Shining protein

THREE scientists, one Japanese and two American, share this year’s Nobel Prize in Chemistry “for the discovery and development of the green fluorescent protein, GFP”. They are Osamu Shimomura, 80, of the Marine Biological Laboratory, Woods Hole in Massachusetts, and Boston University Medical School; Martin Chalfie, 61, of Columbia University, New York; and Roger Y. Tsien, 56, of the University of California, San Diego. Luminescence and fluorescence refer to light emission from cold bodies. The former results from chemical reactions or subatomic motions or stress on a crystal. In particular, it is referred to as bioluminescence when the luminescence occurs in living organisms, say a firefly, owing to chemical reactions within some part of the organism. Another bioluminescent organism is the jellyfish Aequorea victoria whose outer edge glows green when the jellyfish is agitated. Fluorescence is luminescence caused by external light stimuli as an optical phenomenon in which molecular absorption of a photon triggers the emission of another photon, usually of a longer wavelength. In 1955, Osamu Shimomura, after having been devastated by the War and the atomic bombing of Nagasaki where he lived, was employed as an assistant by a professor at Nagoya University. He was given the task of finding out what made the remains of a crushed mollusc, Cypridina, glow when it was moistened with water. This was a problem considered to be difficult even for professional researchers and, apparently, the professor not wishing to spoil the career of a research student over such a problem, put Shimomura on this task. However, in 1956, to the professor’s surprise, Shimomura isolated the glowing material. It was a protein that glowed 37,000 times more brightly than the crushed mollusc. This earned him a valuable gift of a Ph.D. from his professor even though he was not enrolled as a doctoral student. Armed with his results and the doctorate, he joined Princeton University under Frank Johnson, with whom he set about studying another bioluminescent organism, the jellyfish.During the whole of the summer of 1961, Shimomura and Johnson gathered jellyfish at Friday Harbour, Washington. They chopped off the edges of the jellyfish and pressed them through a filter to get what they called a squeezate. Serendipitously, on one occasion, when Shimomura poured some of the squeezate into the sink, he saw a bright blue flash, not green as in the jellyfish. He reckoned that the sea water in the sink, which contained calcium ions, caused the squeezate to luminesce. Johnson and Shimomura collected squeezate from about 10,000 jellyfish and took it to Princeton. It took them a few months to purify just a few milligrams of the blue luminescent material from the liquid. They named this protein aequorin. “There were many difficulties and troubles. But… somehow I found how to extract the protein,” Shimomura says in the post-award interview with the Nobel Foundation’s website. “And after finding that, what we needed to do to study that protein was to get large amounts of that protein. So, we collected huge numbers of jellyfish by going to Friday Harbour every summer, with a schedule of 50,000 per summer, in one or two months,” he adds. They did this apparently for 19 summers and accumulated a total of 850,000 jellyfish. In 1962, when Shimomura and Johnson published their isolation of aequorin, they mentioned that they had also isolated another protein, which was slightly greenish in sunlight, yellowish in the light from an incandescent bulb and green in ultraviolet light. This was a fluorescent protein (as against the luminescent aequorin), which they called the “green protein”, but later it came to be called green fluorescent protein (GFP).