Crystal structure of yeast Cu,Zn superoxide dismutase. Crystallographic refinement at 2.5 angstrom resolution

The structure of Cu,Zn yeast superoxide dismutase has been determined to 2.5 angtrom resolution. The enzyme crystallizes in the P2 sub(1)2 sub(1)2 space group with two dimeric enzyme molecules per asymmetric unit. A dimeric molecule of the enzyme is composed of two identical subunits related by a non-crystallographic 2-fold axis. Each subunit (153 amino acid residues) has as its structural scaffolding a flattened antiparallel eight-stranded beta -barrel, plus three external loops. The overall three-dimensional structure is quite similar to the phylogenetically distant bovine superoxide dismutase (55% amino acid homology), the largest deviations can be observed in the regions of amino acid insertions. The major insertion site hosting residues Ser25A and Gly25B, occurs in the 2,3 beta -turn between strands 2b and 3c, resulting in the structural perturbations of the two neighbouring strands.