Bidirectional Electron Transfer by a [2Fe-2S]_Rieske Cluster Enables HO–FeIII═O•– Chemistry for cis-Dihydroxylation

Iron–sulfur ([FeS]) clusters often work as unidirectional electron-transfer conduits in metalloenzymes. Herein, we demonstrate that the [2Fe-2S]Rieske cluster in terephthalate 1,2-dioxygenase (TPADO) functions as a dynamic electron reservoir capable of bidirectional electron transfer during catalysis. Using density functional theory, we reveal that the TPADO reaction is driven by a previously unrecognized Rieske-assisted HO–FeIII═O•– species, rather than the canonical high-valent iron(V)-oxo. The Rieske cluster actively donates and retrieves electrons during O–O bond cleavage and substrate oxidation. Productive cis-dihydroxylation proceeds via stepwise oxo-initiated radical pathways, while Fe-OOH and epoxide-based mechanisms are ruled out by prohibitive barriers. These findings highlight the mechanistic role of Rieske clusters in oxygen activation, expanding the conceptual framework of both [FeS]-dependent and Fe-dependent catalysis.