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An "Exact" Repeat with Small Changes

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An "Exact" Repeat with Small Changes

July 3, 1997 09:30 a.m. CDT

In the pictures below,HiPac video images captures some of the work aboard MSL-1 during the early hours of July 3. The payload crew works at both end of the Spacelab module, a metal sample levitates in TEMPUS, and a water droplet bobbles at the end of its deployment string in preparation for a bubble dynamics test - IFFD.

While the MSL-1 reflight is billed as identical to the original mission plan attempted back in April, a number of small changes were inevitable. Among the differences are variation in the samples flown for the protein crystal growth (PCG) experiments that have become an important "frequent flyer" on Space Shuttle missions.

The PCG experiments cover a range of interests, from basic crystal physics to improving an antibody that fights a lung disease fatal to 3,000 American infants each year.

MSL-1 carries three sets of PCG hardware, the second-generation Vapor Diffusion Apparatus, the Handheld Diffusion Test Cell, and the Protein Crystallization Apparatus for Microgravity (PCAM). The hardware is identical to what MSL-1 carried in April, but as is often the case in science, the specimens have been changed slightly to take advantage of results from the earlier 4 day mission.

work continues on day 2 of STS-94"Despite our early termination, we had one crystal that gave wonderful results," said Dr. Dan Carter, the PCAM principal investigator and the chief executive officer of New Century Pharmaceuticals in Madison, Alabama. The crystal was parvalbumin, a protein involved in the transport of calcium in fish. It is of interest in understanding fundamental biochemistry.

PCAM grows crystals by holding a solution in a small well in a plastic tray. The top of the well is sealed by a rubber gasket until after the apparatus is in orbit; then an astronaut works a crank to ease the gaskets off all the trays in the cylinder. This was done Tuesday afternoon, soon after Columbia started operations in orbit. With the well unsealed, the solution will evaporate and into a reservoir, leaving behind an ever richer solution where a crystal forms because there is no room left for the protein to remain in solution.

While the first MSL-1 flight was intended to fly for 16 days, the scientists studied the samples anyway since the history of science is full of discoveries made in specimens that someone might have thrown out.

In the case of the parvalbumin, Carter said, the investigator, Dr. Jean-Paul Declerq of the University of Louvain in Belgium, found a highly refined crystal that is better than what his instruments can study. Protein crystals are X-rayed to produce patterns that can be decoded to reveal the internal structure. Carter said that Declerq's sample became the first protein to be pushed into the ultrahigh resolution range. Declerq was able to resolve structures down to 0.9 Angstrom, the very edge of what his instruments could do. By comparison, 0.9 Angstrom is about 1/5,000th as long as a single wave of visible light, and several times finer than the best resolution achieved on most other crystals.

At least one other specimen achieved good results on the first MSL-1 flight, Carter said. Dr. John Rosenberg of the University of Pittsburgh achieved better structure and size on crystals of E. coli Gro EL than he did on a longer mission in 1995. E. coli Gro EL is a virus that attacks bacteria, such as the E. coli normally found in the human intestine. Carter said that such studies are fundamental to understanding life processes so we know better how viruses attack any organism.

Even for those who did not get outstanding crystals, some knowledge was gleaned from the first flight.

"You're able to see what improvements you can make in the crystallization process and rapidly incorporate that into your next experiment," he explained. "You see what worked best, and you hope on this one to get an even better result." The changes include subtle variations in the makeup of the protein solution to test variation on the mixture that gave the best results on the previous flight.

Ironically, a couple of investigators are not able to take advantage of the reflight. The Transcription Initiation Factor, which helps start DNA replication, yielded good results, but the protein is so difficult to refine that the German investigators did not have time to make a new batch for the reflight. They are scheduled for a later shuttle mission.

Carter's own samples are reflying. With Intracel, he is investigating the structure of respiratory syncitial virus (RCV) antibody. RCV is a virulent flu-like infection that can sweep through a daycare center in a few days, Carter said. "It's the most serious infant respiratory disease on Earth," he continued, hospitalizing 100,000 babies a year in the U.S., and killing 3,000.

Intracel is testing a therapy based on RCV antibody.

"We are trying to gain an improvement in the protein crystal structure to improve our understanding of its design," Carter said, "to get details of how the antibody attaches to the virus."


For the next 14 days, you can follow along and learn about the science being performed on the mission through activities on this WWW site, as well as the "Liftoff" Mission Home Page, and the Shuttle Web Site.

 


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