Metal‐Responsive Up‐Regulation of Bifunctional Disulfides for Suppressing Protein Misfolding and Promoting Oxidative Folding

Abstract The stress‐responsive up‐regulation process is a sophisticated biological response to maintain cellular homeostasis. In intracellular anti‐oxidant systems, the expression level of oxidoreductases is up‐regulated under oxidative stress, mitigating oxidative damage on biomolecules and enhancing protein folding capacity. Herein, inspired by the biological system, we developed a synthetic folding promotor whose reactivity is up‐regulated under stress conditions. We conjugated two metal‐binding 1,4,7,11‐tetraazacyclotetradecane (cyclam) ligands and a redox‐active disulfide to obtain cyclam‐SS, whose reactivity can be enhanced under metal‐induced stress. Metal coordination increased the redox potential of cyclam‐SS, activating it as an oxidant. While Cu II ions severely hampered the oxidative folding of substrate polypeptides, cyclam‐SS exhibited bifunctional folding‐promoting properties, i) suppressing Cu II ‐mediated misfolding and aggregation, and ii) harnessing Cu II to enhance oxidative folding. Cyclam‐SS was also useful for disulfide‐bond formation to promote oxidative folding of pharmaceutical and pathological proteins, as demonstrated with proinsulin and superoxide dismutase 1 (SOD1). Furthermore, cyclam‐SS protected cultured cells from copper‐induced stress. Thus, we demonstrated the induction of the stress‐responsive up‐regulation process by a bifunctional folding promotor controlling the folding status of biologically important proteins under metal‐induced stress. The strategy of “stress‐responsive up‐regulation” could aid the development of novel synthetic materials for treating intracellular stress and related disorders.