Ambient Diffusion-Controlled Protein Crystal Growth (DCAM)

DCAM Holding Trays DCAM Sample Chamber

Objectives

The objectives of this experiment were to evaluate experiment/hardware approach and produce high quality protein crystals for scientific applications.

Shuttle-Mir Missions
NASA-2 - NASA-5, NASA-7

Approach
DCAM was designed to grow protein crystals by using a liquid-liquid diffusion method. The DCAM experiment used a unique sample container which consists of two chambers separated by a gel fuse. The fuse acts as a diffusion-limited barrier between the two chambers. A precipitating solution, located in one chamber, diffuses through the fuse at a controlled rate (depending on the length of the fuse) and into the protein holding chamber which elicits protein crystallization upon mixing. Sets of three DCAMs are grouped together with interleaving seals. Nine rows are arranged to form a single tray assembly containing 27 individual experiments. Six trays were carried up to Mir on each science increment, making a total of 162 individual experiments per mission. This allowed for the examination of a variety of different types of protein molecules during each mission. DCAM trays were carried up to the Mir Space Station by the Shuttle orbiter. DCAM was a passive experiment with very little crewmember maintenance required. The samples were allowed to grow protein crystals while Mir crewmembers periodically photographed the samples during each science increment. Following each increment, the sample trays were brought back to the ground by the shuttle for postflight x-ray diffraction analysis of the protein crystals.

Results
Exceptionally large crystals of lysozyme (1.25 cm), albumin (0.8 to 1.0 cm), as well as the largest examples of crystals of the nucleosome core particle and histone octamer were produced. Crystals of the membrane associated protein bacteriorhodopsin were of improved size and quality. Additionally, crystals of several proteins have proved suitable for analysis and structure determination by neutron diffraction. This has produced the first completed protein structure determined by neutron diffraction as a direct result of microgravity (J. X. Ho, et al. unpublished results). To date, largely because of limitation in crystal size, only approximately one dozen protein structures have ever been determined by neutron diffraction. Experience gained from flight and ground-based experiments has proven essential to the proper utilization of the technology, as well as successful operations during periods of long-duration microgravity. One consequence of this success is that the technology has been licensed (1) and the hardware is now available commercially for ground-based applications.

Research involving a multi-diciplinary internationally recognized group of scientists has made key strides, both experimentally and theoretically, toward understanding the underlying role of microgravity in production of crystals with improved size and quality (2). A summary of the experiments and results has been published (3). Improved versions of the hardware have been selected through a recent NRA which will pave the way for future experiments on the International Space Station.

DCAM, a specially designed hardware for the Mir experiment series, has proven to be a highly successful and valuable concept for the production of unusually large protein crystals. As a consequence, DCAM appears to have eliminated the barrier to the routine production of macroscopic centimeter sized protein crystals for neutron analysis. Insight into the role of microgravity in protein crystal growth promises to guide future applications.

Earth Benefits
Scientists have discovered that growing some protein crystals in microgravity result in better quality crystals than on the ground. Protein crystals are used in the process for the development of therapeutic drugs. By growing protein crystals in space that cannot be grown on the ground, scientists can develop new drugs to treat diseases.

Publications
D. C. Carter U. S. Patent No. 5,641,681 (1997).

D. C. Carter, K. Lim, J. X. Ho, B. S. Wright, P. D. Twigg, T. Y. Miller, J. Chapman, K. Keeling, J. Ruble, P. G. Vekilov, B.R. Thomas, F. Rosenberger, and A. A. Chernov, "Lower dimer impurity incorporation may result in higher perfection of HEWL crystals grown in microgravity: A case study," J. Cryst. Growth, in press (1998).

D. C. Carter, B. Wright, T. Miller, J. Chapman, P. Twigg, K. Keeling, K. Moody, M. White, J. Click, J. R. Ruble, J. X. Ho, L. Adcock-Downey, G. Bunick, J.Harp, "Diffusion-controlled Crystallization Apparatus for Microgravity (DCAM): Flight and Ground-based Applications," J. Cryst. Growth, in press (1998).

Principal Investigators
Daniel C. Carter, Ph.D.
New Century Pharmaceuticals, Inc.

Co-Investigators
Dr. John Rosenberg
Dr. Mark Wardell
Dr. Gottfried Wagner
Dr. Gerard Bunick
Dr. Franz Rosenberger
Dr. Bill Thomas
Dr. B. C. Wang
Dr. Jean-Paul Declercq
Dr. Louis Delbaere
Dr. Don Frazier
Dr. Bill Stallings

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