Abstract
Albeit silks are fairly well understood on a molecular level, their hierarchical organisation and the full complexity of constituents in the spun fibre remain poorly defined. Here we link morphological defined structural elements in dragline silk of Nephila clavipes to their biochemical composition and physicochemical properties. Five layers of different make-ups could be distinguished. Of these only the two core layers contained the known silk proteins, but all can vitally contribute to the mechanical performance or properties of the silk fibre. Understanding the composite nature of silk and its supra-molecular organisation will open avenues in the production of high performance fibres based on artificially spun silk material.
Highlights
Spider silks display extraordinary mechanical features [1] and the toughness of some dragline or major ampullate silks even rival man-made high-tech fibres [2]
Whereas the dragline fibre of Nephila clavipes looked unstructured in transmission electron microscopy (TEM), the dragline of N. edulis showed the existence of a multilayer assembly [10,11,32]
Grooves that became evident on the surface of the fibre after treatment with hexafluorisopropanol might match an interwoven fibrillar network reported for the skin (Figure 5C) [31]
Summary
Spider silks display extraordinary mechanical features [1] and the toughness of some dragline or major ampullate silks even rival man-made high-tech fibres [2]. The properties of dragline silk are believed to depend on both the molecular design of its two main protein components termed major ampullate spidroins 1 (MaSp1) and 2 (MaSp2) and the hierarchical organisation of structural elements [9,10,11,12] Both major ampullate spidroins are rich in glycine and alanine residues which form short GGX, GA and GPGXX (X, subset of amino acids) as well as poly-A motifs [6]. The amide to amide interactions of the protein backbones in the bsheets are thought to give a strong molecular cohesion and confer strength to the fibre These crystalline areas are embedded in an amorphous matrix that is formed by the glycine enriched motifs (GGX in MaSp 1, GPGXX in MaSp 2), which adopt 31helical and type II b-turn structures [15]. These amorphous regions are believed to confer elasticity to the fibre [3,15]
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