Structure of Cu/Zn superoxide dismutase from the heavy-metal-tolerant yeast Cryptococcus liquefaciens strain N6

The deep-sea yeast Cryptococcus liquefaciens strain N6 shows high tolerance towards heavy metals, and can grow in the presence of high concentrations of copper ions. Enzymatic analysis indicated that copper ions induced the Cu/Zn superoxide dismutase activity of strain N6 (Cl-SOD1). In this study, the 1.2 Å resolution crystal structure of Cl-SOD1 has revealed several significant residue substitutions compared to the other Cu/Zn SODs. In the electrostatic loop, notably, His135 and Pro136 replace the well-conserved linear residues, while Thr133 substitutes a highly conserved glycine. The electrostatic loop has been shown to be involved in the copper uptake process, and these substitutions have caused an inward dragging of the turn region of the loop. As the introduction of proline and abolishment of glycine decrease loop flexibility, this structural reorganization may have helped stabilize the loop conformation, possibly resulting in more efficient copper uptake and a more stabilized copper-bound form.