Site-specific orientation of an α-helical peptide ovispirin-1 from isotope-labeled SFG spectroscopy.
Site-specific orientation of an α-helical peptide ovispirin-1 from isotope-labeled SFG spectroscopy.
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DOI：
10.1021/jp408064b
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发表时间：
2013-11-27
期刊：
影响因子：
--
通讯作者：
Chen Z
中科院分区：
文献类型：
--
作者：
Ding B;Laaser JE;Liu Y;Wang P;Zanni MT;Chen Z
和频产生(SFG)振动光谱常被用来探测多肽表面的骨架结构和取向。利用Ovispirin-1多肽在聚苯乙烯的固/液界面上，首次证明SFG可以探测单个同位素标记残基的极化响应。为了解释光谱强度，我们用激子哈密顿方法模拟了光谱。我们表明，单独的标记或未标记的酰胺I带的偏振相关性并不能提供足够的结构约束来获得Ovispirin螺旋在固/液界面上的倾斜和扭曲，但这两者都可以根据整个光谱的偏振相关性来确定。对于Ovispirin，对偏振SFG实验数据的详细分析表明，螺旋轴大约与表面法线倾斜138度，同位素标记的C=O基团的跃迁偶极子与表面法线倾斜23度，疏水区域面向聚苯乙烯表面。我们进一步证明了哈密顿方法能够处理耦合效应和结构无序。为了进行比较，我们还收集了类似条件下Ovispirin的FTIR光谱，这表明SFG对于单层多肽表面的结构研究具有更高的灵敏度。我们的研究揭示了结构和环境效应是如何出现在酰胺I带的SFG谱中的，并确立了同位素标记多肽的SFG将是一种强大的技术，可以用逐个残基的分辨率来阐明二级结构。
Sum-frequency generation (SFG) vibrational spectroscopy is often used to probe the backbone structures and orientations of polypeptides at surfaces. Using the ovispirin-1 polypeptide at the solid/liquid interface of polystyrene, we demonstrate for the first time that SFG can probe the polarization response of a single isotope labeled residue. To interpret the spectral intensities, we simulated the spectra using an excitonic Hamiltonian approach. We show that the polarization dependence of either the label or the unlabeled amide I band alone does not provide sufficient structural constraints to obtain both the tilt and the twist of the ovispirin helix at a solid/liquid interface, but that both can be determined from the polarization dependence of the complete spectrum. For ovispirin, the detailed analysis of the polarized SFG experimental data shows that the helix axis is tilted at roughly 138 degrees from the surface normal, and the transition dipole of the isotope labeled C=O group is tilted at 23 degrees from the surface normal, with the hydrophobic region facing the polystyrene surface. We further demonstrated that the Hamiltonian approach is able to address the coupling effect and the structural disorder. For comparison, we also collected the FTIR spectrum of ovispirin under similar conditions, which reveals the enhanced sensitivity of SFG for structural studies of single monolayer peptide surfaces. Our study provides insight into how structural and environmental effects appear in SFG spectra of the amide I band and establishes that SFG of isotope labeled peptides will be a powerful technique for elucidating secondary structures with residue-by-residue resolution.
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