Distortion of the amide-I and -II bands of an α-helical membrane protein, pharaonis halorhodopsin, depends on thickness of gold films utilized for surface-enhanced infrared absorption spectroscopy
Distortion of the amide-I and -II bands of an α-helical membrane protein, pharaonis halorhodopsin, depends on thickness of gold films utilized for surface-enhanced infrared absorption spectroscopy
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DOI：
10.1016/j.chemphys.2012.11.011
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发表时间：
2013-06-20
期刊：
影响因子：
2.3
通讯作者：
Furutani, Yuji
中科院分区：
文献类型：
--
作者：
Guo, Hao;Kimura, Tetsunari;Furutani, Yuji
衰减全反射表面增强红外吸收 (ATR-SEIRA) 是在单层水平探索膜蛋白分子机制的有力工具。然而，正如对紧邻表面的小分子所观察到的那样，带强度、位置和方向在很大程度上受到金薄膜的存在的影响。在这里，我们研究了α螺旋膜蛋白法老视紫红质（pHR）对带形状的影响，该蛋白通过六组氨酸标签和镍三乙酸（Ni-NTA）连接体之间的复合物形成附着在金表面上。随着膜厚度的增加，观察到酰胺-I 和-II 带的正常、双极和倒置形状，尽管 pHR 分子会远离表面。这种有趣现象的物理起源已经通过改变入射角、偏振和薄膜沉积速率来确定。我们发现观察到的吸收异常是由于垂直偏振光的影响。此外，结果表明，在渗滤阈值以下，带形状是正常的，当薄膜的反常吸收较强时，会出现双极带形状，而当表面散射占主导地位的薄膜时，会出现倒置的带形状。 (C) 2012 Elsevier B.V. 保留所有权利。
Surface-enhanced infrared absorption with attenuated total reflection (ATR-SEIRA) is a powerful tool for exploring molecular mechanisms of membrane proteins at the monolayer level. However, the band intensity, position, and direction can be largely influenced by the presence of a thin gold film, as observed for small molecules existing in close proximity to the surface. Here we investigated influence on the band shapes of an a-helical membrane protein, pharaonis halorhodopsin (pHR), attached on the gold surface through a complex formation between a six-histidines tag and a Ni-nitrilotriacetic acid (Ni-NTA) linker. Normal, bipolar, and inverted shapes of amide-I and -II bands were observed with an increase in film thickness, although pHR molecules would locate relatively far from the surface. The physical origin of this interesting phenomenon has been identified by changing incident angle, polarization, and film deposition rate. We find that the observed absorption anomalies are due to the influence of perpendicularly polarized light. Furthermore, it is shown that the band shapes are normal below the percolation threshold, and bipolar ones occur when an anomalous absorption by the films is strong, while the inverted ones develop with films in which surface scattering is predominant. (C) 2012 Elsevier B.V. All rights reserved.