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Shedding new light on the Earth's powerstation

Spacelab mission successfully crystallizes photosynthetic protein

July 27, 1998: A German-research team presented results this month on a novel space shuttle experiment designed to crystallize one of the most important photosynthetic proteins, a natural molecule called Photosytem I, which cascades the conversion of sunlight to energy in plants, green algae and some bacteria. Using otherwise similar crystallizing conditions, the space crystals have shown a nearly 10- to 20-fold larger volume compared to their earth-grown counterparts and according to the researchers, yielded "the best data set thus far obtained from Photosystem I crystals."

One of several stories summarizing results from the 16-day Life and Microgravity Spacelab (LMS; left), which flew June 20-July 7, 1996, aboard Space Shuttle Columbia (STS-78). It featured 40 scientific investigations from 10 countries. Its record development and cost - each about half those of most Spacelab missions - make LMS an example of how future space station missions can control experiments remotely from locations around the globe. LMS results were recently published by NASA (see below). The investigation in this story used the European Space Agency's Advanced Protein Crystallization Facility (right).

Scientists hope to use the space grown crystals to improve the biological understanding of how these molecules work based on detailed knowledge of their shape and exact atomic positions. According to the study, the results of two space missions so far suggest that "comparison of the microgravity to the ground control experiments shows a significant influence of the microgravity on the [crystals'] nucleation rate," or the rate at which new protein initiates the growth of small crystals.

Virtually all the energy available for life on earth is made available through photosynthesis--the process by which trapped energy from sunlight gets converted to oxygen and the source for almost all carbon compounds in living organisms. In total, photosynthetic biomass production is about eight times the total annual world consumption of energy from all sources, including those fuels derived from more ancient biomass like coal, petroleum and natural gas. Plant biologists have long held the view that photosynthesis -- the process by which cells in green plants convert the energy of sunlight into chemical energy and use carbon dioxide to produce sugars -- needs two intermediate light-dependent reactions for successful energy conversion: Photosystem II and Photosystem I.

When photons -- particles of light -- enter a plant cell, their energy is used to power these two sequential light-dependent reactions. In Photosystem II (PSII), the light energy is used to split water, producing oxygen and electrons. In Photosystem I (PSI), the group of proteins used in the space shuttle experiment, these electrons are used to produce compounds that ultimately react with carbon dioxide to produce carbohydrates, lipids, proteins and nucleic acids -- the fundamental components of life. Photosystem I contains at least twelve proteins and 100 chlorophyll pigments.

The Photosystem I protein, sometimes called the earth's "power station protein," was analyzed by a scientific team, representing the Max Volmer Institute for Biophysical Chemistry and Biochemistry in Berlin, Germany, who reported their results in this month's Final Report published from the space shuttle mission, the Life and Microgravity Spacelab (LMS). The space experiments were performed on membrane proteins found in ancient organisms, formerly called blue-green algae or blue-green bacteria, and now collectively called cyanobacteria.

Information

Principal investigator

Siegfried Lorenz and Volker A. Erdmann Institut für Biochemie, Fachbereich Chemie, Freie Universität Berlin, Otto-Hahn-Bau, Thielallee 63, D-14195 Berlin (Dahlem), FRG

References

Life and Microgravity Sciences (LMS) Space: Final Report, February 1998, NASA Marshall Space Flight Center, Huntsville, AL. compiled, J. P. Downey. NASA CP-1998-206960

Further readings

  • de Lucas, Larry, et al. 1989. Protein crystal growth in Microgravity, Science, 246: 651 (1989)
  • Muhiuddin,I.P., Rigby, S.E.J., Evans, M.C.W. & Heathcote, P. in "Photosynthesis: from Light to Biosphere" (P.Mathis ed.) II, 159-162 (1995).

As a family, these organisms can be considered the 'grass of the sea', forming the fundamental basis of the entire marine food web. These early ancestors of more modern cell components (called chloroplasts in algae and green plants), were the first oxygenic organisms to convert light to energy on earth. The particular cyanobacterium protein of the space investigation, from the species Synechococcus elongatus, is found abundantly today, representing more than half of the total biomass productivity in all open ocean environments and may process up to 50% of the excess carbon dioxide greenhouse gases implicated in the current global warming debate.

In their controlled study comparing space grown crystals of the molecule with the best data ever previously obtained from Photosystem I crystals formed on earth in a conventional laboratory, they found that the best X-ray data set yet obtained about the molecule's shape was found in the space crystals. This finding moves the investigation closer to revealing the biological function of these complex molecules. According to their report, this is one of the first experiments to produce ground-control crystals in both vertical and horizontal reactors oriented differently with respect to gravity, a procedure "which is not only useful for further microgravity experiments, but may improve the crystallization conditions on earth."

Some estimates suggest that human biology alone depends on the action of nearly half a million different enzymes and proteins, with fewer than 1 in a 100 possessing a known three-dimensional picture of their shape and function. Since 1984 space shuttle experiments to determine novel structures for large, biologically important molecules have compiled results for a host of human diseases ranging from insulin in diabetes to one enzyme called reverse transcriptase that can be blocked in the inhibition of HIV infection. In comparing more than 33 such different biological molecules crystallized on the space shuttle and also in parallel conditions on earth, larger space crystals were observed in 45% of the cases and new space crystal structures in nearly 20% of the cases. In as high as half the space crystals, a 10% or better improvement was seen in the x-ray brightness or its crystallographic resolution needed for determining these large molecules' shape and exact atomic positions.

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