Proteins are fundamental components of animal and plant bodies. There are many kinds of proteins with various functions. In order to understand the functions of a protein, and because the functions of proteins are closely related to their structures, it is important to determine its shape (three-dimensional structure) (Figure 1). Although more than a hundred thousand proteins work in our bodies, the structures of many of them have not yet been determined.
Knowledge of the structures of various proteins will lead to a deeper understanding of life phenomena and is necessary to develop pharmaceuticals that activate or inhibit the functions of certain proteins or those based on various actions of proteins. New drugs have already been designed commercially based on the three-dimensional structures of proteins that have been determined.
To analyze the three-dimensional structure of a protein, the protein will be crystallized and then observed with X-rays. The better quality the crystals are, the more precisely the structure can be determined.
When we heat water or use a heater in a room, the water or the air flows up and down. This phenomenon, called thermal convection, occurs when the density of water or air is changed by heat and affected by gravity. It cannot be avoided on Earth. Thermal convection disturbs the molecular arrangement in protein crystals, which are formed when protein molecules are arranged in an orderly fashion. Sedimentation due to gravity can also disturb the arrangement. On the other hand, in the microgravity environment of space, neither thermal convection nor sedimentation occurs; therefore, crystals of better quality with less distortion and disorder (high-quality crystals) can be grown (Figure 2).
Prior to the launch of the Japanese Experimental Module, Kibo, JAXA had conducted protein crystallization experiments in the Russian service module, Zvezda, of the International Space Station (ISS) (Figure 4). Based on these experiments, a technology was established for obtaining high-quality protein crystals by taking advantage of the space environment. Past experiments have indicated that protein crystals obtained in space are of better quality than those obtained on Earth and that they allow more precise structure analyses.
The Protein Crystallization Research Facility (PCRF) onboard Kibo was loaded making good use of these results. Experiments performed using the PCRF provide the following advantages:
(1) The experiments will produce crystals that are better in quality and more order than those obtained on Earth, allowing more detailed structure determination (Figure 2).
(2) The PCRF can hold several crystallization containers (cell cartridges). Since different crystallization conditions can be set for different containers, many crystal growth experiments can be conducted simultaneously, leading to cost reductions (Figure 3).
(3) The process from the receipt of samples to the space experiment to the sample recovery is planned to be completed in 6 to 8 months.
Life sciences are now regarded as important in advancing the technology of Japan. Research for the determination of protein structures and functions is considered particularly important. As part of the research, the Ministry of Education, Culture, Sports, Science and Technology (MEXT) is implementing the Targeted Proteins Research Program and promoting protein research in the areas of Fundamental Biology, Medicine/Pharmacology, and Food/Environment. Experiments conducted in the PCRF taking advantage of the space environment will provide opportunities to produce high-quality crystals necessary for the research. They will also be able to contribute to protein crystallization experiment businesses for drug discovery and research on protein structures and functions by research institutions.
Speedy space experiments are possible.
The process from the JAXA receipt to the in-flight experiment operations will be completed in about 4 months at the shortest (6 to 8 months from sample receipt to sample recovery). Such speedy experiments are suitable for research and development in the industry.
Low-cost space experiments are possible.
JAXA has developed a crystallization cell that can hold about 12 times more varieties of proteins than the existing crystallization cell that has been operating onboard the ISS, at the same capacity. This allows a significant reduction in the cost of space experiments per protein. The advanced crystallization cell that is under development for Kibo would reduce the required amounts of proteins to about one-third; therefore, the device would make it possible to conduct experiments even with proteins that are hard to obtain in large quantities (mainly disease-related proteins).
An example of past results
Yoshihiro Urade, director of the Department of Molecular Behavioral Biology of the Osaka Bioscience Institute, demonstrated in a space experiment for the first time that a new water molecule was involved in reactions of proteins associated with allergic diseases and sleep disorders. He is now working with a pharmaceutical company to develop a drug.
Cooperation with the Japanese government program
In collaboration with the "Targeted Proteins Research Program" by the MEXT, we will try to address major challenges of our society such as the understanding of life phenomena and contribution to medicine and pharmacy.
Research center for applied utilization
Working with the research team led by Professor Atsushi Nakagawa of the Institute for Protein Research, Osaka University, we had conducted space experiments to obtain ultra high-quality crystals in space so that we could determine protein structures at a level where locations of hydrogen atoms are recognized. If protein structures, including the locations of hydrogen atoms, are determined, places that protein drugs fit in (keyholes) can be determined in every detail, and it will be possible to design drugs (keys) with few side effects.
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