We are advancing the technology of de novo protein design to access allosteric and cooperative metal ion binding events. We are using the tenets of the Monod-Wyman-Changeaux model of allostery as design principles to construct a protein scaffold capable of binding two different metals in a cooperative fashion. Our goal is to provide a novel synthetic route to the high-fidelity incorporation of multiple distinct cofactors into designed proteins, as found in complex metalloenzymes such as cytochrome c oxidase. Additionally, the use of a metal to control protein topology provides for a novel mechanical switch of nanomolecular dimentions.