Dynamically Controlled Protein Crystal Growth (DCPCG) - 07.29.14
ISS Science for Everyone
Science Objectives for Everyone
Demonstrated significant advances in the ability of researchers to control protein crystal growth processes. Previous research demonstrated that macromolecular crystals grown in microgravity are frequently larger and more perfectly formed than their Earth grown counterparts. Understanding the results obtained from the crystals will lead to advances in manufacturing and biological processes.
Science Results for Everyone
The Dynamically Controlled Protein Crystal Growth (DCPCG) apparatus was designed to control crystal growth by controlling the rate of evaporation. This investigation showed that it worked by growing crystals for test proteins. Investigators determined that the growth could have been better, however, so they tested the apparatus extensively on the ground using a selection of protein solutions: insulin (a hormone that regulates metabolism and use of sugar), serum albumin, and lysozyme (an enzyme that attacks bacteria). The testing showed that a slower evaporation rate yielded better results than a more rapid evaporation rate.
Marshall Space Flight Center, Huntsville, AL, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
ISS Expedition Duration
August 2001 - December 2001
Previous ISS Missions
A variety of protein crystal growth experiments have flown on the Shuttle since 1985 and several have already flown on the ISS. ISS Increment 3 was the first and only space mission for DCPCG.
- DCPCG was the first payload hardware on the International Space Station (ISS) that allowed researchers to control important phases of the crystallization process. Scientists determined which growth methods produced the best quality crystals. High quality protein crystals are necessary for examining the three-dimensional structures of crystals via X-ray diffraction.
- DCPCG hardware was transferred from Shuttle to Station, then activated by the ISS crew. Researchers on the ground controlled all other aspects of DCPCG.
- Data collected from ISS allowed the comparison of growth rates and crystal quality of microgravity versus Earth grown crystals.
Researchers have found that it is easier to grow high quality protein crystals in the weightlessness of low Earth orbit, where gravitational forces will not distort or destroy a crystal's delicate structure. When crystals are returned to Earth, researchers examined their structure by sending X-rays through them and using the resulting data to create computer-based models.
The goal of the DCPCG experiment was to control and improve the crystallization process by dynamically controlling the elements that influence crystal growth. Current growth methods provide little or no control over growth rate and separation of the nucleation and growth phases. The DCPCG system provided researchers real-time control of the diffusion process (supersaturation) through control of the protein concentration. It also determined the differences in vapor diffusion rates (the speed at which the liquid surrounding a protein solution evaporates, leaving behind a protein crystal) between experiments conducted in microgravity and similar experiments conducted on Earth. DCPCG quantified the basic differences between crystal growth on Earth and in space: differences in growth rate, the way crystals moved and organized in the two environments, and allowed researchers to assess in detail the best systems for growing high-quality crystals and how to optimize those systems.
Four different proteins were flown in DCPCG during Expedition 3. These proteins were glucose isomerase (an enzyme that catalyzes the conversion of glucose to fructose), equine serum albumin (a blood plasma protein that is produced in the liver and forms a large proportion of all plasma proteins), VEE capsid (target protein in the development of antiviral drugs to fight Venzuelen equine encephalitis (VEE)), and a chaperone protein that catalyzes the correct folding of newly synthesized proteins. DCPCG consists of a vapor locker (V-locker) that is connected to a Command and Data Management Locker (C-locker) that is installed in ExPRESS Rack 1. The V-locker contained 38 growth chambers surrounded by a closed-loop nitrogen management subsystem. Dry nitrogen flowing through the subsystem caused liquid to evaporate from the growth chambers. An in-line moisture sensor provided feedback as to how much of the liquid had evaporated. A static light-scattering sensor allowed the researchers to modify the rate of evaporation, giving them far more control over the crystal growth process than is afforded by other methods. The C-locker housed the electronics and data ports for the experiment. A large portion of the C-locker is the ancillary equipment area (AEA) drawer, which contains a selection of tools and equipment for the experiment: a CD-ROM, spare flash disks, connector covers, and a tool for activating the experiment hardware.
The crystals that are grown in microgravity are able to grow larger and better organized than on Earth. The research that are done on these crystals may further human space exploration efforts by technological and biological advancements developed as a direct result from this research.
Proteins play a key role in the living world around us. They are the building blocks for humans and other animals and they regulate the biochemical processes of plants. Knowledge of the structure and design of proteins will help researchers design new drugs, combat disease, and improve agricultural products, such as pesticides. Researchers are unlocking this knowledge by studying protein crystals-their growth and three-dimensional atomic structure. For the most part, drugs are not so much discovered anymore, they are designed. Scientists can now target a specific protein of a pathogen, be it bacterial or viral, to maximize a drug's effectiveness while at the same time minimizing possible side effects. This method, known as rational drug design, has one major downside. The exact structure of the target protein must be determined, down to the last molecule. To uncover this molecular structure, scientists use X-ray crystallography. A crystal of the protein is bombarded with X-rays to produce a pattern, which, much like a fingerprint, reveals the identity of the protein's atomic structure. But to get an accurate pattern, the crystal must be as free of imperfections as possible. Growing such crystals can be extremely difficult, even impossible, on Earth because gravity causes the crystals to settle on top of one another resulting in structural flaws.
The DCPCG system demonstrates significant advances in the ability of researchers to gain control of the protein crystal growth process and will provide tremendous opportunities for both terrestrial and microgravity research. Large, high-quality crystals are necessary for the determination of the molecular structure of macromolecules by X-ray diffraction analysis. Previous research has demonstrated that macromolecular crystals grown in microgravity are frequently larger and more perfectly formed than their Earth grown counterparts. This improvement in size and quality translates into X-ray diffraction data of higher resolution and intensity, yielding better structural information about the molecule.
DCPCG required constant power from its EXPRESS Rack. The V-Locker received power from the Shuttle middeck during ascent and descent. The C-Locker did not require power until it was installed on the Station. In addition to data interfaces, DCPCG was equipped with video to provide visual feedback to both Station and ground crew. The V-Locker was filled with dry nitrogen before launch.
Crew transferred the DCPCG hardware from the Shuttle to the ISS, connected the cables between the V-Locker and C-Locker, and activated the experiments. They also periodically checked the equipment to ensure it is operating correctly.
Most DCPCG operations were conducted remotely by crew at the Remote Operations Control Center at the University of Alabama - Birmingham and at the Telescience Support Center at Marshall Space Flight Center. The ground crew was able to change the experiment parameters based on feedback from the in-line moisture sensor and the static light scattering sensor. The Station crew monitored and programed the experiments via the C-Locker, if needed.
DCPCG was the first flight test of an apparatus designed to control the crystal growth process by controlling the rate of evaporation. The apparatus worked on orbit, and crystals were grown for the test proteins; however, the investigators determined that the growth could have been better. The same apparatus was used in extensive testing on the ground. Researchers tested a selection of protein solutions, including insulin (a hormone produced by the pancreas to regulate the metabolism and use of sugar), serum albumin, and lysozyme (an enzyme that attacks bacteria) and found that a slower evaporation rate yielded better results than a more rapid evaporation rate. While the results of the ground tests were published, the DCPCG experiment investigators did not seek to publish any structures from crystals grown in orbit. (Evans et al. 2009)
Ground Based Results Publications
DeLucas LJ. Applications of Protein Crystallography in Structural Biology and Drug Design. 39th Aerospace Sciences Meeting and Exhibit, Reno, NV; 2001
Collingsworth PD, Bray TL, Christopher GK. Crystal growth via computer controlled vapor diffusion. Journal of Crystal Growth. 2000; 219: 283-289.
UAB Center for Biophysical Sciences and Engineering
NASA Fact Sheet
NASA Image: ISS003E8171 - Close-up image of DCPCG hardware, V-Locker and the C-Locker in EXPRESS Rack 1 on ISS Expedition 3.
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Glucose Isomerase crystals from DCPCG on ISS Expedition 3. From left to right, fast evaporation rate, medium evaporation rate and slow evaporation rate.
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Equine Serum Albumin crystals from DCPCG on ISS Expedition 3. From left to right, fast evaporation rate, medium evaporation rate and slow evaporation rate.
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VEE capsid crystals from DCPCG on ISS Expedition 3. From left to right, medium evaporation rate and slow evaporation rate.
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Chaperone protein crystals from DCPCG on ISS Expedition 3. From left to right, medium evaporation rate and slow evaporation rate.
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