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-Octarellins was one of eight protein crystal investigations that was conducted in the Advanced Protein Crystallization Facility onboard the ISS during Expedition 3. Octarellin
proteins are synthetic that were created so that scientists could easily visualize the proper three dimensional binding site of the a/b-barrel sca old structure (a- helix barrel constructed around a b-sheet barrel). The correct three-dimensional structure must rst be determined in order to design the next generation of increasingly complex octarellins. A large number of disciplines have the potential to bene t from the study and application of arti cially produced octarellins. In the medical eld, for example, the a/b-barrel sca old of octarellins is a perfect structure to which therapeutic peptides (any various natural or synthetic compounds containing two or more amino acids linked by the carboxyl group [the COOH group, typical of all organic acids] of one amino acid and the amino group of another) can be fused.