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

Abstract

There are two types of homologous enzymes catalysing the dismutation of the superoxide radical--Cu-Zn superoxide dismutases, and manganese or iron superoxide dismutases. In the latter two forms there is a high percentage of identity in the primary structures, and the tertiary structures are very similar particularly in the areas of the active site 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 there is strong metal ion specificity and many enzymes in the family will only be active if the correct metal ion is present. The purpose of this study has been to analyse solved X-ray structures for interactions common in both the manganese and iron forms and those that are specific to each, which may indicate reasons for the metal ion specificity. Initial analysis points to the probability that it is a combination of a number of residues, and not necessarily the same ones in every instance, which confer the specificity. In addition we have identified some anomalies in the currently available Fe/MnSOD structures which may require further remodelling and refinement.