Structural changes of sensory rhodopsin I and its transducer protein are dependent on the protonated state of Asp76
Structural changes of sensory rhodopsin I and its transducer protein are dependent on the protonated state of Asp76
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DOI：
10.1021/bi702050c
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发表时间：
2008-03-04
期刊：
影响因子：
2.9
通讯作者：
Kandori, Hideki
中科院分区：
文献类型：
--
作者：
Furutani, Yuji;Takahashi, Hazuki;Kandori, Hideki
感觉视紫红质I(SRI)在与盐杆菌转导蛋白I(HtrI)的复合体中发挥正、负趋光性的作用。橙色光激活SRI导致SRI的视黄亚甲基发色团去质子化，产生S-373光循环中间体，这是正趋光性的信号状态。在这项研究中，我们通过傅里叶变换红外光谱观察到S373中间体形成时两个分子之间的结构耦合对pH的依赖关系。在碱性pH下，当Asp76(质子化视黄基席夫碱的一个反离子)被去质子化时，依赖于HtrI的差异光谱的变化仅限于1661(+)/1647(-)cm(-1)处的酰胺I带的还原，而其中一个质子化的羧酸带的微扰发生在1734(-)cm-1处(它似乎只有在与Htrl络合时才变得电离)。然而，在酸性pH下，HtrI-络合物SRI不仅表现出光诱导的酰胺I变化的还原，而且还表现出更广泛的光谱变化，包括几个新的酰胺I带的出现，与生色团相关的振动模式的扰动，以及其他具有酪氨酸、谷氨酸和天冬氨酸残基特征的额外变化。由于在酸性条件下，SRI的D76N突变体的复合体没有观察到这种结构变化的pH依赖性，因此我们得出结论，只有当Asp76被中和时，SRI和Htrl之间才会发生广泛的橙光诱导构象偶联。
Sensory rhodopsin I (SRI) functions in both positive and negative phototaxis in complex with halobacterial transducer protein I (HtrI). Orange light activation of SRI results in deprotonation of the retinylidene chromophore of SRI to produce the S-373 photocycle intermediate, the signaling state for positive phototaxis. In this study, we observed pH dependence on structural coupling between the two molecules upon the formation of the S373 intermediate by means of Fourier transform infrared spectroscopy. At alkaline pH, where Asp76 (one of the counterions of the protonated retinylidene Schiff base) is deprotonated, HtrI-dependent alteration of the light-induced difference spectra is limited to reduction of amide I bands at 1661 (+)/ 1647 (-) cm(-1), and perturbation of one of the protonated carboxylic acid bands occurs at 1734 (-) cm-1 (which appears to become ionized only when complexed with Htrl). However, at acidic pH, HtrI-complexed SRI exhibits not only light-induced reduction of the amide I changes but a wider range of spectral alterations including the appearance of several new amide I bands, perturbation of the chromophore-related vibrational modes, and other additional changes characteristic of tyrosine, glutamate, and aspartate residues. Since such pH dependence of structural changes was not observed in the complex of the D76N mutant of SRI, which behaves much like HtrI-complexed SRI in acidic conditions, we conclude that extensive orange light-induced conformational coupling between SRI and Htrl occurs only when Asp76 is neutralized.