The rubredoxin from Clostridium pasteurianum: Mutation of the iron cysteinyl ligands to serine. Crystal and molecular structures of oxidized and dithionite-treated forms of the Cys42Ser mutant

Abstract

Isolation is reported of the four mutant proteins of the electron- transfer protein rubredoxin from Clostridium pasteurianum in which each of the four cysteine ligands is changed in turn to serine. They fall into two pairs whose properties depend on whether an interior (C6, C39) or a surface (C9, C42) cysteine ligand is substituted. A crystal structure of the oxidized C42S protein (1.65 Å; R, 18.5%) confirms the presence of an Fen(III)(S(γ)- Cys)3(O(γ)-Ser) center (Fe-O, 1.82(8) Å). Significant structural change is restricted to the region around the mutation. EXAFS experiments confirm Fe(III)S3O (O = O(γ)-Ser or OH(x)) centers in each oxidized protein at pH 8. The reduction potentials of th..