Temperature-Dependent Interactions between Photoactivated Pharaonis Phoborhodopsin and Its Transducer

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• 作者：Kentaro Kamada ; Yuji Furutani ; Yuki Sudo ; Naoki Kamo ; and Hideki Kandori
• 刊名：Biochemistry
• 出版年：2006
• 出版时间：April 18, 2006
• 年：2006
• 卷：45
• 期：15
• 页码：4859 - 4866
• 全文大小：254K
• 年卷期：v.45,no.15(April 18, 2006)
• ISSN：1520-4995

文摘

Pharaonis phoborhodopsin (ppR, also called pharaonis sensory rhodopsin II, psRII) is a receptorfor negative phototaxis in Natronomonas pharaonis. In membranes, it forms a 2:2 complex with itstransducer protein pHtrII, and the association is weakened by 2 orders of magnitude in the M intermediate(ppR_M). Such a change is believed to correspond to the transfer of the light signal to pHtrII. A previousFourier transform infrared (FTIR) study observed hydrogen-bonding alteration of Asn74 in pHtrII in theM state, suggesting a light-signaling pathway from the receptor to the transducer [Furutani, Y., Kamada,K., Sudo, Y., Shimono, K., Kamo, N., and Kandori, H. (2005) Biochemistry 44, 2909-2915]. In thispaper, we measure temperature dependence of the ppR_M minus ppR spectra in the absence and presenceof pHtrII at 250-293 K. Significant temperature dependence was observed for the amide-I vibrations ofhelices only for the ppR/pHtrII complex, where the amplitude of amide-I vibrations was reduced at roomtemperature. ¹³C-Labeling of ppR or pHtrII revealed that such spectral changes of helices originate fromppR and not pHtrII. The hydrogen-bonding alteration of Asn74 in pHtrII was temperature-independent,implying that the observed helical structural perturbation in ppR takes place in different region. On theother hand, temperature-dependent structural changes of helices were diminished for the complex of ppRwith the G83C and G83F mutants of pHtrII. Gly83 is believed to connect the transmembrane helix andcytosolic linker region in a flexible kink near the membrane surface of pHtrII, and its replacement by Cysor Phe abolishes the photosensory function. The present study provides direct experimental evidence thatGly83 plays an important structural role in the activation processes of the ppR/pHtrII complex. A molecularmechanism of protein structural changes in the ppR/pHtrII complex is discussed on the basis of the presentFTIR results.