The C-terminal substrate domain of LysR-type transcriptional regulator AmpR that involved in control of the expression of beta-lactamase gene ampC, contains the type 2 periplasmic binding fold.
AmpR acts as a transcriptional activator by binding to a DNA region immediately upstream of the ampC promoter. In the absence of a beta-lactam inducer, AmpR represses the synthesis of beta-lactamase, whereas expression is induced in the presence of a beta-lactam inducer. The AmpD, AmpG, and AmpR proteins are involved in the induction of AmpC-type beta-lactamase (class C) which produced by enterobacterial strains and many other gram-negative bacilli. The activation of ampC by AmpR requires ampG for induction or high-level expression of AmpC. It is probable that the AmpD and AmpG work together to modulate the ability of AmpR to activate ampC expression. This substrate-binding domain shows 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.