Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 1495 Berlin, Germany.
Fritz Haber Center for Molecular Dynamics Research, Institute of Chemistry, The Hebrew University of Jerusalem, Givat Ram, Jerusalem 9190401, Israel.
Molecules. 2020 Feb 14;25(4):848. doi: 10.3390/molecules25040848.
Channelrhodopsins (ChR) are light-gated ion-channels heavily used in optogenetics. Upon light excitation an ultrafast all- to 13- isomerization of the retinal chromophore takes place. It is still uncertain by what means this reaction leads to further protein changes and channel conductivity. Channelrhodopsin-1 in exhibits a 100 fs photoisomerization and a protonated counterion complex. By polarization resolved ultrafast spectroscopy in the mid-IR we show that the initial reaction of the retinal is accompanied by changes in the protein backbone and ultrafast protonation changes at the counterion complex comprising Asp299 and Glu169. In combination with homology modelling and quantum mechanics/molecular mechanics (QM/MM) geometry optimization we assign the protonation dynamics to ultrafast deprotonation of Glu169, and transient protonation of the Glu169 backbone, followed by a proton transfer from the backbone to the carboxylate group of Asp299 on a timescale of tens of picoseconds. The second proton transfer is not related to retinal dynamics and reflects pure protein changes in the first photoproduct. We assume these protein dynamics to be the first steps in a cascade of protein-wide changes resulting in channel conductivity.
通道蛋白（ChR）是光遗传学中广泛使用的光门控离子通道。在光激发下，视黄醛发色团会发生超快的全-13-顺式异构化。目前尚不清楚这一反应如何导致进一步的蛋白质变化和通道导电性。[X]中的通道蛋白-1具有 100fs 的光致异构化和质子化的抗衡离子复合物。通过中红外偏振分辨超快光谱，我们表明视黄醛的初始反应伴随着蛋白质骨架的变化和抗衡离子复合物（包含 Asp299 和 Glu169）中的超快质子化变化。结合同源建模和量子力学/分子力学（QM/MM）几何优化，我们将质子化动力学分配给 Glu169 的超快去质子化，以及 Glu169 骨架的瞬态质子化，然后在几十皮秒的时间尺度上从骨架向 Asp299 的羧基转移质子。第二个质子转移与视黄醛动力学无关，反映了第一个光产物中的纯蛋白质变化。我们假设这些蛋白质动力学是导致通道导电性的蛋白质整体变化级联的第一步。
