The substrate-bound formylglycine generating enzyme forms a trigonal planar tris-thiolate Cu(i) complex ready for oxygen activation.

Molecular oxygen (O2) is a sustainable oxidation reagent. O2 is strongly oxidizing but kinetically stable and its final reaction product is water. For these reasons learning how to activate O2 and how to steer its reactivity along desired reaction pathways is a longstanding challenge in chemical research.[1] Activation of ground‐state diradical O2 can occur either via conversion to singlet oxygen or by one‐electron reduction to superoxide. Many enzymes facilitate activation of O2 by direct fomation of a metal‐oxygen coordination complex concomitant with inner sphere electron transfer. The formylglycine generating enzyme (FGE) is an unusual mononuclear copper enzyme that appears to follow a different strategy. Atomic‐resolution crystal structures of the precatalytic complex of FGE demonstrate that this enzyme binds O2 juxtaposed, but not coordinated to the catalytic CuI. Isostructural complexes that contain AgI instead of CuI or nitric oxide instead of O2 confirm that formation of the initial oxygenated complex of FGE does not depend on redox activity. A stepwise mechanism that decouples binding and activation of O2 is unprecedented for metal‐dependent oxidases, but is reminiscent of flavin‐dependent enzymes.

Molecular oxygen (O2) is a sustainable oxidation reagent. O2 is strongly oxidizing but kinetically stable and its final reaction product is water. For these reasons learning how to activate O2 and how to steer its reactivity along desired reaction pathways is a longstanding challenge in chemical research.[1] Activation of ground‐state diradical O2 can occur either via conversion to singlet oxygen or by one‐electron reduction to superoxide. Many enzymes facilitate activation of O2 by direct fomation of a metal‐oxygen coordination complex concomitant with inner sphere electron transfer. The formylglycine generating enzyme (FGE) is an unusual mononuclear copper enzyme that appears to follow a different strategy. Atomic‐resolution crystal structures of the precatalytic complex of FGE demonstrate that this enzyme binds O2 juxtaposed, but not coordinated to the catalytic CuI. Isostructural complexes that contain AgI instead of CuI or nitric oxide instead of O2 confirm that formation of the initial oxygenated complex of FGE does not depend on redox activity. A stepwise mechanism that decouples binding and activation of O2 is unprecedented for metal‐dependent oxidases, but is reminiscent of flavin‐dependent enzymes.

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