Crystallographic characterization of recombinant human CuZn superoxide dismutase

Recombinant human CuZn superoxide dismutase as expressed in yeast has been crystallized in three different crystal forms. Hexagonal plates grow from 2.4 M ammonium sulfate, pH 7.5, and belong to the space group P6₃22, with cell dimensions a = b = 113.5(3), c = 151.5(5) Å, and V(m) = 2.21 ų/dalton for two dimers per asymmetric unit. At 2.0 M ammonium sulfate, pH 7.5, chunky wedges grow in space group C222₁, a = 205.2(6), b = 166.5(4), c = 145.4(4) Å with a V(m) of 2.43 ų/dalton for eight dimers per asymmetric unit. With polyethylene glycol 8000, pH 7.5-8.0, hexagonal prisms are obtained with cell dimensions a = b = 197.4(6), c = 43.1(2) Å, space group P6, and V(m) = 2.53 ų/dalton for three dimers per asymmetric unit. All of these forms diffract to high resolution, are stable to x-rays, and appear suitable for determination of the atomic structure. Crystals of the doubly mutated enzyme (Cys⁶ → Ala, Cys¹¹¹ → Ser) grown from both micro- and macroseeds of the wild type protein demonstrate the feasibility of isomorphous crystallization of site-directed mutants of the cloned parent enzyme for comparative structure-function studies.