The C-terminal substrate binding domain of galactose-binding protein regulator contains the type 2 periplasmic binding fold.Galactose-binding protein regulator (GbpR), a member of the LysR family of bacterial transcriptional regulators, regulates the expression of chromosomal virulence gene chvE. The chvE gene is involved in the uptake of specific sugars, in chemotaxis to these sugars, and in the VirA-VirG two-component signal transduction system. In the presence of an inducing sugar such as L-arabinose, D-fucose, or D-galactose, GbpR activates chvE expression, while in the absence of an inducing sugar, GbpR represses expression. 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.