Assignment of the Hydrogen-Out-Of-Plane and -in-Plane Vibrations of the Retinal Chromophore in the K Intermediate of pharaonis Phoborhodopsin

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• 作者：Yuji Furutani ; Yuki Sudo ; Akimori Wada ; Masayoshi Ito ; Kazumi Shimono ; Naoki Kamo ; Hideki Kandori
• 刊名：Biochemistry
• 出版年：2006
• 出版时间：October 3, 2006
• 年：2006
• 卷：45
• 期：39
• 页码：11836 - 11843
• 全文大小：170K
• 年卷期：v.45,no.39(October 3, 2006)
• ISSN：1520-4995

文摘

pharaonis phoborhodopsin (ppR; also called pharaonis sensory rhodopsin II, psR-II) is aphotoreceptor protein for negative phototaxis in Natronomonas pharaonis. Photoisomerization of the retinalchromophore from all-trans to 13-cis initiates conformational changes of the protein leading to activationof the cognate transducer protein (pHtrII). Elucidation of the initial photoreaction, formation of the Kintermediate of ppR, is important for understanding the mechanism of storage of photon energy. We havereported the K minus ppR Fourier transform infrared (FTIR) spectra, including several vibrational bandsof the retinal, the protein, and internal water molecules. It is interesting that more vibrational bands wereobserved in the hydrogen-out-of-plane (HOOP) region than for the light-driven proton pump, bacteriorhodopsin. This result implied that the steric constraints on the retinal chromophore in the binding pocketof ppR are distributed more widely upon formation of the initial intermediate. In this study, we assignedthe HOOP and hydrogen-in-plane vibrations by means of low-temperature FTIR spectroscopy applied toppR reconstituted with retinal deuterated at C7, C8, C10-C12, C14, and C15. As a result, the 966 (+)/971 (-) and 958 (+)/961 (-) cm^-1 bands were assigned to the C7=C8 and C11=C12 Au HOOP modes,respectively, suggesting that the structural changes spread to the middle part of the retinal. The positivebands at 1001, 994, 987, and 979 cm^-1 were assigned to the C15-HOOP vibrations of the K intermediate,whose frequencies are similar to those of the K_L intermediate of bacteriorhodopsin trapped at 135 K.Another positive band at 864 cm^-1 was assigned to the C14-HOOP vibration. Relatively many positivebands of hydrogen-in-plane vibrations supported the wide distribution of structural changes of the retinalas well. These results imply that the light energy was stored mainly in the distortions around the Schiffbase region while some part of the energy was transferred to the distal part of the retinal.