August 15, 1997

The same material that keeps babies dry is helping to grow crystals of proteins involved in a respiratory disease that attacks the lungs of babies and children.

As the STS-85 mission draws to a close, several hundred protein solution samples should be forming large, well-ordered crystals in the Protein Crystallization Apparatus for Microgravity (PCAM). PCAM, developed in the Space Sciences Laboratory at NASA's Marshall Space Flight Center, is a low-cost device that allows scientists to grow large quantities of crystals aboard the shuttle with little intervention from the astronaut crew.

One of the most basic methods of growing any kind of crystal is to dissolve a material in a solution, then raise the concentration of the material so it can no longer stay dissolved. The molecules bump into each other and link to form a repeating pattern - a crystal (such as the parvalbumin, above, grown by PCAM on STS-94 in July).

Many of us have done this with sugar dissolved in water to make rock candy, giant sugar crystals.

Proteins are much larger - about 2,000 times heavier - and more fragile than sugar, and thus are more difficult to grow as perfect crystals suitable for X-ray studies that reveal their blueprint. These blueprints, in turn, let biochemists work toward treatments for diseases by understanding how bacteria, viruses, cells and drugs work.

PCAM is a small plastic tray (left) molded to provide seven sample cells - a well (a little bigger than a BB) surrounded by a small moat (called a reservoir). The protein solution is placed in the well, and the moat is filled with absorbent material similar to what is used in diapers. Nine PCAM trays are stacked inside a cylinder with synthetic rubber gaskets atop each tray. Until the Shuttle arrives in orbit, plungers press the gasket down to seal the sample in place. In orbit, an astronaut cranks each cylinder to release the gasket so the protein solution can evaporate and be absorbed by the "diaper" in the moat. Near the end of the mission, the astronaut cranks the cylinders again to reseal the samples until they are returned to Marshall for study.

This is the fifth flight for PCAM. STS-85 carries 10 cylinders containing 630 samples. Six cylinders are in a locker to maintain temperature at 22 degrees C (72 degrees F); the other four are in a locker at cabin temperature.

Specimens carried in the PCAM include include respiratory syncytial antibody (a key factor in a severe lung disease of children), augmenter of liver regeneration (involved in the regrowth of damaged livers), human serum albumin (a key protein which carries chemicals through the bloodstream), human cytomegalovirus assemblin (a factor in CMV replication), human antithrombin III (a blood clotting factor), and neurophysin vasopressin complex (involved in the control of blood pressure).

More details on PCAM are available in a fact sheet prepared by NASA Marshall's Microgravity Research Office.

Author: Dave Dooling
Curator: Bryan Walls
NASA Official: John M. Horack