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Projekt
Light responses of animal-like cryptochromes and aureochromes from microalgae
Antragsteller
Professor Dr. Tilman Kottke
Fachliche Zuordnung
Pflanzenphysiologie
Förderung
Förderung von 2009 bis 2017
Projektkennung
Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 112805507
Cryptochromes and aureochromes are plant photosensors incorporating a flavin as a chromophore. The mechanism and the role of these receptors in microalgae remain largely unclear. Cryptochromes regulate blue-light-dependent processes such as photomorphogenesis and circadian rhythm in higher plants. In the green alga Chlamydomonas reinhardtii, however, an additional animal-like cryptochrome (aCRY) is found. aCRY is currently the only sensory flavoprotein, which is activated not only by blue but also by red light. The structural basis of this unique red-light sensitivity of aCRY needs to be elucidated. We have demonstrated that heterologously expressed aCRY forms a neutral radical of flavin with an absorption spectrum similar to the spectral response in vivo. The neutral radical state was therefore postulated as dark state. The influence of reductants and point mutations on formation and stabilisation of this dark state will be investigated. The course of the photoreaction will be followed by time-resolved spectroscopy. aCRY differs from homologous proteins with a function as core clock component or DNA repair enzyme in a specific C-terminal extension. Infrared difference spectroscopy will be applied to search for lightdependent structural changes in this extension. Further promising candidates for sensory cryptochromes from microalgae will be characterized by spectroscopy. Aureochromes have only been identified in algae up to now including the diatom Phaeodactylum tricornutum. Aureochrome differs from all other proteins containing LOV (light-, oxygen-, or voltage-sensitive) domains such as phototropin in a reverse arrangement of effector and sensor domains. We have shown that despite the reverse arrangement, the C-terminal LOV-J(alpha) helix unfolds in aureochrome similar to phototropin. We will investigate the progress of signal transfer by the J(alpha) helix or other segments in the full-length AUREO1a using infrared double difference spectroscopy. The DNA binding ability of the putative transcription factor will be studied. Other aureochromes from P. tricornutum will be heterologously expressed and their photochemical properties will be analyzed with respect to their role in vivo. The investigation of the novel pathways of signal transfer in these aureochromes and cryptochromes will significantly broaden our current understanding of photosensors.
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