Structure of the effector-binding domain of the arabinose repressor AraR from Bacillus subtilis

In Bacillus subtilis, the arabinose repressor AraR negatively controls the expression of genes in the metabolic pathway of arabinose-containing polysaccharides. The protein is composed of two domains of different phylogenetic origin and function: an N-terminal DNA-binding domain belonging to the GntR family and a C-terminal effector-binding domain that shows similarity to members of the GalR/LacI family. The crystal structure of the C-terminal effector-binding domain of AraR in complex with the effector l-arabinose has been determined at similar to 2.2 angstrom resolution. The l-arabinose binding affinity was characterized by isothermal titration calorimetry and differential scanning fluorimetry; the Kd value was 8.4 +/- 0.4 mu M. The effect of l-arabinose on the protein oligomeric state was investigated in solution and detailed analysis of the similar to crystal identified a dimer organization which is distinctive from that of other members of the GalR/LacI family.