Improved three-dimensional growth of manganese superoxide dismutase crystals on the International Space Station

Manganese superoxide dismutase was crystallized in microgravity with 35 PCAM experiments (Protein Crystallization Apparatus for Microgravity) on the ISS (International Space Station) from 5 December 2001 to 19 April 2002. Crystals were very large in size and could easily be seen by eye. Crystals with 0.45 × 0.45 mm cross-sections and of up to 3 mm in length were obtained in several drops: an 80-fold increase in crystal volume compared with the largest earth-grown crystal. A smaller crystal (0.15 × 0.30 mm in cross-section and 1.6 mm in length) was soaked in cryoprotectant and placed in a cryoloop. Diffraction data were collected at 100 K at the BioCARS bending-magnet beamline. The space group was C222₁, with unit-cell parameters a = 100.64, b = 107.78, c = 179.82 Å. Diffraction spots to 1.26 Å resolution were observed. Unfortunately, the high-resolution diffraction degraded owing to radiation damage and the resolution limit for the complete data set was 1.35 Å. It is anticipated that increasing the crystal volume and diffraction limit through microgravity crystal growth will enable several types of technically challenging structure determinations.