Expression of bovine adrenodoxin in E. coli and site-directed mutagenesis of /2 Fe-2S/ cluster ligands.

Expression systems for adrenodoxin into the periplasm and the cytoplasm of E. coli have been developed as a prerequisite for site-directed mutagenesis studies. In both systems the /2Fe-2S/ cluster of the protein was correctly assembled, the cytoplasmic one gives, however, a tenfold higher expression level. To determine which of the five cysteines at positions 46, 52, 55, 92, and 95 coordinate the /2Fe-2S/ center, they have been individually mutated into serines. From these mutants, only C95S forms a functionally active holoprotein. Thus, residues 46, 52, 55, and 92 are the cysteines that coordinate the /2Fe-2S/ cluster in adrenodoxin.