Fact sheet number: FS-2002-2002-84-MSFC
Missions: Expedition 6, ISS Mission 11A, STS-113 Space Shuttle Flight, return flight ULF1, STS-114
Experiment Location on ISS: U.S. Lab EXPRESS Rack No. 4
Principal Investigator: Dr. Daniel C. Carter, New Century Pharmaceuticals, Inc. Huntsville, Ala.
Project Manager: Clark Darty, NASA's Marshall Space Flight Center in Huntsville, Ala.
Structural biology experiments conducted in the Diffusion-controlled Crystallization Apparatus for Microgravity (DCAM) may improve our understanding of the function of important macromolecules and possibly contribute to the development of new therapeutics.
Scientists select macromolecules, crystallize them, and use the crystals to determine the atomic arrangements of atoms within the molecules using intense beams of x-rays or neutrons - a process and field of research known as 'crystallography.' Knowledge gained through crystallography has played a key role in understanding many important chemical and biological processes. The determination of the three-dimensional structures of important proteins and other macromolecules, such as DNA, has contributed significantly over the past 50 years to the scientific understanding of fundamental processes in disciplines ranging from material science to biochemistry and medicine.
Microgravity - the near-weightless condition created as a spacecraft free-falls in orbit around the Earth - has been shown in many cases to produce crystals of improved perfection. This improvement can allow scientists to determine with greater precision the three-dimensional structure of the molecules making up the crystal.
The International Space Station provides for longer-duration experiments in an acceleration-free (no change in the rate of speed, or velocity, of the spacecraft that could affect the experiments), dedicated laboratory, than that provided by the Space Shuttle. Macromolecular crystals require from several days to several months to grow to optimum size. Mission 9A provides for longer-duration experiments in a more research friendly environment. One of the principal objectives of DCAM on the STS-113 mission is to produce extremely large highly ordered crystal specimens specifically for neutron diffraction applications (a more highly specialized subdiscipline of 'crystallography') - a long duration experiment series well suited for the International Space Station.
The Single-locker Thermal Enclosure System (STES) for the structural biology experiment is an incubator/refrigerator module that can house different devices for growing biological crystals in microgravity.
On the Shuttle STS-113 mission to the International Space Station, scheduled for launch in November 2002, the STES unit will house the Diffusion-Controlled Crystallization Apparatus for Microgravity (DCAM). Once on board the International Space Station, the unit will be located in the U.S. Lab EXPRESS Rack No. 4. After an extended growth period of four months, the experiments are scheduled to return to Earth aboard the Shuttle STS-114 mission in March 2003.
The DCAM is designed to grow crystals using the liquid-liquid diffusion method. A total of 81 individual experiments are housed inside the STES in three separate tray assemblies. In each tray, there are 27 reservoirs, each containing a different protein sample. Each device is slightly smaller than a 35mm film canister. The inside of the container is molded into two cylindrical chambers joined by a tunnel. The smaller chamber contains a buffer/precipitant solution. The end cap for this chamber holds the biological sample solution, covered by a semi-permeable membrane. This membrane allows the precipitant solution in the larger chamber to pass into the biological sample solution. A plug filled with porous material separates the two chambers and controls the rate of diffusion. Exposure to the precipitant causes the biological sample to crystallize. Diffusion -- the mixing of the biological sample solution with the precipitant solution -- starts on Earth as soon as the chambers are filled. However, the rate is so slow that no appreciable change occurs before the samples reach orbit one, two -- or even several weeks later.
Protein samples that will be processed during Expedition Six include:
The DCAM has no mechanical system. No crew interaction is necessary except for transferring the PCG-STES unit to the Space Station and back to the Shuttle at the end of the mission.
With science being performed on the International Space Station, scientists are no longer restricted to relatively short-duration flights to conduct structural biology experiments, opening the application of microgravity to a greater selection of important macromolecules. This research will enhance the accuracy of the 3-dimensional structures of specially selected macromolecules, providing improved crystallographic information, which has the potential to impact, a broad base of scientific research on Earth.
Additional information on structural biology crystal growth in microgravity is available at: