The C-terminal substrate binding domain of LysR-like transcriptional regulator CidR, contains the type 2 periplasmic binding fold.
This CD includes the substrate binding domain of CidR which positively up-regulates the expression of cidABC operon in the presence of acetic acid produced by the metabolism of excess glucose. The CidR affects the control of murein hydrolase activity by enhancing cidABC expression in the presence of acetic acid. Thus, up-regulation of cidABC expression results in increased murein hydrolase activity. This substrate binding domain has significant homology to 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.