Engineering a thermostable iron superoxide dismutase based on manganese superoxide dismutase from Thermus thermophilus

Three residues His29, His84 and His171 were found to be the ligands of metal ions of one hyperthermostable Mn-SOD produced by Thermus thermophilus HB27 after multiple sequence alignment. Conversion of these residues might cause a change of metal-binding specificity. Thus, three mutants His29Ala, His84Ala, and His171Ala were prepared. The mutant types changed, and the metal-binding specificities of His29Ala and His171Ala altered from Mn to Fe. The alpha-helix contents of His29Ala and His171Ala were 66% and 59% respectively, suggesting that the mutants folded with a reasonable secondary structure. His29Ala showed an activity comparable to that of the wild type, and His171Ala exhibited a 39.6% higher activity than the wild type. These two mutants were thermostable from 30 to 50 degrees C after incubation for 30 min. The activity of His171Ala retained 51% at 70 degrees C compared with 36.7% for His29Ala. Both mutants retained >80% residual activity in the pH range 5.0-10.0 (except their pI of 8.0) after incubation at 4 degrees C for 30min. This study provides a good foundation for accelerating the development of thermostable Fe-SOD for application in the fields of medicine and cosmetics. (C) 2015 Elsevier Ltd. All rights reserved.