May 1999

New technique should spur research with space-grown protein crystals

Gerry Bunick
Life Sciences Division researcher Gerry Bunick is a space veteran—although he hasn’t been in orbit himself, his experiments have, on both the space shuttle and the space station Mir. NASA has awarded Bunick a grant to develop a process that will be a boon to research with space-grown protein crystals, which have been the subject of his experiments with NASA.

Space is an increasing realm of opportunity for scientists. ORNL, Energy Systems and the American Museum of Science and Energy celebrated Space Day, a national day of recognition for the nation’s accomplishments in space, on May 6. Presenters at the museum included the Engineering Technology Division’s George Wrenn, who described new space launch systems that are in the planning stages. Oak Ridge scientists are involved in the development of some of those new technologies.

Bunick’s work with crystals involves more established technologies, such as the space shuttle, and his latest experiments build on previous work.

In a process Bunick calls “macromolecular crystal annealing,” crystals of biological molecules such as proteins that have been preserved by flash-cooling (rapidly chilled in ultra-cold gaseous or liquid nitrogen) can be returned to room temperature and refrozen in a way that improves them. That’s important when using the crystals in diffraction studies for genetic and other research.

“The crystal’s molecular structure is like a neatly stacked brick wall,” Bunick explains. “When you flash-cool it the stresses can be likened to what an earthquake might do – crack the mortar and disrupt the alignment of the bricks. In crystals stressed by flash-cooling you get an effect called mosaicity that causes smeared X-ray diffraction patterns.”

Crystals grown in space’s microgravity are more perfectly formed than those grown in gravity. Although quick-freezing to preserve them also damages them, Bunick’s process reverses the damage. “Our technique allows the crystal to be brought back to room temperature where the crystal’s “bricks” become realigned and fused together in a process we call annealing. The annealed crystal can then be flash-cooled again without undergoing the level of stress that causes high mosaicity.”

Being able to preserve macromolecular crystals on the space station by first flash-cooling then restoring the crystals to ambient temperature after return to earth is important because researchers cannot use frozen crystals for some experiments. One common experiment involving crystals is heavy-atom soaking, in which atoms are introduced that serve as position markers for diffraction studies. Bunick’s own X-ray diffraction studies with protein crystals have involved nucleosomes, which are the basic building blocks of chromosomes.

“Our process will help improve the data collection quality and success rate in biological X-ray diffraction studies with DOE’s synchrotrons,” Bunick says, adding he expects his experiments to return to space as soon as the International Space Station is operating.   —B.C.