Conformational analysis of XA and AX dipeptides in water by electronic circular dichroism and 1H NMR spectroscopy.
Conformational analysis of XA and AX dipeptides in water by electronic circular dichroism and 1H NMR spectroscopy.
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通过电子圆二色性和 1H NMR 光谱对水中的 XA 和 AX 二肽进行构象分析。
DOI：
10.1021/jp0561625
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
Schweitzer-Stenner,Reinhard
中科院分区：
文献类型：
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作者：
Hagarman,Andrew;Measey,Thomas;Doddasomayajula,RaviS;Dragomir,Isabelle;Eker,Fatma;Griebenow,Kai;Schweitzer-Stenner,Reinhard
我们测量了AX、XA和XG在D2O中的变温电子圆二色谱(ECD)。所有的XA和AX多肽的光谱都显示了大量的多脯氨酸II(PPII)构象，而LG、KG、PG和AG的ECD光谱被发现与基于丙氨酸的二肽有定量的不同。另外的紫外吸收数据表明，XG多肽的ECD光谱来自于多肽和C-末端基团之间的电子耦合，并且光谱差异反映了后者的不同取向。我们还测量了所研究的二肽的~1H核磁共振谱，以确定C-末端残基的3JHα氨偶联常数。用包含PPII和类α构象的两态模型分析了观测到的电子捕获光谱的温度依赖关系和相应的室温3JHβNH耦合常数。XA系列中丙氨酸的PPII倾向仅受N-末端侧链的轻微调制，且大于50%。与AA相比，含有L、P、S、KV、E、T和I的XA肽都能使扩展的β链构象相对稳定。XA多肽的PPII组分在AA的0.64和DA的0.58之间变化，而AX多肽的PPII组分则低得多。从所研究的AX多肽中，只有AL和AQ显示出预期的PPII倾向。我们发现AT、AI和AV明显更喜欢扩展的β-链构象。对Aa、Aaa和Aaaa的定量比较揭示了PPII种群的AAAa和AAa；Aaa≈Aa，与MD计算和拉曼光学活性研究的结果一致(McColl等人J.Am化学。编号2004、126、5076)。
We measured the temperature-dependent electronic circular dichroism (ECD) spectra of AX, XA, and XG dipeptides in D2O. The spectra of all XA and AX peptides indicate a substantial population of the polyproline II (PPII) conformation, while the ECD spectra of LG, KG, PG, and AG were found to be quantitatively different from the alanine-based dipeptides. Additional UV absorption data indicate that the ECD spectra of the XG peptides stem from electronic coupling between the peptide and the C-terminal group, and that spectral differences reflect different orientations of the latter. We also measured the1H NMR spectra of the investigated dipeptides to determine the3JHαNHcoupling constants for the C-terminal residue. The observed temperature dependence of the ECD spectra and the respective room-temperature3JHαNHcoupling constants were analyzed by a two-state model encompassing PPII and a β-like conformation. The PPII propensity of alanine in the XA series is only slightly modulated by the N-terminal side chain, and is larger than 50%. As compared to AA, XA peptides containing L, P, S, K V, E, T, and I all cause a relative stabilization of the extended β-strand conformation. The PPII fractions of XA peptides varied between 0.64 for AA and 0.58 for DA, whereas the PPII fractions of AX peptides were much lower. From the investigated AX peptides, only AL and AQ showed the expected PPII propensity. We found that AT, AI, and AV clearly prefer an extended β-strand conformation. A quantitative comparison of AA, AAA, and AAAA revealed a hierarchy AAAA > AAA ≈ AA for the PPII population, in agreement with predictions from MD calculations and results from Raman optical activity studies (McColl et al.J. Am. Chem. Soc.2004,126, 5076).