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A Biomolecule As A Light Switch

September 30, 2005
Max Planck Society
Researchers at the Max Planck Institute for Biophysical Chemistry in Goettingen, Germany have uncovered the molecular mechanism of switchable fluorescent proteins, able to switch themselves reversibly back-and-forth between an "on" and "off" state. The discovery could be of importance for, among other purposes, optical data storage in protein crystals.

Snakelocks Anemone (Anemonia sulcata).
Credit: Image : Richard Lockett

Switchable fluorescent proteins - able to switch themselvesreversibly back-and-forth between an "on" and "off" state - have beenknown for only a few years. However, they already hold promise for alarge number of novel applications, from cellular biology to datastorage. Cell biologists, X-Ray crystallographers, photobiophysicists,and computer-biophysicists from Goettingen have worked together on aproject uncovering the molecular mechanism by which a fluorescentprotein becomes switched (PNAS, September 13, 2005). This knowledgecould be of importance for, among other purposes, optical data storagein protein crystals.

The fluorescent protein identified asasFP595 is found on the ends of the tentacles of the snakelocks anemoneAnemonia sulcata, a type of coral which lives in the Mediterranean Seaand North Atlantic, in the areas near the surface of the water, whichare flushed with light (see Fig. 1). In the tentacle ends, this proteinprobably protects the anemone’s tissue from solar rays that are toostrong. asFP595 absorbs green light and eventually emits redfluorescent light. When another light is applied to it, the protein canbe switched back-and-forth between a fluorescent and non-fluorescentstate. It is a so called "molecular light switch."

Theresearchers from Goettingen have uncovered the mechanism behind thismolecular switch. They fabricated the protein in bacteria, and then,from the purified protein, cultivated crystals that still had theswitching characteristics of the free protein. X-ray structuralanalysis and computer simulations showed that the chromophore - thepart of the protein that absorbs the light - changes structure when itis lit up using a cis-trans isomerisation. The chromophore does what iscalled a "hula twist", changing its position merely 3x10-10 m - a third of a billionth of a meter. This tiny change is enough to turn the fluorescent protein into a non-fluorescent one.

Basedon this knowledge, the researchers want to hone the protein with thegoal of using it in various applications. They range fromhighest-resolution microscopy all the way to optical data storage inprotein crystals.

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