Predicting the substrate scope of the flavin-dependent halogenase BrvH.

The recently described flavin-dependent halogenase BrvH is able to catalyze both bromination and chlorination of indole, but shows significantly higher bromination activity. BrvH was annotated as a tryptophan halogenase, but does not accept tryptophan as a substrate. Its native substrate remains unknown. A predictive model with the data available for BrvH was analysed. A training set of compounds tested in vitro was docked into the active site of a complete protein model based on the X-ray structure of BrvH. The atoms not resolved experimentally have been modelled using molecular mechanics force fields to obtain this protein model. Furthermore, docking poses for the substrates and known non-substrates have been calculated. Parameters like distance, partial charge, and hybridization state have been analysed to derive rules for prediction of activity. With this model for activity of the BrvH, a virtual screening suggested several structures for potential substrates. Some of the thus preselected compounds were tested in vitro and several could be verified as convertible substrates. Based on information on halogenated natural products, a new dataset was created to specifically search for natural products as substrates/products, and virtual screening in this database yielded further hits.