The Aequorea victoria jellyfish is found in the Pacific Ocean, off the West coast of North America. It can produce bioluminescence via the protein aequorin, which produces flashes of blue light when calcium binds to it. The blue light is then absorbed by green fluorescent protein (GFP), which then emits green light. The biological purpose of the bioluminescence is not clear.
Aequorin and GFP were first identified by Osamu Shimomura in 1962 and since then both have been developed as tools for research. Aequorin is used as a calcium reporter in mammalian cells, plants and fungi. One of the advantages of aequorin over fluorescence-based calcium reporters is that the luminescence is produced without any need for a light source. Another advantage is that whilst most protein reporters can only be used in a recombinant system where the gene encoding that reporter is transformed into and expressed in the cells, the aequorin protein can also be injected directly into cells. Aequorin is made up of an apoprotein and a prosthetic group, the small molecule coelenterazine. Coelenterazine is consumed in the process of producing the luminescence. It is irreversibly excited by calcium binding to apo-aequorin to generate the blue light, so in an experimental set up the coelenterazine supply may need to be replenished.
GFP is often used as a reporter for visualizing the localization of proteins within a cell. The DNA sequence encoding GFP can be connected to the DNA sequence of a gene of interest. This fusion gene can then be transformed into an organism. When the fusion gene is expressed the resulting fusion protein can be detected with fluorescence microscopes by using blue light to excite GFP and measuring the amount of green fluorescence. Many derivatives of GFP have been developed that emit different wavelengths of light, for example cyan fluorescent protein (CFP) and yellow fluorescent protein (YFP). There are now many tools that use this family of proteins, including a system for detecting protein-protein interactions by Bimolecular Fluorescence Complementation (BiFC) , and the calcium reporter Cameleon.
The development of GFP has had such a large impact on research that in 2008 Osamu Shimomura, Martin Chalfie and Roger Y. Tsien were awarded the Nobel Prize for Chemistry “for the discovery and development of the green fluorescent protein, GFP”. My PhD research would be much more difficult without GFP and its derivatives so I for one am very grateful.
For more information the research uses of GFP and its derivatives visit: http://www.conncoll.edu/ccacad/zimmer/GFP-ww/
1999-present. Bioluminescence of Aequorea, a hydromedusa. Electronic
internet document available at
http://faculty.washington.edu/cemills/Aequorea.html. Published by the author,
web page established June 1999, last updated 2009.