Space Environment Utilization Center, Japan Aerospace Exploration Agency^* Confocal Science Inc.^** MolLogics Inc.^***
○Masaru Sato^* Hiroaki Tanaka^** Koji Inaka^*** Sachiko Takahashi^** Shigeru Sugiyama^*** Mari Yamanaka^** Satoshi Sano^* Moritoshi Motohara^* Tomoyuki Kobayashi^* Tetsuo Tanaka^*

Highly purified alpha-amylase was crystallized using counter-diffusion technique [1,2] in International Space Station for 13 weeks in Japan Aerospace Exploration Agency's project; JAXA-GCF. It diffracted beyond 0.89Å at SPring-8 beamline BL12B2 using polyethylene glycol (PEG) 8000 as a precipitant without forming cluster-like morphology which was usually observed on the ground-based experiment. The numerical analysis suggested that viscosity of the crystallization solution, caused by PEG, might result in growing highly-ordered protein crystals depending on depletion zone formation around a crystal especially under microgravity [3].
Highly purified lysozyme crystallization experiment was performed using NaCl as a precipitant in which PEG 8000 was purposely added to increase viscosity of the crystallization solution for the enhancement of the effects of microgravity. The crystal diffracted beyond 0.88Å was obtained at SPring-8 beamline BL12B2. Some of the protein samples provided by users for JAXA-GCF project improved the crystal quality using the same strategy.
It may be said that highly purification of the sample and enhancement of the microgravity effects by viscous crystallization solution were effective for obtaining atomic resolution crystals. Proper cryoprotectant was also essential for this purpose.
Such an atomic resolution data can provide more precise data of structural features of target proteins. If microgravity experiments are provided more routinely, crystallization in microgravity environment can become one of the options for obtaining high-quality protein crystals.
[1] Garcia-Ruiz, J.M. and Moreno, A., Acta Cryst., D50, 484, 1994
[2] Tanaka, H. et al., J. Synchrotron Rad., 11, 45, 2004
[3] Tanaka, H. et al., Ann. N.Y. Acad. Sci., 1027, 10, 2004