The C-terminal substsrate binding domain of NodD family of LysR-type transcriptional regulators that regulates the expression of nodulation (nod) genes; contains the type 2 periplasmic binding fold.
The nodulation (nod) genes in soil bacteria play important roles in the development of nodules. nod genes are involved in synthesis of Nod factors that are required for bacterial entry into root hairs. Thirteen nod genes have been identified and are classified into five transcription units: nodD, nodABCIJ, nodFEL, nodMNT, and nodO. NodD is negatively auto-regulates its own expression of nodD gene, while other nod genes are inducible and positively regulated by NodD in the presence of flavonoids released by plant roots. 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.