Crystal structures of DntR inducer binding domains in complex with salicylate offer insights into the activation of LysR-type transcriptional regulators

Activation of LysR-type transcription factors (LTTRs) is thought to result from conformational changes that occur when inducer molecules bind to their Inducer Binding Domains (IBDs). However, the exact nature of these changes remains to be fully elucidated. We present the crystal structures of two truncated constructs of the LTTR DntR in their apo-forms and in complex with its natural inducer molecule, salicylate. These provide a fuller picture of the conformational changes that can occur in LTTR IBDs and offer insights that may be relevant when considering the mechanism of activation of LTTRs. Two of the crystal structures show that DntR IBDs can bind up to two inducer molecules. The full extent of conformational changes observed is achieved only when inducer molecules are bound in both binding sites identified. Point mutations disrupting the putative secondary binding site produce DntR variants with a reduced response to salicylate in a whole cell system, suggesting that this site is functionally relevant.