The C-terminal substrate binding domain of LysR-type transcriptional regulators that are involved in the catabolism of dinitrotoluene, naphthalene and gamma-hexachlorohexane; contains the type 2 periplasmic binding fold.
This CD includes LysR-like bacterial transcriptional regulators, DntR, NahR, and LinR, which are involved in the degradation of aromatic compounds. The transcription of the genes encoding enzymes involved in such degradation is regulated and expression of these enzymes is enhanced by inducers, which are either an intermediate in the metabolic pathway or compounds to be degraded. DntR from Burkholderia species controls genes encoding enzymes for oxidative degradation of the nitro-aromatic compound 2,4-dinitrotoluene. The active form of DntR is homotetrameric, consisting of a dimer of dimers. NahR is a salicylate-dependent transcription activator of the nah and sal operons for naphthalene degradation. Salicylic acid is an intermediate of the oxidative degradation of the aromatic ring in soil bacteria. LinR positively regulates expression of the genes (linD and linE) encoding enzymes for gamma-hexachlorocyclohexane (a haloorganic insecticide) degradation. Expression of linD and linE are induced by their substrates, 2,5-dichlorohydroquinone (2,5-DCHQ) and chlorohydroquinone (CHQ). The structural topology of this substrate-binding domain is most similar to that of the type 2 periplasmic binding proteins (PBP2), which are responsible for the uptake of a variety of substrates such as phosphate, sulfate, polysaccharides, lysine/arginine/ornithine, and histidine. The PBP2 bind their ligand in the cleft between these domains in a manner resembling a Venus flytrap. After binding their specific ligand with high affinity, they can interact with a cognate membrane transport complex comprised of two integral membrane domains and two cytoplasmically located ATPase domains. This interaction triggers the ligand translocation across the cytoplasmic membrane energized by ATP hydrolysis.