The C-terminal substrate-binding domain of the LysR-type transcriptional regulator CynR, contains the type 2 periplasmic binding fold.CynR is a LysR-like transcriptional regulator of the cyn operon, which encodes genes that allow cyanate to be used as a sole source of nitrogen. The operon includes three genes in the following order: cynT (cyanate permease), cynS (cyanase), and cynX (a protein of unknown function). CynR negatively regulates its own expression independently of cyanate. CynR binds to DNA and induces bending of DNA in the presence or absence of cyanate, but the amount of bending is decreased by cyanate. The CynR of LysR-type transcriptional regulator family is composed of two functional domains joined by a linker helix involved in oligomerization: an N-terminal HTH (helix-turn-helix) domain, which is responsible for the DNA-binding specificity, and a C-terminal substrate-binding domain, which is structurally homologous to the type 2 periplasmic binding proteins (PBP2). The PBP2 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.