Uncoupled peptide bond vibrations in α-helical and polyproline II conformations of polyalanine peptides
Uncoupled peptide bond vibrations in α-helical and polyproline II conformations of polyalanine peptides
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DOI：
10.1021/jp0460442
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发表时间：
2005-02-24
影响因子：
3.3
通讯作者：
Asher, SA
中科院分区：
文献类型：
--
作者：
Mikhonin, AV;Asher, SA
我们检查了不同 H2O/D2O 混合物中聚脯氨酸 II (PPII) 和 21 个残基主要是丙氨酸肽 (AP) 的 α 螺旋态的 204 nm 紫外共振拉曼 (UVR) 光谱。我们的假设是，如果酰胺主链振动耦合，则酰胺 N 的部分氘化将扰乱酰胺频率和拉曼截面，因为耦合将被中断；部分氘化衍生物的光谱不会简单地是完全质子化和氘化肽的总和。我们发现PPII构象和α-螺旋构象的AmIII和AmII'带的UVR光谱（以及PPII AmI、AmI'和AmII带）可以精确地建模为完全N-H质子化肽和N-D氘化肽的线性和。相邻肽键之间的这些振动发生的耦合可以忽略不计。因此，我们得出结论，这些肽键拉曼带可以被认为是被各个肽键独立地散射的拉曼。这极大地简化了这些振动带在肽和蛋白质结构的红外和拉曼研究中的使用。相反，α-螺旋构象的 AmI 和 AmI' 带不能很好地建模为完全 N-H 质子化和 N-D 氘化衍生物的线性和。这些带显示了相邻肽键振动之间耦合的证据。在利用AmI和AmI'带监测α-螺旋构象时必须小心，因为这些带可能随着α-螺旋长度的变化和主链构象的扰动而改变。
We examined the 204-nm UV resonance Raman (UVR) spectra of the polyproline II (PPII) and alpha-helical states of a 21-residue mainly alanine peptide (AP) in different H2O/D2O mixtures. Our hypothesis is that if the amide backbone vibrations are coupled, then partial deuteration of the amide N will perturb the amide frequencies and Raman cross sections since the coupling will be interrupted; the spectra of the partially deuterated derivatives will not simply be the sum of the fully protonated and deuterated peptides. We find that the UVR spectra of the AmIII and AmII' bands of both the PPII conformation and the alpha-helical conformation (and also the PPII AmI, AmI', and AmII bands) can be exactly modeled as the linear sum of the fully N-H protonated and N-D deuterated peptides. Negligible coupling occurs for these vibrations between adjacent peptide bonds. Thus, we conclude that these peptide bond Raman bands can be considered as being independently Raman scattered by the individual peptide bonds. This dramatically simplifies the use of these vibrational bands in IR and Raman studies of peptide and protein structure. In contrast, the AmI and AmI' bands of the alpha-helical conformation cannot be well modeled as a linear sum of the fully N-H protonated and N-D deuterated derivatives. These bands show evidence of coupling between adjacent peptide bond vibrations. Care must be taken in utilizing the AmI and AmI' bands for monitoring a.-helical conformations since these bands are likely to change as the alpha-helical length changes and the backbone conformation is perturbed.