Substrate-TriggeredFormation of a Peroxo-Fe 2 (III/III) Intermediate duringFatty Acid Decarboxylation by UndA

The iron-dependent oxidase UndA cleaves one C3–H bond and the C1–C2 bond of dodecanoic acid to produce 1-undecene and CO2. A published x-ray crystal structure showed that UndA has a heme-oxygenase-like fold, thus associating it with a structural superfamily that includes known and postulated nonheme diiron proteins, but revealed only a single iron ion in the active site. Mechanisms proposed for initiation of decarboxylation by cleavage of the C3–H bond using a mono-iron cofactor to activate O2 necessarily invoked unusual or potentially unfeasible steps. Here we present spectroscopic, crystallographic, and biochemical evidence that the cofactor of Pseudomonas fluorescens Pf-5 UndA is, in fact, a diiron cluster and show that binding of the substrate triggers rapid addition of O2 to the Fe2(II/II) cofactor to produce a transient peroxo-Fe2(III/III) intermediate. The observations of a diiron cofactor and substrate-triggered formation of a peroxo-Fe2(III/III) intermediate suggest a small set of possible mechan...