Low temperature FTIR spectroscopy provides new insights in the pH-dependent proton pathway of proteorhodopsin.
Low temperature FTIR spectroscopy provides new insights in the pH-dependent proton pathway of proteorhodopsin.
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低温 FTIR 光谱为原视紫红质 pH 依赖性质子途径提供了新的见解。
DOI：
10.1016/j.bbabio.2011.09.001
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
J. Wachtveitl
中科院分区：
文献类型：
--
作者：
Mirka;G. Schäfer;S. Shastri;I. Weber;C. Glaubitz;W. Mäntele;J. Wachtveitl
本文采用低温FTIR光谱对变形紫质的低pH光循环进行了广泛的研究。除了已知的全反式和13顺式视网膜振动特征外，在pH 5.1下的77K差谱在1744cm−1处显示了一个额外的负信号，这被解释为L状态的指示。随后的光循环步骤在高于200K的温度下进行了研究。可见光和红外光谱的结合使我们观察到，在酸性条件下，席夫碱的去质子化与新的质子受体Asp或Glu侧链的质子化相连。在Asp/Glu ν(C=O)振动谱区，后期中间体的差谱特征为较大的酰胺I变化和（−）1751cm−1/(+)1725cm-1两个谱带。负特征的带位置指向Asp-97的瞬态去质子化。此外，还研究了酸性光循环的pH依赖性。pH值5.5下的差异光谱显示出与关键残基质子化状态变化有关的明显差异。基于我们的数据，我们提出了一个三态模型来解释PR的复杂的pH依赖性。
In the presented study the low pH photocycle of proteorhodopsin is extensively investigated by means of low temperature FTIR spectroscopy. Besides the already well-known characteristics of the all-trans and 13-cis retinal vibrations the 77K difference spectrum at pH 5.1 shows an additional negative signal at 1744cm−1which is interpreted as indicator for the L state. The subsequent photocycle steps are investigated at temperatures higher than 200K. The combination of visible and FTIR spectroscopy enabled us to observe that the deprotonation of the Schiff base is linked to the protonation of an Asp or Glu side chain — the new proton acceptor under acidic conditions. The difference spectra of the late intermediates are characterized by large amide I changes and two further bands ((−)1751cm−1/(+)1725cm-1) in the spectral region of the Asp/Glu ν(C=O) vibrations. The band position of the negative signature points to a transient deprotonation of Asp-97. In addition, the pH dependence of the acidic photocycle was investigated. The difference spectra at pH 5.5 show distinct differences connected to changes in the protonation state of key residues. Based on our data we propose a three-state model that explains the complex pH dependence of PR.
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