Rationally Grafting A Synthetic Multinuclear Metal Center into a Cytokine: A Dual-Functional Designer Metalloenzyme

A designer enzyme consisting of an abiological molecule incorporated into a natural protein has been developed as an exceptionally chemoselective catalyst, highlighting that the internal space of proteins is highly beneficial for enhancing catalytic performance. However, other superior features of proteins have received less attention in designer enzymes: e.g., their use as ligands to construct abiological (multinuclear) metal centers and an intrinsic protein function that has often been traded off for a new function. Here, grafting a synthetic trinuclear zinc complex inside a human cytokine macrophage migration inhibitory factor (MIF) scaffold using solely amino-acid side chains led to a designer multi-metalloenzyme with extrinsic and intrinsic functions. The crystal structure of the designer tri-zinc enzyme verified the high accuracy of our design process based on geometry optimizations and quantum-chemical calculations. The extrinsic catalytic performance of this designer enzyme is of the highest class and comparable to that of previously reported designer zinc hydrolases. Importantly, an intrinsic function of MIF, i.e., its tautomerase activity, was maintained in this designer tri-zinc enzyme. Considering that cytokines are originally expressed in response to in vivo events, this cytokine-based designer metalloenzyme shows promising potential as a synthetic biological tool for the self-adaptive regulation of life phenomena.