Crystallographic characterization and three-dimensional model of yeast Cu,Zn superoxide dismutase

The Cu,Zn superoxide dismutase from yeast was crystallized in the orthorhombic space group P21212 with unit cell dimension a = 105.1 A,b = 142.2 A, c = 62.1 A. The crystals grow in 25 mM citrate, 10 mM phosphate buffer pH 6.5, and 6% (W/V) polyethylene glycol, with a Vm of 3,4 A3/dalton, for two dimers/asymmetric unit. The crystals were unstable in the mother liquor, but were stabilized by transfer to a 35% polyethylene glycol solution. This crystalline form diffracts at high resolution and is suitable for determination of the atomic structure. The three dimensional structure of the yeast enzyme could be model-built by computer graphics techniques using the bovine enzyme atomic coordinates as template. The proposed model requires removal of some salt bridges and non equivalence of the metal-binding sites in the subunits, in line with reported functional properties of the yeast enzyme.