The C-terminal substrate binding of LysR-type transcriptional regulator IlvY, which activates the expression of ilvC gene that encoding acetohydroxy acid isomeroreductase for the biosynthesis of branched amino acids; contains the type 2 periplasmic binding fold.
In Escherichia coli, IlvY is required for the regulation of ilvC gene expression that encodes acetohydroxy acid isomeroreductase (AHIR), a key enzyme in the biosynthesis of branched-chain amino acids (isoleucine, valine, and leucine). The ilvGMEDA operon genes encode remaining enzyme activities required for the biosynthesis of these amino acids. Activation of ilvC transcription by IlvY requires the additional binding of a co-inducer molecule (either alpha-acetolactate or alpha-acetohydoxybutyrate, the substrates for AHIR) to a preformed complex of IlvY protein-DNA. Like many other LysR-family members, IlvY negatively auto-regulates the transcription of its own divergently transcribed ilvY gene in an inducer-independent manner. 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.