An ensemble of crystallographic models enables the description of novel bromate-oxoanion species trapped within a protein crystal

Only a few protein-oxoanion crystal complexes have been described to date. Here, the structure of a protein soaked in a bromate solution has been determined to a resolution of 1.25 Å and refined to final overall R/R _free values of 18.04/21.3 (isotropic) and 11.25/14.67 (anisotropic). In contrast to the single-model approach, refinement of an ensemble of ten models enabled us to determine variances and statistically evaluate bond-length distances and angles in the oxoanions. In total, nine bromate positions, including two BrO₃^-·HBrO₃ dimer species, have been identified on the basis of the anomalous signal of the Br atoms. For all bromate ions, the main-chain amide atoms of the protein were identified as the dominant binding positions, a useful property in any experimental phase-determination experiment.