Nuclear Magnetic Resonance Detection of Hydrogen Bond Network in a Proton Pump Rhodopsin RxR and Its Alteration during the Cyclic Photoreaction

• Published in: Journal of the American Chemical Society Vol. 145; no. 28; pp. 15295 - 15302
• Main Authors: Suzuki, Rika, Nagashima, Toshio, Kojima, Keiichi, Hironishi, Reika, Hirohata, Masafumi, Ueta, Tetsuya, Murata, Takeshi, Yamazaki, Toshio, Sudo, Yuki, Takahashi, Hideo
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 19.07.2023
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.3c02833

Hydrogen bond formation and deformation are crucial for the structural construction and functional expression of biomolecules. However, direct observation of exchangeable hydrogens, especially for oxygen-bound hydrogens, relevant to hydrogen bonds is challenging for current structural analysis approaches. Using solution-state NMR spectroscopy, this study detected the functionally important exchangeable hydrogens (i.e., Y49-ηOH and Y178-ηOH) involved in the pentagonal hydrogen bond network in the active site of R. xylanophilus rhodopsin (RxR), which functions as a light-driven proton pump. Moreover, utilization of the original light-irradiation NMR approach allowed us to detect and characterize the late photointermediate state (i.e., O-state) of RxR and revealed that hydrogen bonds relevant to Y49 and Y178 are still maintained during the photointermediate state. In contrast, the hydrogen bond between W75-εNH and D205-γCOO– is strengthened and stabilizes the O-state.