The complete amino acid sequence of copper, zinc superoxide dismutase from Saccharomyces cerevisiae

Abstract

The amino acid sequence of the copper zinc superoxide dismutase from Saccharomyces cerevisiae has been determined by automated Edman degradation. Peptides were obtained from cyanogen bromide cleavage, Staphylococcus aureus V8 protease digestion, tryptic and chymotryptic digests of the citraconylated reduced and carboxymethylated enzyme, and by further fragmentation of selected peptides with trypsin. From the alignment of these peptides and the previously published sequence of the first 54 amino terminal residues (24) the complete sequence was deduced by direct sequence identification of all 153 amino acid residues and of all peptide overlaps. The amino acid sequence corresponds to a molecular weight of 15,950 for each of the two identical subunits in the native enzyme. The primary structure of yeast copper, zinc superoxide dismutase is 55% identical with the sequence of the copper, zinc enzyme from bovine erythrocytes. Importantly, all the copper and zinc ligands, six histidine residues and one aspartate residue from the bovine enzyme, are conserved in the yeast enzyme. The high overall sequence homology and conservation of important metal binding active site amino acid residues suggest that the three-dimensional structure and in particular the active site geometry is virtually the same for the bovine and yeast enzyme. In contrast no sequence homology is apparent by comparison with the manganese or iron class of superoxide dismutases indicating that the two classes have not evolved from a common ancestor.