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The C-terminal substrate binding domain of LysR-type transcriptional regulator PnbR, which is involved in regulating the pnb genes encoding enzymes for 4-nitrobenzoate catabolism, contains the type 2 periplasmic binding fold. PnbR is the regulator of one or both of the two pnb genes that encoding enzymes for 4-nitrobenzoate catabolism. In Pseudomonas putida strain, pnbA encodes a 4-nitrobenzoate reductase, which is responsible for catalyzing the direct reduction of 4-nitrobenzoate to 4-hydroxylaminobenzoate, and pnbB encodes a 4-hydroxylaminobenzoate lyase, which catalyzes the conversion of 4-hydroxylaminobenzoate to 3, 4-dihydroxybenzoic acid and ammonium. 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. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",