Switchable fluorescent proteins, able to move reversibly between two optical states, have been known from some years. But now, German researchers have discovered the mechanism behind this optical switch in a protein found on the tentacles of a sea anemone. In "A biomolecule as a light switch," they explain they even were able to produce protein crystals which exhibit the same switching characteristics. These cultivated protein crystals might one day lead to new optical data storage devices. As this process is just appearing in the lab, it's too early to tell if such devices will be economically competitive. But even if the idea to use proteins from sea anemonia to build storage devices doesn't translate into commercial products anytime soon, it is at least a very poetic one...
Here are the explanations of these researchers at the Max Planck Institute for Biophysical Chemistry.
The fluorescent protein identified as asFP595 is found on the ends of the tentacles of the snakelocks anemone Anemonia sulcata, a type of coral which lives in the Mediterranean Sea and North Atlantic, in the areas near the surface of the water, which are flushed with light.
In the tentacle ends, this protein probably protects the anemone's tissue from solar rays that are too strong. asFP595 absorbs green light and eventually emits red fluorescent light. When another light is applied to it, the protein can be switched back-and-forth between a fluorescent and non-fluorescent state. It is a so called "molecular light switch."
Below is an illustration showing the overall structure of the fluorescent protein known as asFP595. "A schematic ribbon representation of "the quaternary tetrameric structure of asFP595 shows the four molecules in"different colors and the chromophores highlighted in red. (Credit: Max Planck Society).
So the researchers say they found the mechanism behind this molecular switch, but the Max Planck Society news release doesn't really describe the process. Instead, it is telling us what the researchers did after discovering this mechanism.
They fabricated the protein in bacteria, and then, from the purified protein, cultivated crystals that still had the switching characteristics of the free protein. X-ray structural analysis and computer simulations showed that the chromophore -- the part of the protein that absorbs the light -- changes structure when it is lit up using a cis-trans isomerisation. The chromophore does what is called a "hula twist", changing its position merely 3x10-10 m -- a third of a billionth of a meter.
The latest research work about this molecular light switch has been published by the Proceedings of the National Academy of Sciences under the name "Structure and mechanism of the reversible photoswitch of a fluorescent protein" (September 13, 2005, Vol. 102, No. 37, Pages 13070-13074).
Here are two links to the abstract and to the full paper (PDF format, 5 pages, 516 KB). The above image comes from this paper.
As a conclusion, it's interesting to note that these switchable fluorescent proteins could lead to several classes of applications, "including three dimensional data optical memories, protein tracking and live cell imaging at the nanoscale."
Sources: Max Planck Society press release, September 29, 2005; and various web sites
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