Structural basis for halogenation by iron- and 2-oxo-glutarate-dependent enzyme WelO5

A 2.4-Å-resolution x-ray crystal structure of the carrier-protein independent halogenase, WelO5, in complex with its welwitindolinone precursor substrate, 12-epi-fischerindole U, reveals that the C13 chlorination target is proximal to the anticipated site of the oxo group in a presumptive cis-halo-oxo-iron(IV) (haloferryl) intermediate. Prior study of related halogenases forecasts substrate hydroxylation in this active-site configuration, but x-ray crystallographic verification of C13 halogenation in single crystals mandates that ligand dynamics must reposition the oxygen ligand to enable the observed outcome. Ser189Ala WelO5 effects a mixture of halogenation and hydroxylation products, showing that an outer sphere hydrogen bonding group orchestrates ligand movements to achieve a configuration that promotes halogen transfer.