His166 Is the Schiff Base Proton Acceptor in Attractant Phototaxis Receptor Sensory Rhodopsin I

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• 作者：Jun Sasaki ; Hazuki Takahashi ; Yuji Furutani ; Oleg A. Sineshchekov ; John L. Spudich ; Hideki Kandori
• 刊名：Biochemistry
• 出版年：2014
• 出版时间：September 23, 2014
• 年：2014
• 卷：53
• 期：37
• 页码：5923-5929
• 全文大小：351K
• ISSN：1520-4995

文摘

Photoactivation of attractant phototaxis receptor sensory rhodopsin I (SRI) in Halobacterium salinarum entails transfer of a proton from the retinylidene chromophore鈥檚 Schiff base (SB) to an unidentified acceptor residue on the cytoplasmic half-channel, in sharp contrast to other microbial rhodopsins, including the closely related repellent phototaxis receptor SRII and the outward proton pump bacteriorhodopsin, in which the SB proton acceptor is an aspartate residue salt-bridged to the SB in the extracellular (EC) half-channel. His166 on the cytoplasmic side of the SB in SRI has been implicated in the SB proton transfer reaction by mutation studies, and mutants of His166 result in an inverted SB proton release to the EC as well as inversion of the protein鈥檚 normally attractant phototaxis signal to repellent. Here we found by difference Fourier transform infrared spectroscopy the appearance of Fermi-resonant X鈥揌 stretch modes in light-minus-dark difference spectra; their assignment with ¹⁵N labeling and site-directed mutagenesis demonstrates that His166 is the SB proton acceptor during the photochemical reaction cycle of the wild-type SRI鈥揌trI complex.