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The C-terminal substrate-binding domain of the LysR-type transcriptional regulator OxyR, a member of the type 2 periplasmic binding fold protein superfamily. OxyR senses hydrogen peroxide and is activated through the formation of an intramolecular disulfide bond. The OxyR activation induces the transcription of genes necessary for the bacterial defense against oxidative stress. The OxyR of LysR-type transcriptional regulator family is composed of two functional domains joined by a linker helix involved in oligomerization: an N-terminal HTH (helix-turn-helix) domain, which is responsible for the DNA-binding specificity, and a C-terminal substrate-binding domain, which is structurally homologous to the type 2 periplasmic binding proteins. As also observed in the periplasmic binding proteins, the C-terminal domain of the bacterial transcriptional repressor undergoes a conformational change upon substrate binding which in turn changes the DNA binding affinity of the repressor. The C-terminal domain also contains the redox-active cysteines that mediate the redox-dependent conformational switch. Thus, the interaction between the OxyR-tetramer and DNA is notably different between the oxidized and reduced forms. The structural 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. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",