Insight into the mechanism of an iron dioxygenase by resolution of steps following the FeIV=O species

Iron oxygenases generate elusive transient oxygen species to catalyze substrate oxygenation in a wide range of metabolic processes. Here we resolve the reaction sequence and structures of such intermediates for the archetypal non-heme Fe-II and alpha-ketoglutarate-dependent dioxygenase TauD. Time-resolved Raman spectra of the initial species with (OO)-O-16-O-18 oxygen unequivocally establish the Fe-IV=O structure. H-1/H-2 substitution reveals direct interaction between the oxo group and the C1 proton of substrate taurine. Two new transient species were resolved following Fe-IV=O; one is assigned to the nu(FeO) mode of an Fe-III-O(H) species, and a second is likely to arise from the vibration of a metal-coordinated oxygenated product, such as Fe-II-O-C-1 or Fe-II-OOCR. These results provide direct insight into the mechanism of substrate oxygenation and suggest an alternative to the hydroxyl radical rebinding paradigm.