Molecular Understanding of the Photophysics and Photochemistry of the Cyanobacteriochrome Slr1393g3

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The proposed research project will result in an understanding of the photophysical, e.g. absorption of visible light, and photochemical, e.g. isomerization mechanism of the chromophore, properties of the photoreceptor protein Slr1393g3 on the molecular level. For this purpose, two different forms of the protein (reactant and product) will be investigated: one form absorbs red light and the other one green. Both forms can be interconverted into each other by light illumination. Therefore, they are promising candidates for the use as photoswitches in biotechnological applications.Experimentally determined crystal structures will be the starting point of the computational investigations. The research project benefits of my previous experiences regarding phohtophysics and photochemistry of conjugated systems and photochromic molecules, which was the topic of my PhD. It is divided in to main projects. The first project will establish a universal protocol for the determination of the spectroscopic, i.e. photophysical, properties of both forms employing the QM/MM method. the second one is concerned with the photochemical properties: Starting with the determination of an adequate quantum mechanical method for the calculation of the light-induced dynamics for a small model system, this method will be used in an QM/MM model to simulate the dynamics of the chromophore-protein complex. In addition, the reactivity in the excited state will be predicted with minimum energy paths. The envisaged approach, which combines experiment and theory, will yield a fundamental understanding of the different photophysical and photochemical properties of both forms of the protein. The insights obtained this way will be used to specifically tune the static and dynamical properties. At every stage of the research project, our calculated results will be compared with experiment to verify our modeling or to improve our models if necessary. Finally, the obtained detailed understanding on a molecular level will be the basis for the knowledge-based design of photoreceptor proteins in the future.