Ligand-binding domain of DNA transcription repressor specific for xylose (XylR)
Ligand-binding domain of DNA transcription repressor specific for xylose (XylR), a member of the LacI-GalR family of bacterial transcription regulators. The ligand-binding domain of XylR is structurally homologous to the periplasmic sugar-binding domain of ABC-type transporters and both domains contain the type I periplasmic binding protein-like fold. The LacI-GalR family repressors are composed of two functional domains: an N-terminal HTH (helix-turn-helix) domain, which is responsible for the DNA-binding specificity, and a C-terminal ligand-binding domain, which is homologous to the type I periplasmic binding proteins. As also observed in the periplasmic binding proteins, the C-terminal domain of the bacterial transcription repressor undergoes a conformational change upon ligand binding which in turn changes the DNA binding affinity of the repressor.