Binding of the ferric uptake regulation repressor protein (Fur) to Mn(II), Fe(II), Co(II), and Cu(II) ions as co-repressors : electronic absorption, equilibrium, and 57Fe Mossbauer studies

Abstract

The binding of the repressor protein (Fur) to Fe(H) as co-repressor was studied. Other transition metal ions such as M&I), Co(B), and Cu(I1) were also studied as models. From the equilibrium studies Kd values of 55,85,36, and 10 PM were obtained for the Fur complex with Fe(II), Mn(II), Co(II), and C&I), respectively. The ratio of metal to Fur monomer was 1:l in both the Fe(II) and M&I) complexes. Fur mutants were also studied. Electronic absorption spectra of the CofII) Fur complex gave evidence of a distorted tetrahedral Co(E) site bound to sulfur. Frozen solution 57Fe Miissbauer spectra of the Fe(B) Fur indicated the presence of Fe(II) in a high spin distorted octahedral environment. The role of the metal ion as co-repressor in the binding of Fur to DNA is discussed in view of the above results.