Multiscale mechanisms of nutritionally induced property variation in spider silks

Variability in spider major ampullate (MA) silk properties at different scales has proven difficult to determine and remains an obstacle to the development of synthetic fibers mimicking MA silk performance. A multitude of techniques may be used to measure multiscale aspects of silk properties. Here we fed five species of Araneoid spider solutions that either contained protein or were protein deprived and performed silk tensile tests, small and wide-angle X-ray scattering (SAXS/WAXS), amino acid composition analyses, and silk gene expression analyses, to resolve persistent questions about how nutrient deprivation induces variations in MA silk mechanical properties across scales. Our analyses found that the properties of each spider’s silk varied differently in response to variations in their protein intake. We found changes in the crystalline and non-crystalline nanostructures to play specific roles in inducing the property variations we found. Across treatment MaSp expression patterns differed in each of the five species. We found that in most species MaSp expression and amino acid composition variations did not conform with our predictions based on a traditional MaSp expression model. In general, changes to the silk’s alanine and proline compositions influenced the alignment of the proteins within the silk’s amorphous region, which influenced silk extensibility and toughness. Variations in structural alignment in the crystalline and non-crystalline regions influenced ultimate strength independent of genetic expression. Our study provides the deepest insights thus far into the mechanisms of how MA silk properties vary from gene expression to nanostructure formations to fiber mechanics. Such knowledge is imperative for promoting the production of synthetic silk fibers.蜘蛛不同尺度下的大壶状腺丝（major ampullate silk，MA丝）性能变异情况始终难以探明，这也成为复刻MA丝性能的合成纤维研发过程中的一大阻碍。目前已有多种技术可用于表征丝纤维性能的多尺度特征。本研究为5种园蛛总科（Araneoidea）蜘蛛喂食含蛋白或无蛋白的溶液，并开展了丝纤维拉伸力学测试、小角与广角X射线散射（small and wide-angle X-ray scattering，SAXS/WAXS）、氨基酸组成分析以及丝蛋白基因表达分析，以期解答长期存在的科学问题：营养匮乏如何跨尺度诱导MA丝力学性能的变异。分析结果显示，不同蜘蛛的丝纤维性能对蛋白质摄入变化的响应模式各不相同。我们发现，晶体与非晶体纳米结构的变化在本次研究观测到的性能变异中发挥了特定调控作用。在所有实验处理组中，5个物种的大壶状腺丝蛋白（major ampullate spidroin，MaSp）表达模式均存在差异。我们发现，在多数物种中，MaSp表达与氨基酸组成的变异并不符合基于传统MaSp表达模型所做出的预测。总体而言，丝纤维中丙氨酸与脯氨酸组成的变化会影响丝纤维非晶区域内蛋白质的排列方式，进而影响丝纤维的延展性与韧性。晶体与非晶体区域的结构排列变异则会独立于基因表达，对丝纤维的极限强度产生影响。本研究迄今为止最为深入地阐明了MA丝性能从基因表达、纳米结构形成到纤维力学性能的变异机制。该研究成果对于推动合成丝纤维的量产具有重要意义。