Steric Constraint in the Primary Photoproduct of Sensory Rhodopsin II Is a Prerequisite for Light-Signal Transfer to HtrII

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• 作者：Motohiro Ito ; Yuki Sudo ; Yuji Furutani ; Takashi Okitsu ; Akimori Wada ; Michio Homma ; John L. Spudich ; Hideki Kandori
• 刊名：Biochemistry
• 出版年：2008
• 出版时间：June 10, 2008
• 年：2008
• 卷：47
• 期：23
• 页码：6208 - 6215
• 全文大小：1738K
• 年卷期：v.47,no.23(June 10, 2008)
• ISSN：1520-4995

文摘

Sensory rhodopsin II (SRII, also called pharaonis phoborhodopsin, ppR) is responsible for negative phototaxis in Natronomonas pharaonis. Photoisomerization of the retinal chromophore from all-trans to 13-cis initiates conformational changes in the protein, leading to activation of the cognate transducer protein (HtrII). We previously observed enhancement of the C₁₄−D stretching vibration of the retinal chromophore at 2244 cm⁻¹ upon formation of the K state and interpreted that a steric constraint occurs at the C₁₄D group in SRII_K. Here, we identify the counterpart of the C₁₄D group as Thr204, because the C₁₄−D stretching signal disappeared in T204A, T204S, and T204C mutants as well as a C₁₄−HOOP (hydrogen out-of-plane) vibration at 864 cm⁻¹. Although the K state of the wild-type bacteriorhodopsin (BR), a light-driven proton pump, possesses neither 2244 nor 864 cm⁻¹ bands, both signals appeared for the K state of a triple mutant of BR that functions as a light sensor (P200T/V210Y/A215T). We found a positive correlation between these vibrational amplitudes of the C₁₄ atom at 77 K and the physiological phototaxis response. These observations strongly suggest that the steric constraint between the C₁₄ group of retinal and Thr204 of the protein is a prerequisite for light-signal transduction by SRII.