文章基本信息

标题：Structural elements regulating the photochromicity in a cyanobacteriochrome
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作者：Xiuling Xu ; Astrid Port ; Christian Wiebeler 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2020
卷号：117
期号：5
页码：2432-2440
DOI：10.1073/pnas.1910208117
出版社：The National Academy of Sciences of the United States of America
摘要：The three-dimensional (3D) crystal structures of the GAF3 domain of cyanobacteriochrome Slr1393 ( Synechocystis PCC6803) carrying a phycocyanobilin chromophore could be solved in both 15- Z dark-adapted state, Pr, λ_max = 649 nm, and 15- E photoproduct, Pg, λ_max = 536 nm (resolution, 1.6 and 1.86 Å, respectively). The structural data allowed identifying the large spectral shift of the Pr-to-Pg conversion as resulting from an out-of-plane rotation of the chromophore’s peripheral rings and an outward movement of a short helix formed from a formerly unstructured loop. In addition, a third structure (2.1-Å resolution) starting from the photoproduct crystals allowed identification of elements that regulate the absorption maxima. In this peculiar form, generated during X-ray exposition, protein and chromophore conformation still resemble the photoproduct state, except for the D-ring already in 15- Z configuration and tilted out of plane akin the dark state. Due to its formation from the photoproduct, it might be considered an early conformational change initiating the parental state-recovering photocycle. The high quality and the distinct features of the three forms allowed for applying quantum-chemical calculations in the framework of multiscale modeling to rationalize the absorption maxima changes. A systematic analysis of the PCB chromophore in the presence and absence of the protein environment showed that the direct electrostatic effect is negligible on the spectral tuning. However, the protein forces the outer pyrrole rings of the chromophore to deviate from coplanarity, which is identified as the dominating factor for the color regulation.
关键词：crystal structure ; photochromicity ; phytochrome ; theoretical chemistry