Mechanism of silk processing in insects and spiders

초록

Silk spinning by insects and spiders leads to the formation of novel fibers that exhibit high strength and toughness. The lack of understanding of the protein processing in silk glands has prevented the recapitulation of these properties in vitro from reconstituted or genetically engineered silks. In the present study, we identified emulsion formation and micellar structures from aqueous solutions of reconstituted silkworm silk fibroin as a first step in the process. The 100 to 200 nm diameter sizes of these structures could be predicted from hydrophobicity plots of silk protein primary sequence. These micelles subsequently aggregated into larger ‘globules’ and gel-like states as the concentration of silk fibroin increased, while maintaining solubility due to the hydrophilic regions of the protein interspersed among the larger hydrophobic regions. Upon physical shearing or stretching structural transitions, increased birefringence and morphological alignment were demonstrated, indicating that this process mimics the behavior of native silk proteins in vivo. Final morphological features of there silk materials are strikingly similar to those observed in native silkworm fibers.