Comparison of protein-water interactions in psychrophilic, mesophilic, and thermophilic Fe-SOD

Iron superoxide dismutase (Fe-SOD) can eliminate superoxide anion radicals and is widely used in pharmaceuticals, cosmetics and foodstuff. It's significant to determine the factors that influence Fe-SOD thermostability. Previous studies have focused on the relationship between the structural parameters and thermostability of Fe-SOD while the contribution of water molecules was overlooked. In this study, we examined the relationship between hydration waters and Fe-SOD thermostability. The Voronoi polyhedra method was used to explore the distribution of hydration waters around the Fe-SODs and it was interesting to find that the distribution of hydration waters is related to the B-factor of amino acids, i.e., the flexibility of residues can affect the distribution of waters. Protein-water and water-water hydrogen bonds were examined. We found that the hydrogen bond density in thermophilic Fe-SOD was higher than that in mesophilic Fe- SOD. In addition, larger hydrogen bond networks that involve more waters covered the thermophilic Fe-SOD.