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Spectroscopic evidence for a high-spin Br-Fe(IV)-oxo intermediate in the alpha-ketoglutarate-dependent halogenase CytC3 from Streptomyces.

The complex of the mononuclear non-heme halogenase CytC3 from Streptomyces, Fe(II), α-ketoglutarate, bromide, and the substrate l-2-aminobutyryl-S-CytC2 reacts with O2 to form a reaction intermediate. Variable-field, freeze-quench Mossbauer spectroscopy reveals this intermediate to be a mixture of two high-spin Fe(IV) complexes in an approximate 3.7/1 ratio. Freeze-quench Fe K-edge X-ray absorption spectroscopy provides further insight into the structure of this intermediate. A short 1.62-A interaction between the Fe and one of its ligands is attributed to the Fe(IV)-oxo group, and a 2.43-A interaction is assigned to the Fe−Br interaction. A significantly longer Fe−Br separation (2.53 A) is observed in the reactant complex, consistent with lower valency of the Fe in the reactant complex. This intermediate is the first example for a Br−Fe(IV)-oxo complex in a protein and provides evidence for a unifying mechanism for Fe(II) and α-ketoglutarate-dependent dioxygenases and halogenases.