DntR

DntR is a transcriptional regulator protein that controls the expression of genes involved in the biodegradation of dinitrotoluene (DNT) in various Gram‑negative bacteria. It is typically encoded upstream of the dnt operon, which contains genes that convert DNT to catechol and further into central metabolites. DntR belongs to the LysR-type transcriptional regulator family; its primary structure consists of an N‑terminal helix‑turn‑helix DNA‑binding domain and a C‑terminal effector‑binding domain. The protein functions as a homodimer, and dimerization is essential for stable binding to the promoter region of the dnt operon.

The regulator is activated by binding of DNT or one of its metabolic intermediates, often 2,4‑dichlorophenoxyacetyl‑acetate in some species. Binding of the effector induces a conformational change that enhances DNA affinity, thereby promoting recruitment of the RNA polymerase holoenzyme. In the absence of the ligand, DntR has a lower affinity for the operator sequence and acts as a weak repressor or activator depending on the cellular context. Mutagenesis analyses have identified critical residues in the effector‑binding pocket that are essential for sensing the nitroaromatic compound. Knockout strains lacking dntR are unable to grow on DNT as the sole carbon source, whereas overexpression of DntR increases the rate of DNT catabolism.

Because DntR directly links environmental detection of a toxic compound to catabolic gene expression, it has been studied as a potential biosensor element in engineered bacterial strains for bioremediation. Its promoter‑binding specificity also makes it a useful tool for synthetic biology applications that require inducible gene expression in response to nitroaromatic pollutants.