Synergistic Substrate and Oxygen Activation in Salicylate Dioxygenase Revealed by QM/MM Simulations

Salicylate 1,2‐dioxygenase (SDO) is the first enzyme to be discovered to catalyze the oxidative cleavage of a monohydroxylated aromatic compound, namely salicylate, instead of the well‐known electron‐rich substrates. We have investigated the mechanism of dioxygen activation in SDO by QM/MM calculations. Our study reveals that the non‐heme Fe II center in SDO activates salicylate and O 2 synergistically through a strong covalent interaction to facilitate the reductive cleavage of O 2 . A covalent salicylate–Fe II –O 2 complex is the reactive oxygen species in this case, and its electronic structure is best described as being between the two limiting cases, Fe II −O 2 and Fe II −O 2 .− , with partial electron transfer from the activated salicylate to O 2 via the Fe center. Thus SDO employs a synergistic strategy of substrate and oxygen activation to carry out the catalytic reaction, which is unprecedented in the family of iron dioxygenases. Moreover, O 2 activation in SDO happens without the assistance of a proton source. Our study essentially shows a new mechanistic possibility for O 2 activation.