Mechanism of silk processing in insects and spiders

• Published in: Nature Vol. 424; no. 6952; pp. 1057 - 1061
• Main Authors: Kaplan, David L, Jin, Hyoung-Joon
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 28-08-2003; Nature Publishing Group
• Subjects: Animals; Arachnida; Biochemistry. Physiology. Immunology; Biological and medical sciences; Biology; Emulsions - chemistry; Emulsions - metabolism; Fibers; Fundamental and applied biological sciences. Psychology; Hydrophobic and Hydrophilic Interactions; Insect Proteins - chemistry; Insect Proteins - metabolism; Insect Proteins - ultrastructure; Insecta; Insecta - chemistry; Insecta - metabolism; Insects; Invertebrates; Micelles; Physiology. Development; Protein Binding; Protein Folding; Protein Structure, Secondary; Silk; Solutions - chemistry; Solutions - metabolism; Spiders; Spiders - chemistry; Spiders - metabolism; Scanning electron microscopy; Molecular structure; Insecta; Micelle; Araneida; Biosynthesis; Bombyx mori; Hydrophobicity; Protein; Nephila clavipes; Arachnida; Silk; Emulsion; Ultrastructure; Arthropoda; Bombycidae; Lepidoptera; Fibroin; Invertebrata; Formation; Araneidae
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature01809

Silk spinning by insects and spiders leads to the formation of fibres 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. Here we report the identification of emulsion formation and micellar structures from aqueous solutions of reconstituted silkworm silk fibroin as a first step in the process to control water and protein-protein interactions. The sizes (100-200 nm diameter) 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 owing 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 behaviour of similar native silk proteins in vivo. Final morphological features of these silk materials are similar to those observed in native silkworm fibres.