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Blue light sensing photoreceptor proteins in plants and bacteria are found to control physiological responses such as photosynthesis gene expression, photophobia and phototaxis(Gauden et al., PNAS, 2006, 103, 10895). In contrast to other types of photoreceptors such as rhodospins or phytochromes which undergo large conformational changes, only a 10nm shift in the absorption spectra of the dark and signaling states has been observed(S. Masuda and C. Bauer, Cell, 2002, 110, 613). In spite of the huge amount of experimental data available (crystal structures, NMR, FTIR, spectroscopy), the structure of the signaling state (lifetime > 2 minutes!) together its formation mechanism is still not fully known and a subject of controversy. We study one member of this protein family, BlrB (structure taken from Jung et al., PNAS, 2005,102,12350). By treating the chromphore and its close vicinity at the QM-level (DFT and MP2 for ground state, TD-DFT and CC2 for excited state) and the rest of the protein at MM level (QM/MM scheme), we aim to find an explanation for the behavior of this photoreceptor in it biologically active form. |
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