In Situ Misfolding of Human Islet Amyloid Polypeptide at Interfaces Probed by Vibrational Sum Frequency Generation
In Situ Misfolding of Human Islet Amyloid Polypeptide at Interfaces Probed by Vibrational Sum Frequency Generation
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DOI：
10.1021/ja909546b
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发表时间：
2010-04-21
影响因子：
15
通讯作者：
Yan, Elsa C. Y.
中科院分区：
文献类型：
--
作者：
Fu, Li;Ma, Gang;Yan, Elsa C. Y.
蛋白质在界面处构象变化的动力学分析对于理解膜表面的许多生物过程至关重要。在这项研究中，我们表明，表面选择性和频产生（SFG）光谱可以用来调查在接口处的蛋白质的构象变化的动力学。我们专注于一种内在无序的蛋白质，人胰岛淀粉样多肽（hIAPP），这是已知的错误折叠成β-折叠结构后，与膜的相互作用。使用ssp偏振设置（s-偏振SFG，s-偏振可见光，和p-偏振红外），我们观察到的变化后，在空气/水界面的hIAPP的酰胺I光谱的二棕榈酰磷酸甘油（DPPG），对应于脂质诱导的二级结构的变化。我们还使用了手性敏感的psp偏振设置来获得酰胺I光谱，并观察到手性结构的逐渐积累，显示出平行β-折叠的振动特性。我们推测，在1622 cm（-1）处平行β折叠的反对称拉伸频率处的二阶手性光学响应可能是β折叠聚集体的高度特征性光学性质，不仅对于hIAPP，而且可能对于其他淀粉样蛋白。分析非手性和手性酰胺I光谱，我们得出结论，DPPG诱导hIAPP从α-螺旋和无规卷曲结构的空气/水界面的平行β-折叠结构的错误折叠。我们建议，SFG可以补充现有的技术，在获得动力学和结构信息探测蛋白质的结构和功能的接口。
Kinetic analysis of conformational changes of proteins at interfaces is crucial for understanding many biological processes at membrane surfaces. In this study, we demonstrate that surface-selective sum frequency generation (SFG) spectroscopy can be used to investigate kinetics of conformational changes of proteins at interfaces. We focus on an intrinsically disordered protein, human islet amyloid polypeptide (hIAPP) that is known to misfold into the beta-sheet structure upon interaction with membranes. Using the ssp polarization setting (s-polarized SFG, s-polarized visible, and p-polarized infrared), we observe changes in the amide I spectra of hIAPP at the air/water interface after addition of dipalmitoylphosphoglycerol (DPPG) that correspond to the lipid-induced changes in secondary structures. We also used the chiral-sensitive psp polarization setting to obtain amide I spectra and observed a gradual buildup of the chiral structures that display the vibrational characteristics of parallel beta-sheets. We speculate that the second-order chiral-optical response at the antisymmetric stretch frequency of parallel beta-sheet at 1622 cm(-1) could be a highly characteristic optical property of the beta-sheet aggregates not only for hIAPP, but possibly also for other amyloid proteins. Analyzing the achiral and chiral amide I spectra, we conclude that DPPG induces the misfolding of hIAPP from alpha-helical and random-coil structures to the parallel beta-sheet structure at the air/water interface. We propose that SFG could complement existing techniques in obtaining kinetic and structural information for probing structures and functions of proteins at interfaces.