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Updated: Mar 18, 2026

Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy
Published on: February 20, 2020
Structural basis for halogenation by iron- and 2-oxo-glutarate-dependent enzyme WelO5
Andrew J Mitchell1, Qin Zhu2, Ailiena O Maggiolo1
1Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, USA.
Abstract:
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. S189A WelO5 produces 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.
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