The color-transitions of bilin photoreceptors

具有开链四吡咯的光感受器(Bilins)形成了一大类光依赖的开关，就像研究得很好的光致变色剂一样。聚合型光致变色剂经历了光化学双键异构化和介观软到硬的转变，并伴随着从红色到远红色的颜色转变。2001年，Ohmori和Ikeuchi发现了蓝藻色素(CBCRs)，在一些研究中也被称为氰色蛋白或GAF-Only蛋白，这导致了Blin光感受器的光物理和光化学范式的改变。突然间，很明显，经典的光感受器，光致变色剂，只构成了碧林光化学中未知的光化学参数的巨大景观中的一个特例。这一事实提醒我们，尽管有大量的实验研究，但对光敏色素颜色变化的起源也没有足够的了解。在这里，我们的目标是对碧林光感受器的颜色物理和化学有一个共同的看法。为此，结合实验核磁共振波谱和理论QM/MM模拟，我们的目标是纠缠控制BLIN蛋白质颜色转变的因素。基于X-射线结构和核磁共振数据，我们将首先重建典型的Cph1光敏色素和CBCR AnPixJg2的Pr态的分子轨道结构。在接下来的工作中，我们将重建光产物Cph1PFR(远红吸收)和AnPixJg2PG(绿色吸收)的结构和轨道结构。通过比较PFR和PG，我们期望对色彩调谐有概念性的了解。

Photoreceptors with open-chain tetrapyrroles (bilins) form a large class of light-dependent switches as the well-studied phytochromes. The paradigmatic phytochromes undergo photochemical double-bond isomerisation and mesoscopic soft-to-hard transition accompanied by a color transition from red to far-red. The discovery of cyanobacteriochromes (CBCRs), in some studies also named as cyanochromes or GAF-only proteins, by Ohmori and Ikeuchi in 2001 led to a change of paradigm in photophysics and photochemistry of bilin photoreceptors. Suddenly it became evident that the classical photoreceptors, the phytochromes, constitute only a special case in remarkably huge landscape of unknown photochemical parameters of bilin photochemistry. That fact minded us that, although plenty of experimental studies, the origin of the color change in phytochromes is not sufficiently understood too. Here we aim for a common view on the color physics and chemistry of bilin photoreceptors. To this end, combining experimental NMR spectroscopy with theoretical QM/MM simulations, we aim to entangle the factors controlling the color transitions in bilin proteins. Based on the X-ray structures and NMR data, we will first reconstruct the molecular orbital architecture of Pr states of canonical Cph1 phytochrome and the CBCR AnPixJg2. In the following, we will reconstruct structure and orbital architecture of the photoproducts Cph1 Pfr (far-red absorbing) and AnPixJg2 Pg (green absorbing). By comparing Pfr and Pg, we expect to obtain conceptual understanding of the color tuning.