| Abstract
| - A mononuclear iron-sulfur center, capable of reversibleelectron transfer, has been introducedinto thioredoxin, a protein devoid of such sites, using an automated,structure-based design algorithm.One of the sites predicted by the Dezymer computer program tointroduce a tetrahedral tetrathiolate ironcenter included the intrinsic Cys32−Cys35 disulfide of wild-typethioredoxin and two additional mutants,Trp28Cys and Ile75Cys, thereby converting a disulfide into ametal-based redox center. This designedprotein forms a 1:1 monomeric complex with FeIII, whoseelectronic absorption and EPR spectra closelyresemble those of the rubredoxins, as intended. CoIIspectra provided further confirmation of tetrahedraltetrathiolate metal coordination. The designed protein is capableof undergoing successive cycles ofoxidation and reduction. The computer-generated design only tookinto account the geometry of theprimary coordination shell around the metal. We have thereforedemonstrated that simple geometricalconsiderations can be sufficient to reproduce the dominant electronicstructure and reactivity of a simplemetal-based redox center.
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