Facts About Green Fluorescent Protein

Green fluorescent protein in the bacteria Escherichia.
Green fluorescent protein in the bacteria Escherichia. Fernan Federici / Getty Images

Green fluorescent protein (GFP) is a protein that occurs naturally in the jellyfish Aequorea victoria. The purified protein appears yellow under ordinary lighting, but glows bright green under sunlight or ultraviolet light. The protein absorbs energetic blue and ultraviolet light and emits it as a lower energy green light via fluorescence. The protein is used in molecular and cell biology as a marker. When it is introduced into the genetic code of cells and organisms, it is heritable. This has made the protein not only useful to science, but of interest making transgenic organisms, such as fluorescent pet fish.

The Discovery of Green Fluorescent Protein

The crystal jelly, Aequorea victoria, is the original source of green fluorescent protein.
The crystal jelly, Aequorea victoria, is the original source of green fluorescent protein. Mint Images - Frans Lanting / Getty Images

The crystal jellyfish, Aequorea victoria, is both bioluminescent (glows in the dark) and fluorescent (glow in response to ultraviolet light). Small photoorgans located on the jellyfish umbrella contain the luminescent protein aequorin that catalyzes a reaction with luciferin to release light. When aequorin interacts with Ca2+ ions, a blue glow is produced. The blue light supplies the energy to make GFP glow green.

Osamu Shimomura conducted research into the bioluminescence of A. victoria in the 1960s. He was the first person to isolate GFP and determine the part of the protein responsible for fluorescence. Shimomura cut the glowing rings off of a million jellyfish and squeezed them through gauze to obtain the material for his study. While his discoveries led to a better understanding of bioluminescence and fluorescence, this wild-type green fluorescent protein (wGFP) was too difficult to obtain to have much practical application. In 1994, GFP was cloned, making it available for use in laboratories around the world. Researchers found ways to improve upon the original protein to make it glow in other colors, glow more brightly, and interact in specific ways with biological materials. The immense impact of the protein on science led to the 2008 Nobel Prize in Chemistry, awarded to Osamu Shimomura, Marty Chalfie, and Roger Tsien for "the discovery and development of the green fluorescent protein, GFP."

Why GFP Is Important

Human cells colored with GFP.
Human cells colored with GFP. dra_schwartz / Getty Images

No one actually knows the function of bioluminescence or fluorescence in the crystal jelly. Roger Tsien, the American biochemist who shared the 2008 Nobel Prize in Chemistry, speculated the jellyfish might be able to change the color of its bioluminescence from the pressure change of changing its depth. However, the jellyfish population in Friday Harbor, Washington, suffered a collapse, making it difficult to study the animal in its natural habitat.

While the importance of fluorescence to the jellyfish is unclear, the effect the protein has had on scientific research is staggering. Small fluorescent molecules tend to be toxic to living cells and negatively affected by water, limiting their use. GFP, on the other hand, can be used to see and track proteins in living cells. This is done by joining the gene for GFP to the gene of a protein. When the protein is made in a cell, the fluorescent marker is attached to it. Shining a light at the cell makes the protein glow. Fluorescence microscopy is used to observe, photograph, and film living cells or intracellular processes without interfering with them. The technique works to track a virus or bacteria as it infects a cell or to label and track cancer cells. In a nutshell, the cloning and refining of GFP has made it possible for scientists to examine the microscopic living world.

Improvements in GFP have made it useful as a biosensor. The modified proteins as act molecular machines that react to changes in pH or ion concentration or signal when proteins bind to each other. The protein can signal off/on by whether or not it fluoresces or can emit certain colors depending on the conditions.

Not Just for Science

GloFish genetically modified fluorescent fish get their glowing color from GFP.
GloFish genetically modified fluorescent fish get their glowing color from GFP. www.glofish.com

Scientific experimentation isn't the only use for green fluorescent protein. The artist Julian Voss-Andreae creates protein sculptures based on the barrel-shaped structure of GFP. Laboratories have incorporated GFP into the genome of a variety of animals, some for use as pets. Yorktown Technologies became the first company to market fluorescent zebrafish called GloFish. The vividly colored fish were originally developed to track water pollution. Other fluorescent animals include mice, pigs, dogs, and cats. Fluorescent plants and fungi are also available.

Recommended Reading

  • Chalfie M, Tu Y, Euskirchen G, Ward WW, Prasher DC (Feb 1994). "Green fluorescent protein as a marker for gene expression". Science. 263 (5148): 802–5.
  • Shimomura O, Johnson FH, Saiga Y (Jun 1962). "Extraction, purification and properties of aequorin, a bioluminescent protein from the luminous hydromedusan, Aequorea". Journal of Cellular and Comparative Physiology59 (3): 223–39.
  • Tsien RY (1998). "The green fluorescent protein" (PDF). Annual Review of Biochemistry. 67: 509–44.