Green Fluorescent Protein
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Anemone sulcata Snake-locks sea anemone Courtesy of
Lukyanov et. al. |
Trachyphyllia geoffroyiStony ‘green open brain’ coral Courtesy of Oz |
A Rainbow of Colours
Since the discovery of GFP there have been 52 homologous proteins deposited into sequence databases that have been isolated from other Cnidarians, including various corals and anemones. One of the most striking finds is that only a few come from bioluminescent organisms; the majority were isolated from fluorescent and coloured animals that had no bioluminescence. This means that in most cases GFP-like proteins are not part of a bioluminescent system, but are simply part of animal colouration. Furthermore, ranges of different colours were found. These proteins are often classified according to their colour: green (GFP), yellow (YFP), red or orange-red (RFP), and non-fluorescent purple-blue chromoproteins (CP). These different proteins are responsible for much of the legendary variety of reef colours, with their abundance of coral fluorescence.
Interestingly, both fluorescent and non-fluorescent proteins can be found in the same organism. In the snake-locks sea anemone, Anemonia sulcata (above), the tentacles exhibit three different hues in daylight: green on the upper side, orange on the underside, and a red-purple on the tips. After UV-irradiation, the tentacles exhibit bright green and orange fluorescence, while the red-purple tips are non-fluorescent.
The diversity of GFP-like proteins has had an impact on biotechnology. These proteins expand the colour range available, permitting multicolour labelling. Some of these proteins have interesting features as well. The stony 'green open brain' coral, Trachyphyllia geoffroyi (above), has a fluorescent protein named Kaede, after the Japanese word for maple leaf. Kaede emits green fluorescence after synthesis that changes to a stable red fluorescence after UV irradiation, making this protein useful as an optical cell marker.
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