Many light responses of bacteria, plants and animals are governed by the blue region of the sun's spectrum. Examples are the growth of plants towards the light and the setting of the daily rhythm in animals. Blue light photoreceptors are proteins that sense the light conditions and transfer this information to the organism. We are investigating the molecular mechanisms of this signal transfer inside the protein directly after light absorption using time-resolved electronic and vibrational spectroscopy. For an overview see Nachrichten aus der Chemie 2011 (in German).

Phototropin

Plants use the blue light receptor phototropin to optimize photosynthesis and to prevent harmful exposure to strong irradiation by photomovement responses. Phototropin contains two so-called LOV domains that incorporate a flavin mononucleotide, a derivative of vitamin B2, as a light-absorbing molecule. Blue light causes the formation of a covalent linkage in the LOV domains between the flavin and the protein. After many seconds, this linkage breaks and thereby the sensor is regenerated. The steps of the photocycle and its kinetics have been intensively studied by us (see Biophys. J. 2003). However, the mechanism of signal transfer from the inside of the LOV domain to the outside is still unclear. For our current model see Biochemistry 2010.

Cryptochrome

Cryptochromes are found in all kingdoms of life. They play a key role in the daily rhythmicity of plants and animals including humans. Besides a light-independent function as part of the internal clock, cryptochromes regulate a variety of responses to blue light such as the setting of the clock in the fly Drosophila and the growth of the small weed Arabidopsis. All cryptochromes contain a flavin adenine dinucleotide (FAD) as a chromophore. Very little is known about the processes inside the protein after light absorption. Our goal is to identify the light-induced changes in cryptochrome by using time-resolved spectroscopy. For first results see JACS 2009, J. Phys. Chem. B 2010, JACS 2012.

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