NSF PR 00-34 - May 18, 2000
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Shedding Light on Luminescence: Scientists Visualize
Structure of the Photoprotein Aequorin
Anyone who's spent time at a beach on a warm summer
night has seen them: luminescing ctenophores that
twinkle like tiny stars in moonlit waters. No one
knows exactly why these comb jellies flicker and glow,
but Marine Biological Laboratory (Cape Cod, Massachusetts)
senior scientist Osamu Shimomura now knows a lot more
about the structure of the remarkable protein that
is not only responsible for this phenomenon, but has
proved to be an invaluable tool for researchers studying
the role of calcium in disease.
In this week's issue of the journal Nature,
Shimomura and his colleagues James Head from Boston
University, Katsunori Teranishi from Mei University
(Japan), and Satoshi Inouye from Chisso Corporation
(Japan), describe the three-dimensional crystal structure
of aequorin, the photoprotein that illuminates jellyfish,
centophores and many other luminescing organisms.
The study was supported by the National Science Foundation.
The work of these investigators has clearly demonstrated
how insights into the structure of a protein lead
to insights into its biological function...with great
potential for molecular modeling and designing new
sensors for monitoring other ions in a cell, according
to Randolph Addison, program director for signal transduction
and cellular regulation and Kamal Shukla, program
director in biomolecular structure and function. Both
NSF programs funded this work.
Since his discovery of aequorin 38 years ago, Shimomura's
life's work has been devoted to shedding light on
luminescence-a complex chemical reaction within an
organism's cells that results in the release of energy
in the form of light instead of heat. Shimomura determined
years ago that aequorin glows blue when tiny amounts
of calcium bind to it.
This discovery led to the use of aequorin as an important
biomedical tool for tracking the movement of calcium
within cells. Calcium plays a crucial role in the
regulation of a variety of biological processes including
fertilization, muscle contraction, and the transmission
of nerve impulses.
Much has been learned over the years about aequorin
and its regenerated form, apoaequorin. But, says Shimomura,
"We've been working blind for many years." Until now,
no one has been able to visualize the actual three-dimensional
crystal structure of this important protein, something
Osamu Shimomura has dreamed of doing since first discovering
aequorin.
Now that Shimomura and his colleagues know the exact
structure of aequorin, they'll be better able to study
how the protein functions in concert with other chemicals,
and, possibly, enhance its usefulness as a biological
marker.
"One of the most exciting outcomes of knowing the structure
of aequorin is that it offers the potential for us
to perhaps 'custom' design molecules that are able
to sense different molecules or ions," explains co-author
James Head of Boston University. "These would then
'wink' at us, with light emission, when a certain
molecule is encountered. It is possible that, based
on the current structure, we may be able to engineer
the protein to respond to different ions at different
ranges of concentrations, and conceivably combine
the aequorin structure with other protein domains
that bind entirely different molecules to produce
completely new sensors. This has the potential to
provide a family of biosensors for use in biological
systems, and, under the right conditions, possibly
also for use in industrial settings."
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