Understanding proteins is basic to understanding the processes of living things. While we know the chemical formulae of proteins, learning the chemical structure of these macromolecules is more di cult. Mapping the three- dimensional structure of proteins, DNA, ribonucleic acid (RNA), carbohydrates, and viruses provides information concerning their functions and behavior. This knowledge is fundamental to the emerging eld of rational drug design, replacing the trial-and-error method of drug development. Microgravity provides a unique environment for growing crystals, an environment that is free of the gravitational properties that can crush the delicate structures of crystals. Currently, several test facilities are used to grow crystals.
The Advanced Protein Crystallization Facility (APCF) can support three crystal- growth methods: liquid-liquid di usion, vapor di usion, and dialysis. Liquid-liquid di usion was not used during Expedition 3. In the vapor di usion method, a crystal forms in a protein solution as a precipitant draws moisture in a surrounding reservoir. In the dialysis method, salt draws moisture away from the protein solution via a membrane separating the two, forming crystals. ESA has announced that due to potential di culties with the vapor di usion method that could cause experiment failure, it will no longer propose the use of this method with the APCF.
APCF-Crystal Growth was one of eight protein crystal investigations that was conducted in the Advanced Protein Crystallization Facility onboard the ISS during Expedition 3.
Iron is an essential trace element that is used by the body to form molecules such as hemoglobin. The structure of the protein ferritin is extremely important to the process of iron storage and release into the body. In order to understand how ferritin helps to maintain the correct amount of iron in the body its structure must be studied in detail. Ferritin also plays an important role in the stable maintenance of the body functions of hematophagous (blood-feeding) insects that are responsible for numerous human deaths worldwide. Understanding ferritin can help in the ght against insects such as the mosquitoes that carry malaria and yellow fever.
Lumazin synthase is a relatively new macromolecule that was created to study crystal movement in microgravity. Its large size accounts for its unique behavior in terms of crystal and solution motion.