The C-terminal substrate binding domain of LysR-type transcriptional regulator ClcR involved in the chlorocatechol catabolism, contains type 2 periplasmic binding fold.
In soil bacterium Pseudomonas putida, the ortho-pathways of catechol and 3-chlorocatechol are central catabolic pathways that convert aromatic and chloroaromaric compounds to tricarboxylic acid (TCA) cycle intermediates. The 3-chlorocatechol-degradative pathway is encoded by clcABD operon, which requires the divergently transcribed clcR and an intermediate of the pathway, 2-chloromuconate, as an inducer for activation. The 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.