Development of a bacterial biosensor for nitrotoluenes: The crystal structure of the transcriptional regulator DntR

The transcriptional regulator DntR, a member of the LysR family, is a central element in a prototype bacterial cell-based biosensor for the detection of hazardous contamination of soil and groundwater by dinitrotoluenes. To optimise the sensitivity of the biosensor for such compounds we have chosen a rational design of the inducer-binding cavity based on knowledge of the three-dimensional structure of DntR. We report two crystal structures of DntR with acetate (resolution 2.6 Angstrom) and thiocyanate (resolution 2.3 Angstrom), respectively, occupying the inducer-binding cavity. These structures allow for the construction of models of DntR in complex with salicylate (K-d congruent to 4 muM) and 2,4-dinitrotoluene that provide a basis for the design of mutant DntR with enhanced specificity for dinitrotoluenes. In both crystal structures DntR crystallises as a homodimer with a head-to-tail arrangement of monomers in the asymmetric unit. Analysis of the crystal structure has allowed the building of a full-length model of DntR in its biologically active homotetrameric form consisting of two head-to-head dimers. The implications of this model for the mechanism of transcription regulation by LysR proteins are discussed. (C) 2004 Elsevier Ltd. All rights reserved.