Phytochrome proteins guide the red/far-red photoresponse of plants, fungi, and bacteria. Crystal structures suggest that the mechanism of signal transduction from the chromophore to the output domains involves refolding of the so-called PHY tongue. It is currently not clear how the two other notable structural features of the phytochrome superfamily, the so-called helical spine and a knot in the peptide chain, are involved in photoconversion. Here, we present solution NMR data of the complete photosensory core module from Deinococcus radiodurans. Photoswitching between the resting and the active states induces changes in amide chemical shifts, residual dipolar couplings, and relaxation dynamics. All observables indicate a photoinduced structural change in the knot region and lower part of the helical spine. This implies that a conformational signal is transduced from the chromophore to the helical spine through the PAS and GAF domains. The discovered pathway underpins functional studies of plant phytochromes and may explain photosensing by phytochromes under biological conditions.

光敏色素蛋白引导植物、真菌和细菌的红色/远红色光响应。晶体结构表明，从发色团到输出域的信号转导机制涉及所谓的 PHY 舌的重新折叠。目前尚不清楚光敏色素超家族的另外两个显着结构特征，即所谓的螺旋棘和肽链中的结，如何参与光转换。在这里，我们展示了耐辐射奇异球菌的完整光感核心模块的溶液核磁共振数据. 静止状态和活性状态之间的光切换会引起酰胺化学位移、残余偶极耦合和弛豫动力学的变化。所有观察结果都表明在结区和螺旋脊柱下部发生了光诱导的结构变化。这意味着构象信号通过 PAS 和 GAF 域从生色团转导到螺旋脊柱。发现的途径支持植物光敏色素的功能研究，并可能解释生物条件下光敏色素的光敏作用。