The C-terminal substrate binding domain of LysR-type transcriptional regulators involved in benzoate catabolism; contains the type 2 periplasmic binding fold.
This CD includes the C-terminal of LysR-type transcription regulators, BenM, CatM, and CatR, which are involved in the benzoate catabolism. The BenM and CatM are paralogs with overlapping functions. BenM responds synergistically to two effectors, benzoate and cis,cis-muconate, to activate expression of the benABCDE operon which is involved in benzoate catabolism, while CatM responses only to muconate. BenM and CatM share high protein sequence identity and bind to the operator-promoter regions that have similar DNA sequences. In Pseudomonas species, phenolic compounds are converted by different enzymes to central intermediates, such as protocatechuate and catechols. Generally, unsubstituted compounds, such as benzoate, are metabolized by an ortho-cleavage pathway. The catBCA operon encodes three enzymes of the ortho-pathway required for benzoate catabolism: muconate lactonizing enzyme I, muconolactone isomerase, and catechol 1,2-dioxygenase. CatR normally responds to benzoate and cis,cis-muconate, an inducer molecule, to activate transcription of the catBCA operon, whose gene products convert benzoate to catechol. 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. Besides transport proteins, the PBP2 superfamily includes the substrate-binding domains from ionotropic glutamate receptors, LysR-like transcriptional regulators, and unorthodox sensor proteins involved in signal transduction.