Enhancing the activity and stability of Mn-superoxide dismutase by one-by-one ligation to catalase.

Dismutation of superoxide by superoxide dismutase (SOD) generates hydrogen peroxide, which may be reduced to hydroxyl radical. The generated H2O2 during the catalysis can have an oxidative damage to SOD. Hydrogen peroxide decomposition by catalase (CAT) can help circumvent the problem. Mn-superoxide dismutase (herein referred to as SOD) and CAT are dimeric and tetrameric proteins, respectively. Herein, through intein-mediated in vivo subunit splicing, the C-terminus of the CAT subunit (CATS) has been specifically ligated to the N-terminus of the SOD subunit (SODS) with a peptide bond. Thus, the splicing product SOD&CAT combines the superoxide anion (•O2-) scavenging ability and the ability of decomposing H2O2. The in vivo subunit splicing has little effect on the secondary structures of the enzymes as confirmed by circular dichroism (CD) spectra. Fluorescence spectra showed that the splicing product SOD&CAT has a higher stability than SOD. In the splicing product SOD&CAT, the SOD subunits are in close proximity to the CAT subunits, facilitating immediate transfer of H2O2 between the enzymes and enabling efficient decomposition of H2O2. SOD&CAT exhibited a superoxide anion (•O2-) scavenging ability 244% higher than that of SOD and 46% higher than that of the mixed enzymes SOD+CAT.