Structure-activity relationship of a recombinant hybrid Manganese superoxide dismutase of Staphylococcus saprophyticus/S. equorum

Recombinant hybrid Manganese superoxide dismutase from Staphyloccus saphropyticus/S. equorum (rMnSODSeq) exhibits stability at high temperatures. The enzyme occurs as a dimer that dissociates around 52 °C prior to unfolding of the monomer around 64 °C, demonstrating contribution of the dimeric form to stability. Here, structure - activity relationship of rMnSODSeq was evaluated on the basis of its activity and stability in the presence of inhibitors, NaCl, denaturants, detergents, reducing agents, and at different pH values. The activity was evaluated at both 37 °C and 52 °C, which the latter is the temperature for dissociation of the dimer. Dimer to monomer transition coincided with significant decrease in residual activity at 52 °C. However, the activity assay results at 52 °C and 37 °C suggest spontaneous re-association of the monomer into dimer. Intriguingly, various new species with melting temperature (TM) values other than those of the dimer or monomer were observed. These species displayed medium to comparable level of residual activities to the native at 37 °C. This report suggests that dimer to monomer transition may be not the only explanation for activity loss or decrease.