Spider dragline silk fibres maintain rectangular columnar liquid crystalline phase

The liquid crystalline phase of spider silk is thought to enable for the silk protein to be stored at high concentration in the gland without gelation, facilitating the instant fibre formation at the spinning duct. Nevertheless, it has never been revealed whether the liquid crystalline state of the silk protein maintains after the fibre formation. In this study, we conducted the X-ray liquid crystal structure analysis to reveal the details of molecular assemblies of the native spider silk proteins. Based on the wide- and small angle X-ray scattering data using the uniaxial bundle of spider draglines, the spider dragline silk fibres maintain a rectangular columnar liquid crystalline phase with a P2(1)/a (p2gg) symmetry. The liquid crystalline state of the spider silk fibre is not nematic, cholesteric, nor hexagonal columnar, as previously proposed, but rectangularly packed columnar liquid crystal. The movable silk molecular chains along the long fibre axis in the rectangular columnar liquid crystalline structure help to explain the mechanical strength of the native spider dragline silk fibres. The results obtained in this study will contribute to understanding the biological basis underlying the silk fibre formation and will be useful to the biomimicry of spider silk fibres.

Automated summary

The liquid crystalline phase of spider silk allows for high concentration storage of the silk protein in the gland, facilitating instant fibre formation. Through X-ray liquid crystal structure analysis, it has been revealed that spider dragline silk fibres maintain a rectangular columnar liquid crystalline phase. This unique structure explains the mechanical strength of the native spider dragline silk fibres. The findings of this study have important implications for understanding silk fibre formation and biomimicry of spider silk fibres.