An analysis of structural similarity in the iron and manganese superoxide dismutases based on known structures and sequences

There are two types of homologous enzymes catalysing the dismutationof the superoxide radical – Cu–Zn superoxide dismutases, and manganese oriron superoxide dismutases. In the latter two forms there is a highpercentage of identity in the primary structures, and the tertiarystructures are very similar particu-larly in the areas of the activesite and in the residues responsible for the formation of the dimer.The quaternary structure of the dimer is also highly conserved.However, it has been found that despite this conservation thereis strong metal ion specificity and many enzymes in the familywill only be active if the correct metal ion is present. The purposeof this study has been to analyse solved X-ray structures forinter-actions common in both the manganese and iron forms andthose that are specific to each, which may indi-cate reasonsfor the metal ion specificity. Initial analysis points to theprobability that it is a combination of a number of residues,and not necessarily the same ones in every instance, which conferthe specificity. In addition we have identified some anomalies inthe currently available Fe/MnSOD structures which may require furtherremodelling and refinement. © Rapid Science 1998