State Key Laboratory of Silkworm Genome Biology, Key Laboratory of Sericultural Biology and Genetic Breeding, Ministry of Agriculture, Southwest University, Chongqing 400716, PR China.
Guangxi Research Academy of Seficultural Science, Nanning 530007, Guangxi, PR China.
Int J Biol Macromol. 2021 Feb 1;169:473-479. doi: 10.1016/j.ijbiomac.2020.12.132. Epub 2020 Dec 20.
Fibroin of the silkworm consists of fibroin heavy chain (Fib-H) with hydrophobic intermediate repeats flanked by hydrophilic N and C terminal domains (NTD and CTD, respectively), fibroin light chain (Fib-L), and P25. However, the respective roles of each polypeptide in silk processing remain largely unknown. Here, a series of transgenic silkworms with different fusion gene expression cassettes were created in order to selectively express different fluorescent fusion proteins in silk glands. The roles of different components in silk processing were investigated via observing and analyzing the movement and distribution of these proteins in the silk gland and in cocoon silk. The data showed that hydrophilic NTDs were distributed on the surface of micelles, providing sufficient electrostatic repulsion to prevent premature crystallization of silk proteins. Hydrophilic CTD==Ls ("==" represents the disulfide bond) were located on the inner layer of micelles to control the solubility of large micelles. The results presented here elucidated the underlying mechanisms of silkworm silk processing in vivo. This is significant for the development of artificial spinning technology, novel silk biomaterials, and silk gland expression systems.
家蚕丝由丝素重链（Fib-H）组成，其疏水的中间重复序列被亲水的 N 端和 C 端结构域（NTD 和 CTD）所包围，还包含丝素轻链（Fib-L）和 P25。然而，每种多肽在家蚕丝加工过程中的具体作用在很大程度上仍不清楚。在这里，我们构建了一系列携带不同融合基因表达盒的转基因家蚕，以便在丝腺中选择性表达不同的荧光融合蛋白。通过观察和分析这些蛋白在家蚕腺体和茧丝中的运动和分布，研究了不同成分在家蚕丝加工过程中的作用。结果表明，亲水的 NTD 分布在胶束的表面，提供了足够的静电排斥力，以防止丝蛋白过早结晶。亲水的 CTD-Ls（“=”表示二硫键）位于胶束的内层，以控制大胶束的溶解度。本研究阐明了家蚕体内丝加工的潜在机制，这对于人工纺丝技术、新型丝生物材料和丝腺表达系统的发展具有重要意义。
