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May 10, 1999: Biologists conducting Space Shuttle
experiments may be one step close A German research team recently presented the results of their Space Shuttle experiment designed to crystallize Photosystem I molecules. According to the researchers, "This experiment has yielded the best data set thus far obtained from Photosystem I crystals." Right: Photo credit: Department of Energy, Daniel Peck |
r to shedding light on the biggest power
booster on the planet: a protein in green plants called Photosystem
I.|
During Scientists crystallize protein molecules in order to study their complex internal structures. Because the molecules are too small to study directly under a microscope, scientists use X-ray diffraction to get a picture of the molecule. |
photosynthesis, the cells in green plants undergo
two simultaneous reactions, both of which rely on a separate
kind of protein. Photosystem I protein molecules use the trapped
energy in sunlight to convert carbon dioxide into carbon and
oxygen. This provides the plant food in the form of carbohydrates,
lipids, proteins and nucleic acids - the building blocks of life.
Photosystem II protein molecules use light energy to split water
into hydrogen and oxygen for plant respiration.|
Shining X-rays through a crystal produces a scattering pattern,
which is a type of blueprint. Think of a shadow cast through
a picket fence - the shape of the shadow would tell you that
the fundamental building block of the fence is a rectangular
board. Shining X-rays through a protein crystal indicates the
protein's shape, where it's located, and ultimately how it may
work. High quality crystals - composed of ordered and repeating units of a particular protein - are required for X-ray diffraction. Some of the crystals grown in the microgravity conditions of space are more perfectly ordered than crystals grown on Earth. Microgravity can also affect the rate at which the proteins initiate new growth. Space crystals have shown a 10 to 20-fold larger volume compared to the Earth-grown counterparts.
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Left: In the microgravity environment of the
Space Shuttle, scientists have shown some improved capability to
grow macromolecular crystals with a higher degree of order. Using
a process called "X-ray crystallography," they can
map the structure of proteins and advance the fundamental understanding
of how they work. 
The
Photosystem I protein molecule, sometimes called "the Earth's
power station," was analyzed by a scientific team representing
the Max Volmer Institute for Biophysical Chemistry and Biochemistry
in Berlin, Germany. The team reported their results in their
Final Report published from the Life and Microgravity Spacelab
(LMS) mission. The team hopes these results will give scientists
a more detailed knowledge of the Photosystem I molecule's shape,
exact atomic positions, and biological functions. And by using
the results of the experiments on the space shuttle, scientists
can improve the crystallization conditions here on Earth.
The Earth's environments - from forests to  grasslands to the oceans - are direct
products of the Photosystem protein molecules. From the beginning
of life, Photosystem processes in algae completely altered the
atmosphere, transforming the carbon dioxide environment into
an oxygen-rich one. Left: Algae in the early Earth's oceans transformed the atmosphere. Photo credit: Department of Energy, David Parsons. The two Photosystem proteins underlie the Earth's balance between water and heat and between oxygen and carbon dioxide. They ultimately supply the nutrients for almost every living thing on the planet, as well. Most of the organisms on Earth receive their sustenance directly or indirectly from photosynthetic vegetation. Without the Photosystem molecules, life as we know it would cease to exist.
 Burning carbon fuel such as oil and coal produces most of this excess carbon dioxide. This process currently supplies much of the world's power needs, but the fuel reserves are rapidly running out. Nonpolluting alternative fuel sources are being developed to take the place of oil and coal. In the 1970s, solar power - a clean and unlimited power source - seemed to be the most promising alternative. Harnessing the power of the Sun to power the Earth, however, has been plagued with difficulties. To generate a lot of power, you need extremely large solar panels. And what do you do for power when the sun sets? Right: A 210-kilowatt crystalline silicon photovoltaic system provides solar power to Sacramento, Calif. Photo credit: Department of Energy/Sacramento Municipal Utility District. |
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Knowing the Code Many essential biology questions depend on knowing the structure of proteins and enzymes. By charting their shape, scientists can determine how the molecules work. But these molecules may also change shape when performing important functions, like carrying oxygen in blood hemoglobin. In photosynthesis, there are many energy producing conversion steps from sunlight to plant development and growth. Some estimates suggest that human biology depends on the action of nearly half a million different enzymes and proteins. But we only have a three-dimensional picture of shape and function for fewer than 1 in 100 of these complex chemicals. Since 1984, the Space Shuttle has carried experiments to determine the structures of large, biologically important molecules. This research has compiled results for a host of human diseases ranging from insulin for the control of diabetes, to the reverse transcriptase enzyme that, when blocked, inhibits HIV infection. Just as in human cells,  the Photosystem proteins inside a plant
cell are translated from amino acids. Amino acids have a 20 letter
alphabet for each of the 20 naturally occurring amino acids (shown
below as AAs). These amino acids are in turn translated from
the complex array of nucleic acids in DNA (coded as the letters
A,G,T and C). A description of the molecular code reads like
an encrypted message:AAs =FFLLSSSSYY**CC*WLLLLPPPPHHQQRRRRIIIMTTTTNNKKSSRRVVVVAAAADDEEGGGG Starts = ---M---------------M------------MMMM---------------M------------ Base1 = TTTTTTTTTTTTTTTTCCCCCCCCCCCCCCCCAAAAAAAAAAAAAAAAGGGGGGGGGGG GGGGG Base2 = TTTTCCCCAAAAGGGGTTTTCCCCAAAAGGGGTTTTCCCCAAAAGGGGTTTTCCC CAAAAGGGG Base3 = TCAGTCAGTCAGTGTCAGTCAGTCAGTCAGTCAGTCAGTCAGTCAGTCAGT CAGTCAGTCAG... Much work remains to be done in uncovering the shape and detailed way the Photosystem power-converting molecules achieve their efficiency. By using the results from space shuttle experiments, someday we may understand how that transformation happens in detail. Such experiments make possible the study of proteins that had once proved too difficult to dissect at the molecular or atomic size. |
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Life on the Edge Project A good illustration of how photosynthesis leads to environmental balance is the terrarium. A sealed jar of carefully balanced photosynthesizing organisms can sustain themselves for long periods without exposure to outside material nutrients or gases. Such a microbial terrarium can keep its ecological balance nearly indefinitely without any care or maintenance. The secret to this self-sufficiency is that green or purple photosynthesizing organisms generate their own source of life from the energy in light. This ability allows them to divide and multiply in a stable manner. NASA's "Life on the Edge" project tests some of the limits to this remarkable behavior. By closing several green biomass mixtures into sealed jars, these organisms are frozen within a deep freezer to a frigid -80 deg C (-112 deg F), temperatures exceeding the coldest winter weather in Antarctica (-44.5 deg C, or -48 deg F). Afterwards, the jars are thawed and opened, and scientists then grow the organisms in a culture to assess their viability. Healthy growing ecosystems have been revived from this ultimate deep freeze. |
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Other LMS stories:
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This is one of several stories summarizing results
from the 16-day 
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