School of Life Sciences, Tianjin University, Tianjin 300072, PR China; Tianjin Key Laboratory of Function and Application of Biological Macromolecular Structures, School of Life Sciences, Tianjin University, Tianjin 300072, PR China.
Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, 117543, Singapore.
Int J Biol Macromol. 2021 Jan 1;166:1141-1148. doi: 10.1016/j.ijbiomac.2020.10.269. Epub 2020 Nov 4.
Spider silk has remarkable physical and biocompatible properties. Investigation of structure-function relationship and self-assembly process of spidroins is necessary for uncovering the mechanism of silk fiber formation. Nevertheless, how the terminal domains initiate self-assembly of soluble tubuliform spidroins to form solid eggcase silk is still not fully understood. Here we investigate the roles of both terminal domains of tubuliform spidroin 1 (TuSp1) in the silk fiber formation. We found that interactions among the terminal domains drive rapid TuSp1 self-assembly and fiber formation, which is insensitive to pH changes from 6.0 to 7.0. These interactions also contribute to the spidroin chain alignment in fiber formation upon shear-force exposure. Structural analysis and site-directed mutagenesis identified eight critical surface-exposed residues involved in hydrophobic interactions among terminal domains. Spidroins with single-point mutations of these residues fail to form intermediate micelle-like structures. The structural docking model indicates that multiple terminal domains of TuSp1 may interact with each other based on hydrophobic interactions and surface complementarity, which may lead to forming the surface of the micelle-like structure. Our results provide new insights into the structural mechanism of eggcase silk formation and the basis for designing and producing novel biomaterials derived from spider eggcase silk.
蜘蛛丝具有显著的物理和生物相容性。研究丝蛋白的结构-功能关系和自组装过程对于揭示丝纤维形成的机制是必要的。然而，末端结构域如何启动可溶性管状丝蛋白的自组装形成固体卵壳丝仍未完全理解。在这里，我们研究了管状丝蛋白 1（TuSp1）的两个末端结构域在丝纤维形成中的作用。我们发现，末端结构域之间的相互作用驱动 TuSp1 的快速自组装和纤维形成，这对 pH 值在 6.0 到 7.0 之间的变化不敏感。这些相互作用也有助于在剪切力暴露下，丝蛋白链在纤维形成中的排列。结构分析和定点突变确定了 8 个关键的表面暴露残基，这些残基参与末端结构域之间的疏水相互作用。这些残基的单点突变会导致丝蛋白无法形成中间类似胶束的结构。结构对接模型表明，TuSp1 的多个末端结构域可能基于疏水相互作用和表面互补性相互作用，这可能导致形成胶束状结构的表面。我们的结果为卵壳丝形成的结构机制提供了新的见解，并为设计和生产源自蜘蛛卵壳丝的新型生物材料提供了基础。
