Crystallization and Preliminary X-Ray Diffraction Studies of a Psychrophilic Iron Superoxide Dismutase from Pseudoalteromonas haloplanktis

The Antarctic eubacterium Pseudoalteromonas haloplanktis (Ph) produces a cold-active iron superoxide dismutase (SOD). PhSOD is a homodimeric enzyme, that displays a high catalytic activity even at low temperature. Using hanging-drop vapour-diffusion technique, PhSOD has been successfully crystallized in two different crystal forms. Both crystal forms are monoclinic with space group P21 and diffract to 2.1 Å resolution. Form I has unit-cell parameters a=45.49Å b=103.63Å c=50.37Å β=108.2° and contains a homodimer in the asymmetric unit. Form II has unit-cell parameters a=50.48Å b=103.78Å c=90.25Å β=103.8° and an asymmetric unit containing two PhSOD homodimers. Structure determination has been achieved using molecular replacement. The crystallographic study of this cold-adapted enzyme could contribute to the understanding of the molecular mechanisms of cold-adaptation and of the high catalytic efficiency at low temperature.