The mechanical design of spider silks: from fibroin sequence to mechanical function

ABSTRACT Spiders produce a variety of silks, and the cloning of genes for silk fibroins reveals a clear link between protein sequence and structure–property relationships. The fibroins produced in the spider’s major ampullate (MA) gland, which forms the dragline and web frame, contain multiple repeats of motifs that include an 8–10 residue long poly-alanine block and a 24–35 residue long glycine-rich block. When fibroins are spun into fibres, the poly-alanine blocks form β-sheet crystals that crosslink the fibroins into a polymer network with great stiffness, strength and toughness. As illustrated by a comparison of MA silks from Araneus diadematus and Nephila clavipes, variation in fibroin sequence and properties between spider species provides the opportunity to investigate the design of these remarkable biomaterials.