The Protein Crystallization Apparatus for Microgravity (PCAM) is one facility for growing protein crystals on STS-95. The facility uses vapor-diffusion to grow protein crystals, a process in which the liquid in a protein solution is allowed to evaporate, thereby increasing protein concentration and triggering crystallization. Individual protein samples are carried in trays, with seven samples per tray and nine stackable trays contained in each PCAM cylinder. The Single Locker Thermal Enclosure System (STES) accommodates six cylinders, for a total of 378 experiments in a single space shuttle locker. The PCAM's high sample density and the ease with which samples can be prepared and distributed postflight meet NASA's requirement for cost-effective research and satisfy a co-investigator's need for quick turnaround between flight experiments.
Candidate proteins for flight experiments in the PCAM are selected based on proposals submitted to the principal investigator and represent an international group of scientists from industry, academia, and government laboratories. Several of the proposed proteins for flight on STS-95 have been flown before, yielding important results. A sampling of these proteins includes the following:
Pike Parvalbumin are found in the muscles, endocrine glands, skin cells, and some neutrons of vertebrates, but the role they play in the muscles is not yet understood. Researchers are exploring theories of a connection between parvalbumin levels and the speed at which mammals' muscles contract and relax. An ultra-high resolution of parvalbumin structure was achieved from samples grown on STS-83. During STS-94, PCAM produced the largest crystals of pike parvalbumin grown to date.
Respiratory Syncytial Virus (RSV) is an infection that attacks respiratory airways and lungs. Each year, nearly four million U.S. children ages 1 to 5 are infected. Approximately 100,000 of these children require hospitalization, and 4,000 die annually from resulting infection. Crystals of the neutralizing antibody against RSV grown during the STS-85 mission in August 1997 were larger and of higher quality than those grown in previous studies, an encouraging step in the fight against this affliction.
Eco RI Endonuclease-DNA Complex leaves a "trail" that scientists can follow, telling them the specific DNA sites where the protein has attached itself. Research on this complex substance is important for understanding how proteins recognize and target specific sequences of DNA. Researchers hope to discover how proteins discriminate between different DNA sequences that are very similar. Crystals of eco RI produced during STS-85 provided the first high-resolution structural blueprint of this protein.
A variety of other proteins are being considered for flight on STS-95, including lysozyme, albumin, E. coli gro EL, mycobacterium L5 gp 71 repressor, CFA1 pilin, bacteriophage PRD1, ferritin/apoferritin, augmenter of liver regeneration, T7 RNA polymerase, Neurophysin II/Vasopressin complex, hemoglobin C, and pollen allergen.
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