CRYSTALLOGENESIS STUDIES IN MICROGRAVITY WITH THE ADVANCED PROTEIN CRYSTALLIZATION FACILITY ON SPACEHAB-01

The Advanced Protein Crystallization Facility (APCF), a new protein cr ystallization device developed by ESA for the IML-2 Mission in 1994, w as tested in its maiden Eight on STS-57 Mission in SpaceHab-01 with a physico-chemical experiment on lysozyme crystallization. In pre-flight ground experiments, prior to the Shuttle Mission, the protocol for ly sozyme crystallization with NaCl was based on its solubility diagram a t 18 degrees C and pH 4.5. Crystallization was conducted under microgr avity in 25 APCF reactors using vapor diffusion, dialysis, and free li quid interface diffusion, with control on earth in 25 identical reacto rs. Identical supersaturation values were tested by the three crystall ization techniques. Values of supersaturation derived from ground expe riments allowed for conditions that yielded crystals in microgravity. The average number and size of crystals from the flight experiment and the earth control showed no significant difference; however many crys tals were not free Boating and grew on the walls of some of the protei n chambers. The dialysis technique proved to be suitable, since no add itional nucleation was generated by the membrane. Protein concentratio n measurements indicated that 13 days after activation of the experime nt as much as 70-90% of the protein in supersaturated state had alread y crystallized. Data indicated differences in the crystallization beha vior depending upon the crystallization set-up. Images of the protein chamber of 6 reactors, recorded during the flight, allowed us to evalu ate the early stage of crystallization, to verify that recovered cryst als had actually grown under microgravity conditions, and showed motio ns of crystals during the Mission. Using synchrotron radiation, resolu tion and rocking curve measurements of ground and space lysozyme cryst als grown in APCF reactors showed no significant differences, although the values are much better than previously recorded diffraction limit s and mosaicity data obtained with tetragonal lysozyme crystals grown in other set-ups and under different conditions. All controls foreseen throughout the microgravity experiment proved to be essential for the interpretation of the flight data, as concerning the effect of microg ravity.