Crystallization and preliminary X-ray diffraction studies of the iron superoxide dismutase from the eukaryote Vigna unguiculata

Superoxide dismutases are a family of metalloenzymes that catalyze the dismutation of superoxide radicals into molecular oxygen and hydrogen peroxide, and thus represent a primary line of defence against oxidative stress. The iron-containing superoxide dismutases are only found in prokaryotes and plants. The iron superoxide dismutase of Vigna unguiculata (cowpea) consists of two polypeptides of 27 kDa, each binding an iron atom as cofactor. The protein was cloned, overexpressed in Escherichia coli, and purified. After several refined screenings, crystals suitable for X-ray diffraction analysis were obtained. The crystals belong to the monoclinic space group C2, with unit cell parameters a=82.54 Å, b=48.41 Å, c=64.28 Å , ==90o, =119.66o, and contain one molecule per asymmetric unit. At cryogenic temperatures the crystals diffracted to a resolution limit of 1.80 Å using synchrotron radiation at the European Synchrotron Radiation Facility.