron microscopy (Cryo-EM) analysis reveals an intramolecular electron highway comprising five [4Fe-4S] clusters, a regional face-face contact facilitating interfacial ET, and a unique oxygen resistance mechanism different from inactivation-activation. By acquiring a beneficial variant SoFdhAB-Y94S, a direct bioelectrocatalytic CO₂ reduction system is constructed, accumulating 2.88 ± 0.03 mmol formate in 64 hours with a steady rate of 45.3 ± 0.5 μmol h^-1 cm^-2 and a Faradaic efficiency of 93.1 ± 5.2%. The merits of oxygen tolerance and efficient (electro)catalytic property endow SoFdhAB a robust enzyme adopted in potential application scenarios, and the inherent DET capability may inspire the interfacial engineering of other oxidoreductases.