The substrate binding domain of LysR-type transcriptional regulator MleR which required for malolactic fermentation, contains type 2 periplasmic binidning fold.
MleR, a transcription activator of malolactic fermentation system, is found in gram-positive bacteria and belongs to the lysR family of bacterial transcriptional regulators. The mleR gene is required for the expression and induction of malolactic fermentation. 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.