Department of Physics, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany.
Molecules. 2022 Dec 1;27(23):8395. doi: 10.3390/molecules27238395.
Phytochromes are biological red/far-red light sensors found in many organisms. The connection between photoconversion and the cellular output signal involves light-mediated global structural changes in the interaction between the photosensory module (PAS-GAF-PHY, PGP) and the C-terminal transmitter (output) module. We recently showed a direct correlation of chromophore deprotonation with pH-dependent conformational changes in the various domains of the prototypical phytochrome Cph1 PGP. These results suggested that the transient phycocyanobilin (PCB) chromophore deprotonation is closely associated with a higher protein mobility both in proximal and distal protein sites, implying a causal relationship that might be important for the global large-scale protein rearrangements. Here, we investigate the prototypical biliverdin (BV)-binding phytochrome Agp1. The structural changes at various positions in Agp1 PGP were investigated as a function of pH using picosecond time-resolved fluorescence anisotropy and site-directed fluorescence labeling of cysteine variants of Agp1 PGP. We show that the direct correlation of chromophore deprotonation with pH-dependent conformational changes does not occur in Agp1. Together with the absence of long-range effects between the PHY domain and chromophore p, in contrast to the findings in Cph1, our results imply phytochrome species-specific correlations between transient chromophore deprotonation and intramolecular signal transduction.
光敏色素是许多生物中存在的生物红光/远红光光传感器。光转化与细胞输出信号之间的联系涉及到光介导的相互作用中的全局结构变化，该相互作用发生在光敏模块（PAS-GAF-PHY，PGP）和 C 端传输器（输出）模块之间。我们最近表明，发色团去质子化与原典型光敏色素 Cph1 PGP 的各个结构域中 pH 依赖性构象变化之间存在直接相关性。这些结果表明，瞬态藻蓝胆素（PCB）发色团去质子化与近端和远端蛋白质位点的蛋白质流动性增加密切相关，暗示这种瞬态关系可能对全局大规模蛋白质重排很重要。在这里，我们研究了典型的胆绿素（BV）结合型光敏色素 Agp1。使用皮秒时间分辨荧光各向异性和 Agp1 PGP 的半胱氨酸变体的定点荧光标记，研究了 Agp1 PGP 中各个位置的结构变化随 pH 的变化。我们表明，发色团去质子化与 pH 依赖性构象变化之间的直接相关性在 Agp1 中不存在。与 Cph1 的发现相反，我们的结果表明 PHY 结构域和发色团 p 之间不存在长程效应，这意味着在不同的植物光敏色素之间存在瞬态发色团去质子化与分子内信号转导之间的特定相关性。
