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 Sept
17, 1998: Anyone who has ever fallen
on grass knows that nature has chemicals that are as permanent
as ink. At least one of those chemicals holds promise as an "electronic
ink" that can be used in improved computer displays.
The chemical is bacteriorhodopsin, a purple protein essential
to the cell wall of Halobacterium halobium, a mysterious
resident of salt-marshes and lakes. When nutrients get scarce,
this bacteriorhodopsin becomes a light-converting enzyme that
keeps the organism's life cycle going. It's a protein powerhouse
that in times of famine flips back and forth between purple and
yellow colors. If controllable, this could be valuable in computer
display panels.
At right, above: The now almost-dry lake bed
of Owens Lake, California, shows the pink bloom of halophilic
("salt-loving") bacteria in the muddy brine. Click
on the picture to see several more
views of the halophilic inhabitants of Owens Lake. (photo
courtesy Tony Phillips/Bishopwebworks)
Above: Artist's concept of microorganisms
in the Owens Lake - the image represents a magnification of approximately
2000x. The red coloration of the brine is caused primarlity by
rod-shaped, salt-loving bacteria (Halobacterium). There are also
two or more species of halophilic green algae, one of which,
the Dunaliella, has an intense red form that adds to the
reddish color of the lake bed. All are shown swimming among cuboidal
crystals of sodium chloride (salt). |
In the last 25 years, bacteriorhodopsin
has excited a great deal of interest among biochemists, biophysicists,
and most recently among companies seeking to build battery-conserving,
long-life computer displays. The protein, sometimes called nature's
"electronic ink" was grown in orbit on board the Space
Shuttle for a scientific team from Justus-Liebig University in
Glessen, Germany and the Institute for Physiological Chemistry
in Hamburg.
Part of the attraction to understanding these light powerhouses
is that natural materials often perform very complex functions
that cannot be easily obtained from manufactured materials such
as semiconductors. They have been optimized for these functions
by billions of years of evolution and often perform them better
than any human-designed material could. |
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For example, bacteriorhodopsin is an attractive material for
all-optical 'light' computers because of its two stable protein
forms, one purple and one yellow. Shining two lasers of different
wavelengths alternately on the protein flips it back and forth
between the two colors. Several research groups have already
used bacteriorhodopsin as computer memory and as the light-sensitive
element in artificial retinas.
According to their report, the space crystal
was stabilized under microgravity conditions...
Further experiments in microgravity, as a favorable environment
of improved crystallogenesis, provide additional progress in
the investigation of difficult membrane proteins such as bacteriorhodopsin.
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In nature, this salt-loving, probably ancient, organism undergoes
a light-stimulated cycle of protein rearrangements which can
interact photochemically. This may be much how similar retinal
proteins in the eye allow more evolved organisms to see.
Analyzing them on Earth has been difficult because these kinds
of complex membrane proteins typically require detergents to
make them compatible with biological analysis in water.
The cubic-shaped space crystals showed a nearly 20-fold larger
volume compared to earth-grown counterparts. In comparing space
grown crystals of the bacteriorhodopsin with similar crystals
formed on earth, the team found that a favorable environment
minimizing gravity may advance the search for new means to reveal
the biological function of these complex molecules.
The large volume of the space-grown crystals will help scientists
read the protein's blueprint and understand how it operates.
From this, they hope to develop versions that could be used in
future computers.
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Above: a computer-generated slice of a larger
image (632x490 pixels; 74KB) of the bacteriorhodopsin protein
from the Brookhaven National Labs Protein Database. |
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Information |
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Principal investigator: Torsten Rothaermel, Gottgried Wagner, Justus-Liebig
University, Dept. Biology, Senckenbergstrasse 17, 35390 Giessen,
Germany
Co-investigators: Christian
Betzel, Markus Perbandt, Institute of Physiological Chemistry,
c/o DESY, Geb. 22a, Notkestrasse 85, 22603 Hamburg, Germany
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
- Altmuller, D., Grolig, F., Lindhardt, R.,
and Wagner, G.: Bacteriorhodopsin - A Membrane Protein to Convert
Light Energy. In Proceedings of the Norderney Symposium on
Scientific Results of the German Spacelab Mission D1, Norderney,
Germany, August 27-29, 1986, pp. 294-296. (post-flight)
- Cowen, R. Juggling at the speed of light.
Science News 143(Jan. 23, 1993):63.
- de Lucas, Larry, et al. Protein crystal
growth in microgravity, Science, 246: 651 (1989)
- Lewis, A., et al. Optical computation with
negative light intensity with a plastic bacteriorhodopsin film.
Science 275(March 7, 1997):1462.
- Lipkin, R. The eye's photochemistry. Science
News 146(Oct. 29, 1994):279.
- _____. Lighting the way to speedier circuits.
Science News 139(June 22, 1991):389.
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One of several stories summarizing results
from the 16-day Life
and Microgravity Spacelab (LMS), which flew June 20-July
7, 1996, aboard Space Shuttle Columbia (STS-78; left). It featured
40 scientific investigations from 10 countries. Its record development
and cost - each experiment cost about half of most Spacelab experiments
- 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.
Other LMS stories:
- Nature's sugar
high - Spacelab successfully crystallizes
an intensely sweet protein from the African Serendipity Berry
that has 3000 times the kick of table sugar - and no calories.
- Great Bugs of
Fire Spacelab crystallizes a protein
from a very weird, and surprisingly common, volcano-loving bug.
Scientists hope to discover how these organisms can survive in
such extreme conditions.
- Nature's "electronic
ink" Another extremophile - a
bacterium which thrives in high-salt conditions - produces a
fascinating protein which changes color extremely efficiently.
Crystals from Spacelab make scientists hopeful that they can
understand the biological function and apply it to, for example,
artificial retinas for people. (this story)
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Biotechnology in space
Some estimates suggest that human biology
depends on the action of nearly half a million different enzymes
and proteins. In fewer than 1 case in 100, we have a three-dimensional
picture of shape and function 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 one enzyme called
reverse transcriptase that can be blocked to inhibit HIV infection.
In comparing more than 33 such different biological
molecules crystallized on the Shuttle and also in similar conditions
on earth, space produced larger space crystals in 45% of the
cases and new structures in nearly 20% of the cases. As many
as half the space crystals had a 10% or better improvement in
the x-ray brightness or the crystallographic resolution. Both
are important to determining these large molecules' shape and
exact atomic positions. |
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