Redox-Dependent Isoforms of the Bacillus cereus Fur Protein: Identification, Structural and Functional Analysis

The synthesis of hemolytic toxins in Bacillus cereus, particularly hemolysin HlyII, is controlled by the Fur protein (BcFur), a metal-sensitive regulator of iron metabolism that activity depends on the redox conditions of the environment. Using LC-MS/MS technology, we detected two BcFur isoforms with different electrophoretic mobilities. The structural and functional differences between these isoforms were determined. A more than 10-fold increase in the binding constant of the BcFur protein to its operator in the presence of 2-mercaptoethanol was revealed. The increased binding activity of BcFur with its operator is due to the presence of free SH groups in Cys residues. This protein functions as a dimer that forms independently of the substrate DNA presence Furthermore, crystals of BcFur were obtained, and the 3D structure of BcFur was resolved. Despite the high similarity of the primary and tertiary structures of BcFur to those of the B. subtilis oxidative stress regulator PerR (BsPerR), their redox sensitivity mechanisms differ. Inactivation DNA-binding of BcFur activity has been shown to occur as a result of oxidation of the Cys residues of the zinc finger, at least under in vitro conditions.