Tsujimura Masaki, Tamura Hiroyuki, Saito Keisuke, Ishikita Hiroshi
Department of Advanced Interdisciplinary Studies, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan.
Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan.
iScience. 2022 Apr 13;25(5):104247. doi: 10.1016/j.isci.2022.104247. eCollection 2022 May 20.
In low-barrier hydrogen bonds (H-bonds), the p values for the H-bond donor and acceptor moieties are nearly equal, whereas the redox potential values depend on the H position. Spectroscopic details of low-barrier H-bonds remain unclear. Here, we report the absorption wavelength along low-barrier H-bonds in protein environments, using a quantum mechanical/molecular mechanical approach. Low-barrier H-bonds form between Glu46 and -coumaric acid (CA) in the intermediate pR state of photoactive yellow protein and between Asp116 and the retinal Schiff base in the intermediate M-state of the sodium-pumping rhodopsin KR2. The H displacement of only ∼0.4 Å, which does not easily occur without low-barrier H-bonds, is responsible for the ∼50 nm-shift in the absorption wavelength. This may be a basis of how photoreceptor proteins have evolved to proceed photocycles using abundant protons.
在低势垒氢键（H键）中，H键供体和受体部分的p值几乎相等，而氧化还原电位值取决于H的位置。低势垒H键的光谱细节仍不清楚。在这里，我们使用量子力学/分子力学方法报告了蛋白质环境中沿低势垒H键的吸收波长。在光活性黄色蛋白的中间pR状态下，Glu46与香豆酸（CA）之间形成低势垒H键；在钠泵视紫红质KR2的中间M状态下，Asp116与视黄醛席夫碱之间形成低势垒H键。仅约0.4 Å的H位移（若无低势垒H键则不易发生）导致吸收波长发生约50 nm的位移。这可能是光感受器蛋白如何利用丰富的质子进行光循环进化的基础。
