The first crystal structure of manganese superoxide dismutase from the genusStaphylococcus

Abstract

A recombinantStaphylococcus equorummanganese superoxide dismutase (MnSOD) with an Asp13Arg substitution displays activity over a wide range of pH, at high temperature and in the presence of chaotropic agents, and retains 50% of its activity after irradiation with UVC for up to 45 min. Interestingly,Bacillus subtilisMnSOD does not have the same stability, despite having a closely similar primary structure and thus presumably also tertiary structure. Here, the crystal structure ofS. equorumMnSOD at 1.4 Å resolution is reported that may explain these differences. The crystal belonged to space groupP3221, with unit-cell parametersa= 57.36,b= 57.36,c= 105.76 Å, and contained one molecule in the asymmetric unit. The symmetry operation indicates that the enzyme has a dimeric structure, as found in nature and inB. subtilisMnSOD. As expected, their overall structures are nearly identical. However, the loop connecting the helical and α/β domains ofS. equorumMnSOD is shorter than that inB. subtilisMnSOD, and adopts a conformation that allows more direct water-mediated hydrogen-bond interactions between the amino-acid side chains of the first and last α-helices in the latter domain. Furthermore,S. equorumMnSOD has a slightly larger buried area compared with the dimer surface area than that inB. subtilisMnSOD, while the residues that form the interaction in the dimer-interface region are highly conserved. Thus, the stability ofS. equorumMnSOD may not originate from the dimeric form alone. Furthermore, an additional water molecule was found in the active site. This allows an alternative geometry for the coordination of the Mn atom in the active site of the apo form. This is the first structure of MnSOD from the genusStaphylococcusand may provide a template for the structural study of other MnSODs from this genus.