This morning, the Nobel committee recognized the work of Osamu Shimomura, Martin Chalfie and Roger Tsien “for the discovery and development of the green fluorescent protein, GFP” by awarding them the Nobel Prize in Chemistry for 2008. A video of a great lecture on fluorescent proteins by Roger Tsien is available here.
Shimomura first discovered GFP during the study of the bioluminescent protein aequorin, the mechanism by which certain jellyfish glow. In the footnote to his seminal paper on aequorin purification, he noted the additional presence of “a protein giving solutions that look slightly greenish in sunlight through only yellowish under tungsten lights, and exhibiting a very bright, greenish ﬂuorescence in the ultraviolet of a Mineralite, has also been isolated from squeezates.”
Chalfie took the cDNA of GFP and first expressed it bacteria and worms. He demonstrated GFP could be used as a molecular tag. Surprisingly, the protein folded and functioned without the use of co-factors specific to the jellyfish.
Tsien developed GFP into the many useful variants we use today. He reported the S65T point mutation that greatly improved its fluorescent characteristics. His lab also evolved GFP into many other color variants, and demonstrated that these variants could be used as genetically-encoded intracellular sensors for calcium, enzyme action, and glutamate.
The odd man out in this triumvirate is Douglas Prasher. With a tiny lab and budget, Prasher discovered the primary sequence of GFP and cloned the cDNA of GFP. Unfortunately, around the time of his work’s publication, his grant ran out. Prasher sent out DNA samples to Chalfie, Tsien and others, shut down his lab and left science. Prasher’s contribution was the essential foundation for the explosion of developments in the field.
Some argue that Tsien would have already won the Nobel prize for calcium signaling if not for his contribution to GFP. As a graduate student, he invented the high affinity calcium chelator BAPTA. Using BAPTA as a foundation, he created a large family of fast, bright calcium dyes, including fura-2. Nearly every fluorescent dye for calcium was either his invention or a close variant of one of these. The importance of these tools for understanding intracellular communication cannot be overstated.