The C-terminal substrate binding domain of LysR-type transcriptional activator of the nhaA gene, encoding Na+/H+ antiporter, contains the type 2 periplasmic binding fold.NhaR is a positive regulator of the LysR family and is known to be an activator of the nhaA gene encoding a Na(+)/H(+) antiporter. In Escherichia coli, NhaA is the vital antiporter that protects against high sodium stress, and it is essential for growth in high sodium levels, while NhaB becomes essential only if NhaA is not available. The nhaA gene of nhaAR operon is induced by monovalent cations. The nhaR of the operon activates nhaAR, as well as the osmC transcription which is induced at elevated osmolarity. OsmC is transcribed from the two overlapping promoters (osmCp1 and osmP2) and that NhaR is shown to activate only the expression of osmCp1. NhaR also activates the transcription of the pgaABCD operon which is required for production of the biofilm adhesion, poly-beta-1,6-N-acetyl-d-glucosamine (PGA) .Thus, it is suggested that NhaR has an extended role in promoting bacterial survival. 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.