Rational De Novo Design of a Cu Metalloenzyme for Superoxide Dismutation

Superoxide dismutases (SODs) are highly efficient enzymes for superoxide dismutation and the first line of defense against oxidative stress. These metalloproteins contain a redox-active metal ion in their active site (Mn, Cu, Fe, Ni) with a tightly controlled reduction potential found in a close range around the optimal value of 0.36 V versus the normal hydrogen electrode (NHE). Rationally designed proteins with well-defined three-dimensional structures offer new opportunities for obtaining functional SOD mimics. Here, we explore four different copper-binding scaffolds: H-3 (His(3)), H-4 (His(4)), H2DH (His(3)Asp with two His and one Asp in the same plane) and H3D (His(3)Asp with three His in the same plane) by using the scaffold of the de novo protein GR alpha D-3. EPR and XAS analysis of the resulting copper complexes demonstrates that they are good Cu-II-bound structural mimics of Cu-only SODs. Furthermore, all the complexes exhibit SOD activity, though three orders of magnitude slower than the native enzyme, making them the first de novo copper SOD mimics.