Nature of vibrational coupling in helical peptides: An isotopic labeling study
Nature of vibrational coupling in helical peptides: An isotopic labeling study
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DOI：
10.1021/ja037998t
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发表时间：
2004-03-03
影响因子：
15
通讯作者：
Keiderling, TA
中科院分区：
文献类型：
--
作者：
Huang, R;Kubelka, J;Keiderling, TA
对前人研究过的Ac(AAAAK)(4)AAAAY-NH2序列的25个残基进行了红外（IR）和振动圆二色性（VCD）测量。利用密度泛函理论（DFT）对AcA(10)-NHCH3的性质张量转移，对相应的同位素标记的a- a (24)-NHCH3进行了理论IR和VCD模拟。模拟预测和实验证实了i， i + 1和i， i + 2残基之间的振动耦合常数在符号上不同，从而导致C-13 VCD模式的逆转，并解释了之前文章中报道的C-13酰胺i频率的大位移。对于较大的标签分离（i、i + 4除外）和较多的标签均匀分离，耦合常数的符号保持一致。这些效应证实，同位素标记的基团的振动基本上只是相互耦合的，而与未标记的基团的振动有效地解耦。这一发展证实了同位素标记在振动谱研究特定位点结构方面的效用。观察到的光谱效应不能仅仅通过考虑酰胺振子之间的跃迁偶极子耦合（TDC）来解释，特别是对于较小的标签分离，但是TDC和从头算预测的耦合在大分离时大致收敛。
Infrared (IR) and vibrational circular dichroism (VCD) spectra were measured for a series of isotopically (C-13 on two or more amide C=O) labeled, 25 residue, a-helical peptides of the sequence Ac(AAAAK)(4)AAAAY-NH2 that were also studied in the previous paper. Theoretical IR and VCD simulations were performed for correspondingly isotopically labeled Ac-A(24)-NHCH3 constrained to an a-helical conformation by use of property tensor transfer from density functional theory (DFT) calculations on AcA(10)-NHCH3. The simulations predicted and experiments confirmed that the vibrational coupling constants between i, i + 1 and i, i + 2 residues differ in sign, thus leading to a reversal of the C-13 VCD pattern and explaining the large shift in the C-13 amide I frequency as reported in the previous paper. The sign of the coupling constant remained consistent for larger label separation (with the exception of i, i + 4) and for more labels with uniform separation. Such effects confirm that the isotopically labeled group vibrations are essentially only coupled to each other and are effectively uncoupled from those of the unlabeled groups. This development confirms the utility of isotopic labels for site-specific structural studies with vibrational spectra. Observed spectral effects cannot be explained by considering only transition dipole coupling (TDC) between amide oscillators, particularily for smaller label separations, but the TDC and ab initio predicted couplings roughly converge at large separation.