Studies on the structures and mechanisms of algal photoreceptors

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Light-dependent responses play major roles not only in the morphogenesis of higher plants, but also in the regulation of cellular responses by green and red algae. Several cryptochromes are now demonstrated to mediate blue-light and, in the case of aCRY from Chlamydomonas reinhardtii, even red-light responses in green algae. An important prerequisite for understanding their in vivo photobiology is first the identification of cognate antenna cofactors in algal cryptochromes. Secondly, analysis of their redox-state dependent structures will then allow to correlate their photochemistry and signalling function with structural alterations and delineate interaction sites with putative downstream regulators. Aureochromes are a novel class of blue-light-dependent transcription factors, which are found only in several algae and differ by their inverted domain organisation from other LOV-regulated signalling proteins. We will analyse their lit state structures by X-ray crystallography when complexed to cognate DNA and compare them with their dark state structures. Here, the final goal is to obtain the molecular basis for intra-molecular signal transfer and transcription activation by aureochromes.