Bielefeld University Department of Chemistry Biophysical Chemistry and Photochemistry deutsch


Light Sensors and Optogenetics

Many light responses of animals, plants, fungi and bacteria are governed by the blue region of the sun's spectrum. Examples are the growth of plants towards the light (phototropism) and the setting of the daily rhythm in animals (circadian rhythm).

Blue light photoreceptors are proteins that allow the organism to sense the light conditions in the environment. We are investigating the mechanisms of the signal transfer inside the protein from nanoseconds to minutes using time-resolved vibrational and electronic spectroscopy.
For an overview see Nachr. Chem. 2011 (in German).

All blue light receptors are used as tools in optogenetics to render biological processes artificially light-sensitive. For the development and application of this tools, an understanding of the mechanisms is essential.

Cryptochromes

Cryptochromes are used by all organisms, but strongly differ in function and mechanism. They play a key role in the daily rhythmicity of plants and animals including humans. Cryptochromes regulate a variety of responses to blue light such as plant development (photomorphogenesis) and the setting of the clock in insects. Even a function as sensor of the magnetic field has been demonstrated.

All cryptochromes contain a derivative of vitamin B2 (flavin adenine dinucleotide) as a chromophore. Our goal is to identify the light-induced processes in cryptochrome by using time-resolved spectroscopy.
(see JACS 2009, J. Phys. Chem. B 2010, JACS 2012, JACS 2015)

Surprisingly, an animal-like cryptochrome (aCRY) has been identified in green algae, which does not only detect blue but also red light. Therefore, we have identified and characterized the first flavin-containing protein, which is activated by red light (see Plant Cell 2012, J. Biol. Chem. 2017).

Phototropin

Plants use the blue light receptor phototropin to optimize photosynthesis and to prevent harmful exposure to strong irradiation (see Nature 2016).

Phototropin contains two so-called LOV domains that bind a flavin mononucleotide as a light-absorbing molecule. Blue light causes the formation of a covalent linkage 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). Currently, we are dealing with the question of how the signal is transfered inside the protein from sensor to effector (a kinase domain). For our model see Biochemistry 2010.

Aureochrome

Some algae use an aureochrome instead of a phototropin as blue light sensor. Aureochromes contain a sensory LOV domain as well, but the effector is a DNA-binding domain (bZIP domain). Consequently, aureochromes most likely act as light-controlled transcription factors, which is of high interest for biotechnology.

The arrangement of sensor and effector is inverted in comparison to phototropin. We investigate, how a signal can be transfered to the bZIP domain in this inverted arrangement and how thereby the DNA binding is modified. (see Biochemistry 2013, Biochemistry 2015, Nucleic Acids Research 2017).


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