JAXA protein crystallization in space: ongoing improvements for growing high-quality crystals.

The Japan Aerospace Exploration Agency (JAXA) started a high-quality protein crystal growth project, now called JAXA PCG, on the International Space Station (ISS) in 2002. Using the counter-diffusion technique, 14 sessions of experiments have been performed as of 2012 with 580 proteins crystallized in total. Over the course of these experiments, a user-friendly interface framework for high accessibility has been constructed and crystallization techniques improved; devices to maximize the use of the microgravity environment have been designed, resulting in some high-resolution crystal growth. If crystallization conditions were carefully fixed in ground-based experiments, high-quality protein crystals grew in microgravity in many experiments on the ISS, especially when a highly homogeneous protein sample and a viscous crystallization solution were employed. In this article, the current status of JAXA PCG is discussed, and a rational approach to high-quality protein crystal growth in microgravity based on numerical analyses is explained.

Numerical model of protein crystal growth in a diffusive field such as the microgravity environment.

It is said that the microgravity environment positively affects the quality of protein crystal growth. The formation of a protein depletion zone and an impurity depletion zone due to the suppression of convection flow were thought to be the major reasons. In microgravity, the incorporation of molecules into a crystal largely depends on diffusive transport, so the incorporated molecules will be allocated in an orderly manner and the impurity uptake will be suppressed, resulting in highly ordered crystals. Previously, these effects were numerically studied in a steady state using a simplified model and it was determined that the combination of the diffusion coefficient of the protein molecule (D) and the kinetic constant for the protein molecule (ß) could be used as an index of the extent of these depletion zones. In this report, numerical analysis of these depletion zones around a growing crystal in a non-steady (i.e. transient) state is introduced, suggesting that this model may be used for the quantitative analysis of these depletion zones in the microgravity environment.

NASDA aquatic animal experiment facilities for Space Shuttle and ISS.

National Space Development Agency of Japan (NASDA) has developed aquatic animal experiment facilities for NASA Space Shuttle use. Vestibular Function Experiment Unit (VFEU) was firstly designed and developed for physiological research using carp in Spacelab-J (SL-J, STS-47) mission. It was modified as Aquatic Animal Experiment Unit (AAEU) to accommodate small aquatic animals, such as medaka and newt, for second International Microgravity Laboratory (IML-2, STS-65) mission. Then, VFEU was improved to accommodate marine fish and to perform neurobiological experiment for Neurolab (STS-90) and STS-95 missions. We have also developed and used water purification system which was adapted to each facility. Based on these experiences of Space Shuttle missions, we are studying to develop advanced aquatic animal experiment facility for both Space Shuttle and International Space Station (ISS).

Effect of space flight on the frequency of micronuclei and expression of stress-responsive proteins in cultured mammalian cells.

Results of past space experiments suggest that the biological effect of space radiation could be enhanced under microgravity in some cases, especially in insects. To examine if such a synergistic effect of radiation and microgravity also exists in human cells, frequencies of chromosome instability and cellular levels of several stress-responsive proteins were analyzed in cultured human and rodent cells after space flight. Human (MCF7 and AT2KY), mouse (m5S) and hamster (SHE) cell lines were loaded on the Space Shuttle Discovery (STS-95 mission) and grown during a 9-day mission. After landing, the micronuclei resulting from abnormal nuclear division and accumulation of stress-responsive proteins such as p53 and mitogen-activated protein kinases (MAPKs), which are involved in radiation-induced signal transduction cascades, were analyzed. The frequencies of micronuclei in all the four mammalian cell strains tested were not significantly different between flight and ground control samples. Also, the cellular amounts of p53, p21 (WAF1/SDI1/CIP1) and activated (phosphorylated) forms of three distinct MAPKs in MCF7 and m5S cells of flight samples were similar to those of ground control samples. These results indicated that any effect of space radiation, microgravity, or combination of both were not detectable, at least under the present experimental conditions.