Invaluable as markers for monitoring photosynthesis and other energy-related processes in living cells, green fluorescent proteins (GFPs), discovered in a species of jellyfish, are vital in extremely high-resolution imaging studies. Scientists found that when water is added to the GFP's chromophore, the part of the molecule that gives the protein its color, the fluorescence is more stable. Water apparently shuts a channel that lets electrons escape, thus ending processes that reduce fluorescent light emission. The scientists' findings give a more accurate view of the physics of this extremely useful protein.
Understanding how to control the light emitted by GFPs could help scientists make this common scientific imaging label work more efficiently and, perhaps, glow more brightly when used to track reactions inside cells, essentially turning up the volume of this marker.
Green fluorescent protein (GFP) was first collected from the jellyfish Aequorea victoria off the western coast of North America and has revolutionized cellular biology since its discovery. This protein contains a small chain of three sequential amino acids that interact to give GFP its characteristic glow. GFP has been utilized in numerous studies as a marker protein that can track chemical reactions within living cells, along with various other uses.
Scientists at Pacific Northwest National Laboratory and colleagues at Louisiana State University essentially disassembled a model of the GFP piece by piece, examining each piece, and then put it back together to understand how it works. Using negative ion photoelectron spectroscopy and theoretical calculations, they created a probe to identify the exact structures involved in the GFP chromophore, showing that when the chromophore encounters water molecules, the first few molecules progressively stabilize the excited state of the chromophore.
That is, when water is added, the excited state that generates fluorescence is more stable. Water closes the channel to electron emissions, effectively shutting off competitive electron processes that quench fluorescence. The scientists' findings give a more accurate view of the physics of this extremely useful protein and could lead to even more ways to exploit this valuable monitor of biological processes.
This research was supported by DOE, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division.
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