Department of Biotechnology, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan.
School of Biosciences, University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK.
Int J Biol Macromol. 2023 Aug 1;245:125537. doi: 10.1016/j.ijbiomac.2023.125537. Epub 2023 Jun 26.
Silk fibroin (SF) fiber from the silkworm Bombyx mori in the Silk II form has been used as an excellent textile fiber for over 5000 years. Recently it has been developed for a range of biomedical applications. Further expansion of these uses builds on the excellent mechanical strength of SF fiber, which derives from its structure. This relationship between strength and SF structure has been studied for over 50 years, but it is still not well understood. In this review, we report the use of solid-state NMR to study stable-isotope labeled SF fiber and stable-isotope labeled peptides including (Ala-Gly) and (Ala-Gly-Ser-Gly-Ala-Gly) as models of the crystalline fraction. We show that the crystalline fraction is a lamellar structure with a repetitive folding using β-turns every eighth amino acid, and that the sidechains adopt an antipolar arrangement rather than the more well-known polar structure described by Marsh, Corey and Pauling (that is, the Ala methyls in each layer point in opposite directions in alternate strands). The amino acids Ser, Tyr and Val are the next most common in B. mori SF after Gly and Ala, and occur in the crystalline and semi-crystalline regions, probably defining the edges of the crystalline region. Thus, we now have an understanding of the main features of Silk II but there is still a long way to go.
蚕丝素（SF）纤维来自桑蚕 Bombyx mori 的 Silk II 结构，已经作为一种优秀的纺织纤维使用了超过 5000 年。最近，它已经被开发用于一系列生物医学应用。这些用途的进一步扩展是基于 SF 纤维的优异机械强度，这源于其结构。SF 结构与强度之间的关系已经研究了超过 50 年，但仍未得到很好的理解。在这篇综述中，我们报告了使用固态 NMR 研究稳定同位素标记的 SF 纤维和稳定同位素标记的肽，包括（Ala-Gly）和（Ala-Gly-Ser-Gly-Ala-Gly），作为结晶部分的模型。我们表明，结晶部分是一种层状结构，使用β-转角每隔第八个氨基酸重复折叠，侧链采用反极性排列，而不是 Marsh、Corey 和 Pauling 描述的更为人熟知的极性结构（即，每个层中的 Ala 甲基指向相反方向的交替链）。丝氨酸、酪氨酸和缬氨酸是继甘氨酸和丙氨酸之后在桑蚕丝素中第二常见的氨基酸，存在于结晶区和半结晶区，可能定义了结晶区的边界。因此，我们现在对 Silk II 的主要特征有了一定的了解，但仍有很长的路要走。
