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

作者：Suzuki Yu; Yamazaki Toshimasa; Aoki Akihiro; Shindo Heisaburo; Asakura Tetsuo^*

来源：Biomacromolecules, 2014, 15(1): 104-112.

DOI：10.1021/bm401346h

The silk fibroin stored in the silk gland of the Bombyx mori silkworm, called %26quot;liquid silk%26quot;, 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 beta-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 %26quot;liquid silk%26quot; 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 C-13, N-15, and H-1 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 C-13 alpha, C-13 beta, (CO)-C-13, H-1 alpha, (HN)-H-1, and N-15 chemical shifts. The twenty-five best matches of torsion angles (phi, phi) were well populated and mainly fell into the regions for typical type II beta-turn structures in the (phi, phi) map for the GAGXGA (X = S, Y, V) motifs. In contrast, (phi, phi) plots for motif GAASGA were scattered, indicating that the motif is in a disordered structure. Furthermore, inter-residue HN-H alpha 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 beta-turn structure. Thus, we could show the presence of the repeated type II beta-turn structure in %26quot;liquid silk%26quot;.

• 出版日期2014-1