NMR Study of the Structures of Repeated Sequences, GAGXGA (X = S, Y, V), in Bombyx mori Liquid Silk

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• 作者：Yu Suzuki ; Toshimasa Yamazaki ; Akihiro Aoki ; Heisaburo Shindo ; Tetsuo Asakura
• 刊名：Biomacromolecules
• 出版年：2014
• 出版时间：January 13, 2014
• 年：2014
• 卷：15
• 期：1
• 页码：104-112
• 全文大小：530K
• ISSN：1526-4602

文摘

The silk fibroin stored in the silk gland of the Bombyx mori silkworm, called 鈥渓iquid silk鈥? is spun out and converted into the silk fiber with extremely high strength and high toughness. Therefore it is important to determine the silk structure before spinning called Silk I at an atomic level to clarify the fiber formation mechanism. We proposed the repeated type II 尾-turn structure as Silk I in the solid state with the model peptide (AG)₁₅ and several solid state NMR techniques previously. In this paper, the solution structure of native 鈥渓iquid silk鈥?was determined with solution NMR, especially for tandem repeated sequences with (GAGXGA)_n (X = S, Y, V) and GAASGA motifs in the B. mori silk fibroin. The assignment of the ¹³C, ¹⁵N, and ¹H solution NMR spectra for the repetitive sequence motifs was achieved, and the chemical shifts were obtained. The program, TALOS-N, to predict the backbone torsion angles from the chemical shifts of proteins was applied to these motifs with ¹³C伪, ¹³C尾, ¹³CO, ¹H伪, ¹HN, and ¹⁵N chemical shifts. The twenty-five best matches of torsion angles (, 蠁) were well populated and mainly fell into the regions for typical type II 尾-turn structures in the (, 蠁) map for the GAGXGA (X = S, Y, V) motifs. In contrast, (, 蠁) plots for motif GAASGA were scattered, indicating that the motif is in a disordered structure. Furthermore, inter-residue HN-H伪 NOE cross peaks between i-th and (i+2)th residues in GAGXGA (X = S, Y, V) motifs were observed, supporting the repeated type II 尾-turn structure. Thus, we could show the presence of the repeated type II 尾-turn structure in 鈥渓iquid silk鈥?