ATHENS, Ga. -- Fans of the comic-book character Green Lantern know he is a force against evil. Now, there is another green lantern -- and this one could become a force in understanding, among other things, how genes express their chemical instructions.
The new green lantern is a newly described three-dimensional structure of a fluorescent protein found in jellyfish, a structure that looks like a glowing green lantern. The discovery, by crystallographers at the University of Georgia, could help make it easier to use the protein as a biomarker.
"Seeing the crystal structure of this protein as a green lantern was quite unexpected," said Dr. B.C. Wang, Eminent Scholar and Professor in the department of biochemistry and molecular biology at UGA. "Now that we know the structure, it will be easier for researchers to modify the molecule to increase its efficiency as a biomarker."
The new study by Wang and colleagues at the University of Georgia, the Scripps Institute of Oceanography, the University of California at San Diego and the University of Oregon was presented at the 9th International Symposium on Bioluminescence and Chemiluminescence at Woods Hole, Mass., in October.
Wang's research builds on previous work from the University of Oregon and the University of Texas. Researchers at Oregon first described the structure of the monomer form of the protein. (A monomer is a single molecule that can be chemically bound as a unit of a polymer.) And scientists at Texas first described the molecule's dimer form. (A dimer is a molecule consisting of two identical simpler molecules.)
But the studies described at the conference in October were for a dimer-form crystal in which the molecules are packed in a more complex manner than the ones studied at Texas, thus setting the stage for understanding how to change the molecule into a powerful biomarker for use in chemical and medical research.
It has been known for centuries that the jellyfish Aequorea victoria has a greenish glow in the ocean. Researchers only found out in the past several decades, however, that the glow is caused by a chemical reaction that culminates in the physical interaction between a chemical called aequorin and a green fluorescent protein (GFP). The mixing of these compounds causes the jellyfish to give off a green glow -- an eerie sight, no doubt, to early sailors in the world's oceans.
While the series of chemical interactions necessary to create the glow are difficult to recreate in the laboratory, there is a much easier way, a mechanical method that does the same thing. By exposing GFP to ultraviolet or microscope light, the characteristic glow can be achieved. But it was only when Wang and his team began to use the powerful techniques of X-ray crystallograhy that they noticed something unusual about the structure of the crystal.
"We found that, quite amazingly, it was in the shape of a lantern," said Wang. "It has the dinstinctive structural feature of a barrel or protective shield on the outside and a light-generating element called a chromophore at the center."
The reason the GFP protein resembles a green lantern is not at all clear, but Wang believes that it shows how structure evolved with function in the protein. Since the chromophore requires no direct interaction with other molecules in order to absorb or emit light, there is no need for it to be exposed in the protein structure for easy access.
For the conference at Woods Hole, Wang actually constructed a "green lantern" using rolled paper and a small flashlight that showed how the chromophore glowed inside its protective cage or shield. The device looks somewhat like a traditional Chinese lantern.
"The location of the chromophore in the center of the shell makes a perfect structural sense in terms of its functional role," said Wang.
The significance of the new understanding of GFP is not yet clear, but Wang expects that knowing the structure of the "green lantern" will open the doors for further research into making GFP a powerful marker for gene expression and cell lineage and as a tag for fusion proteins.
(Editors/writers: Copies of the paper are available by fax. Call Phil Williams at the above address for more information.)