Biological macromolecules make up the machinery, the instruction set, and the scaffold of life. They are smaller than the wavelength of visible light, thus sophisticated techniques are needed to…

Biological macromolecules make up the machinery, the instruction set, and the scaffold of life. They are smaller than the wavelength of visible light, thus sophisticated techniques are needed to visualize them, and through this process, understand how life works. Structural understanding helps to discern mechanisms; once we understand how the machinery works, we aid, or more commonly impede that machinery through appropriate pharmaceutical design. The principal means to visualize the structure of these macromolecules is x-RAY crystallography, a process that measures the diffraction of x-rays from ordered crystals to calculate the atomic structure. The importance of this process is exemplified in over 12 nobel prizes awarded to discoveries made from biological structures derived by x-RAY crystallography. A limiting element to the process is the availability of high-quality, well-diffracting crystals. Quality is defined as a crystal that provides x-RAY diffraction data of sufficient completeness and detail (resolution) to see the structure and hence understand the biology of the system. Biological macromolecules often take many days to grow crystals. Growth in reduced acceleration (commonly termed microgravity) on an orbiting spacecraft extends the physical quality of macromolecular crystals through a reduction in the mosaic spread (caused by slight misalignments of the molecules in the crystal lattice and used as a measure of long-range order) and an increase in crystal volume. Resolution (a measure of short-range order) is not directly affected by microgravity, but can still benefit with the correct experimental design to exploit the demonstrated improvements in long-range order. Microgravity growth can yield an improved quality crystal; however, not all samples improve from microgravity growth. If we could predict which samples could be improved by crystal growth in microgravity, then the true potential of this medium could be exploited in an efficient manner. IT is our hypothesis that growth rate dispersion could be an indicator of crystals whose quality could be improved in microgravity. Growth rate dispersion is a phenomenon encountered in crystallization where seemingly identical crystals, produced from the same conditions, grow at different rates. We contend that large growth rate dispersion on the ground is indicative of a sample that should be improved by microgravity growth. In the case of inorganic crystals, a decrease in growth rate dispersion is correlated with an increase in physical crystal quality. The dispersion itself is thought to be caused by surface artifacts on the growing crystals that induce lattice imperfections. Gravity enables convective flows to develop in a crystallization solution. These flows are driven by density differences as molecules are depleted from the surrounding solution during nucleation and growth of the crystal. We plan to monitor growth rate dispersion of crystals grown on the ground and in microgravity, to determine if there is a correlation between the physical qualities of the resulting crystals with those measurements. We propose to use molecular biology techniques to alter the crystallization contacts and shift the growth rate dispersion properties of a single protein from low to high to test our predictive hypothesis. Finally we propose to extend the study to a selection of good and poorly diffracting crystals on the ground and confirm that those displaying high-growth rate dispersion on the ground are those that are improved on orbit and generate improved structural data when their quality is exploited.