Conformational Transitions and Self-assembly of Regenerated Spider Silk Protein in Water

Spider silk, relying on its exceptional mechanical properties, has attracted extensive attention throughout the world. The structure of a material can influence its mechanical properties. Investigation of the structure of spider silk includes amino acid composition, molecular structure, self-assembly, and crystallization, among other characteristics. Herein, the effects of concentration, time, alkali metal ions （Na^＋and K ^＋ ） and pH on the conformational transition and self-assembly of regenerated Ornithoctonus huwena spider dragline silk protein （spidroin） in water were investigated using circular dichroism （CD） and atomic force microScopy （AFM）. Spidroin concentration, time and Na ＋ ions slightly influenced the conformational transition of spidroin molecules. However, K ＋ ions and pH induced the formation of a β- sheet structure. Increasing spidroin concentration or time increased the aggregation of spidroin and enhanced the formation of nanoffiaments. K ~ ions enhanced the serf-assembly of spidroin into nanofilaments. The self-assembled nanofilaments appeared at a pH of approximately 6. 11. Both lower and higher pH induced aggregation. At a lower pH, the aggregation was composed of nanopartides, whereas higher pH induced the aggregation of nanoffiaments, likely from the synergistic effect of Na ^＋ ions and pH.