2-Oxoglutarate
(2OG)-dependent dioxygenases catalyze C-H activation while performing a wide
range of chemical transformations. In contrast to their heme analogues,
non-heme iron centers afford greater structural flexibility with important
implications for their diverse catalytic mechanisms. We characterize an <i>in situ</i> structural model of the putative
transient ferric intermediate of 2OG:taurine dioxygenase (TauD) by using a
combination of spectroelectrochemical and semi-empirical computational methods,
demonstrating that the Fe (III/II) transition involves a substantial, fully reversible,
redox-linked conformational change at the
active site. This rearrangement alters the apparent redox potential of the
active site between -127 mV for reduction of the ferric state and 171 mV for
oxidation of the ferrous state of the 2OG-Fe-TauD complex. Structural
perturbations exhibit limited sensitivity to mediator concentrations and
potential pulse duration. Similar changes were observed in the Fe-TauD and taurine-2OG-Fe-TauD
complexes, thus attributing the reorganization to the protein moiety rather
than the cosubstrates. Redox difference infrared spectra indicate a reorganization
of the protein backbone in addition to the involvement of carboxylate and
histidine ligands. Quantitative modeling of the transient redox response using two
alternative reaction schemes across a variety of experimental conditions
strongly supports the proposal for intrinsic protein reorganization as the
origin of the experimental observations.
