The Role of Divalent metal ions as co-repressors for the repressor protein FUR: A study of the Co(II) complexes, Fifth International conference on Bioinorganic Chemistry

Abstract

Metal ions x This work was done in J.B. Neilands' laboratory, Biochemistry Dept.,U.C. Berkeley, California 94720, U.S.A. Ferric wtake regulation (FUR) is a 17 KDa molecular weight repressor protein involved in iron uptake regulation in Escheriechia. m (11. Fur diner binds a 19 bp DNA sequence “i ran box” using Fe1111 ion, invfvo, as corepressor. In vitro, uhen the Fe(IIf concentration reaches a certain level, the Fllr dim&r is activated by complexing to two Fe(I1) ions to forla a fur metal ion complex which binds to the DNA[21. It is established that Co(l!) activates the Fur protein to bind the DNA in vitro[2l. Electronic absorption studies enabled the assignment of a distorted tetrahedral environment arbund the’ Co(I1) ( xnak f 715+ 670, and 530 nr). Equilibrium studies gave evidence of the association of up to 6 Cot II) ions per Fur monomer and presence of a weak site, Kd=600 ~f4, and stronger site Kd=60 UM. The epr parameters (g=1.9, gsh.!3). 6f the Co(IX) fur complex were consistent with the electronic absorption spectra, i,e. both gave evidence of the presence of Co(I1) in a distorted tetrahedral environment. The corpiex of the mutant Fur c92s, c95s, and the C92SC95S with Co(II) helped to characterize the position of ligating sites to the Metal ion on the Fur sequence. The binding of Fur Co(II1 complex to an oligonucleotide representing the “iron box”’ altered the Co(I1) environment indicating an increase in axiaiity. This was evident In epr parameters (g=4.93, g=3,8, and g-1.9). The type of ligands provided by the Fur to the metal ion and the likely role of the retal ion in DNA binding are discussed.