A naturally evolved metal ion transfer mechanism that improves the catalytic performance and stability of superoxide dismutase

Inadequate binding of metal ions is a major cause of low activity and loss of function in metalloenzymes such as superoxide dismutase (SOD). In this study, we report a previously undescribed metal ion transfer mechanism mediated by the metal ion binding domain (MIBD) of SOD, which significantly improves SOD activity and stability. MIBD is mainly found in the N-terminal domain of SOD from Paenibacillus, which evolves under a metal ion deficient environment. MIBD can capture and transfer Fe²⁺ to the conserved functional domain of SOD (SODA) via inter- and intramolecular interactions to maintain and enhance enzymatic activity at different ion concentrations. MIBD also exhibits a similar positive effect on the activity and stability of SOD from other species. Moreover, MIBD does not affect the optimum temperature and optimum pH of SOD, but it increases SOD activity to varying degrees compared with SODA at different temperatures and pHs. This unique MIBD also significantly improves the resistance of SOD to protein denaturants and detergents such as Gdn-HCl, Urea, and SDS, and improves physiological stability of SOD in simulated digestive fluids. This naturally evolved mechanism of SOD provides valuable insights into the design of well-performing metalloenzymes.