Zebrafish
Learning from Fish How other species can teach us about ourselves
Disease
Genetics
 | What is so special about GFP?Nature is full of colours, blood red, banana yellow, orange orange, blueberry blue, what is so special about GFP?. Well, first of all it is a fluorescent colour, which means that if you shine light on it with one wavelength (blue) the molecule of GFP can absorb that light and respond by sending out light with a slightly longer wavelength (green). This in itself is nothing special because there a numerous chemicals which have that property, but it means it is can be detected in very small quantities when you have the right equipment down to single molecules! You might say it is a super-bright colour. |
So if there are many chemicals in animals and plants that are fluorescent what makes GFP stand out?Most colours in nature are complex chemical molecules that are made in a lot of small steps, and each step requires a different protein. To give an example the red colour of roses needs at least five different proteins to be produced from a common biochemical molecule. In order to make a fish “rose-red” one would have to make sure that the original biochemical molecule is present in sufficient quantities and all the proteins are present and also will work in a “fish environment” – this is really difficult. GFP and related proteins are unique because they are enzymes that will act on themselves: they will modify their own amino acids to produce a fluorescent colour. All a scientist needs to do to get that colour in to a fish is to put the coding sequence of the gene into a fish, the protein that is produced will take care of everything else. Where does GFP come from?Green fluorescent protein was originally identified and isolated from a jellyfish Aequorea Victoria in 1962 by Osamu Shimomura. In the jellyfish it constitutes a component of a bioluminescent organ that lights up in the dark. The sequence of the gene was determined in 1992. When people realized its fantastic properties new “expeditions” to find further similar proteins were launched (literally! ….diving for fluorescent corals).
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| Genetic tinkering of the original and newly found proteins was used to improve its brightness, stability and colour. As a result of these efforts we now have a palette that would make even Vincent van Gogh jealous. More exotic variants of GFP have been made, a good example is called “Timer” as the name implies this protein can measure time. When it is just made it has a green colour but when it ages is slowly turns red. If such a protein is made in a cell for one hour and then production stops, one would see the cell colour like a traffic light: green first, then yellow (red+green), then red and then fade again as the protein is degraded over time. What does GFP look like? The three dimensional structure of proteins can be determined using a very sophisticated technique that reconstructs this structure from the way a crystal of the protein in questions diffracts X-rays. The result was a very compact and elegant barrel shaped molecule where the fluorescent part of the protein is buried in the inside of the barrel.
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| Copyright University of Sheffield 2011 |
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