Figure 3. Metal ion-binding sites and binding affinities of Fur mutants.

(a) Coordination of the metal ion-binding sites S1 and S2. Colour code is the same as in Fig. 2. (b) Calorimetric titration of WT Fur (60 μM) with MnCl₂ (2 mM). Data were fitted to a two-binding-site model. Calorimetric titration of the other Fur mutants at S1 or S2 was also performed and was fitted to the one-binding-site model. (c) Binding of WT or mutant Fur protein (2 μM) to the feoAB1 operator determined by SPR. (d) Binding affinities of Fur proteins to metal ion and the feoAB1 operator determined by ITC and SPR, respectively.