Parallel β-Sheet Structure of Alanine Tetrapeptide in the Solid State As Studied by Solid-State NMR Spectroscopy

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• 作者：Tetsuo Asakura ; Kumiko Horiguchi ; Akihiro Aoki ; Yugo Tasei ; Akira Naito
• 刊名：Journal of Physical Chemistry B
• 出版年：2016
• 出版时间：September 1, 2016
• 年：2016
• 卷：120
• 期：34
• 页码：8932-8941
• 全文大小：624K
• 年卷期：0
• ISSN：1520-5207

文摘

The structural analysis of alanine oligopeptides is important for understanding the crystalline region in silks from spiders and wild silkworms and also the mechanism of cellular toxicity of human diseases arising from expansion in polyalanine sequences. The atomic-level structures of alanine tripeptide and tetrapeptide with antiparallel β-sheet structures (AP-Ala₃ and AP-Ala₄, respectively) together with alanine tripeptide with parallel β-sheet structures (P-Ala₃) have been determined, but alanine tetrapeptide with a parallel β-sheet structure (P-Ala₄) has not been reported yet. In this article, first, we established the preparation protocol of P-Ala₄ from more stable AP-Ala₄. Second, complete assignments of the ¹³C, ¹⁵N, and ¹H solid-state NMR spectra were performed with ¹³C- and ¹⁵N-labeled Ala₄ samples using several solid-state NMR techniques. Then, the structural constraints were obtained, for example, the amide proton peaks of P-Ala₄ in the ¹H double-quantum magic-angle spinning NMR spectrum were heavily overlapped and observed at about 7.4 ppm, which was a much higher field than that of 8.7–9.1 ppm observed for AP-Ala₄, indicating that the intermolecular hydrogen-bond lengths across strands (N–H···O═C) were considerably longer for P-Ala₄, that is, 2.21–2.34 Å, than those reported for AP-Ala₄, that is, 1.8–1.9 Å. The structural model was proposed for P-Ala₄ by NMR results and MD calculations.