Quantitative Correlation between Primary Sequences and Conformations in 13C-Labeled Samia cynthia ricini Silk Fibroin during Strain-Induced Conformational Transition by 13C Solid State NMR

Stretching-Induced Conformational Transition of [3-13C]Ser- and [3-13C]Tyr-Antheraea yamamai Silk Fibroin before Spinning Investigated with 13C Solid-State NMR Spectroscopy

The conformational transition of [3-¹³C]Ser- and [3-¹³C]Tyr-Antheraea yamamai silk fibroin before spinning induced by stretching was investigated with ¹³C CP/MAS NMR spectroscopy. The α-helix content of the silk fibroin before stretching was found to be 31.6% based on the Ala and Ser peaks. With increasing stretching ratio, the α-helix and the random coil Ala Cβ peaks decreased gradually, while the β-sheet peak was observed at a stretching ratio of ×5 and increased rapidly upon further stretching. For Ser residue, the α-helix peak decreased monotonically with increasing stretching ratio, but the random coil peak increased slightly till the stretching ratio of ×5 and then decreased. A small β-sheet peak was observed before stretching and then increased rapidly starting from the stretching ratio of ×7. In contrast, a gradual decrease of random coil peak and an increase of β-sheet peak were observed for the Tyr residue. The results of this investigation may be helpful for further studies of fiber formation mechanism in A. yamamai and in the future design of artificial silk materials.

Structural Comparison of Various Silkworm Silks: An Insight into the Structure-Property Relationship

Silkworm silk has attracted considerable attention in recent years due to its excellent mechanical properties, biocompatibility, and promising applications in biomedical sector. However, a clear understanding of the molecular structure and the relationship between the excellent mechanical properties and the silk protein sequences are still lacking. This study carries out a thorough comparative structural analysis of silk fibers of four silkworm species ( Bombyx mori, Antheraea pernyi, Samia cynthia ricini, and Antheraea assamensis). A combination of characterization techniques including scanning electron microscopy, mechanical test, synchrotron X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), and NMR spectroscopy was applied to investigate the morphologies, mechanical properties, amino acid compositions, nanoscale organizations, and molecular structures of various silkworm silks. Furthermore, the structure-property relationship is discussed by correlating the molecular structural features of silks with their mechanical properties. The results show that a high content of β-sheet structures and a high crystallinity would result in a high Young's modulus for silkworm silk fibers. Additionally, a low content of β-sheet structures would result in a high extensibility.