Spider silk Nephila clavipes

Raw silk was dissolved in hexafluoro-iso-propanol (HFIP) [17, 33]. A typical working concentration for spinning was 2.5% (w/v) silk fibroin in HFIP. The spinning solution was pressed through a small needle (0 80-250 pm) into a precipitation bath (methanol for Bombyx mori silk proteins and acetone for Nephila clavipes silk proteins) and the silk solution immediately precipitated as a fiber. The best performing fibers approached the maximum strength measured for native fibers of Bombyx mori, but did not achieve the mechanical properties of natural spider silk. 

Composition of the silk lipids of the spider Nephila clavipes. Lipids 36 637-647. 

Spider silk is composed of large polypeptides, 250-320 kDa. A 285 kDa protein from the spider Nephila clavipes was generated in E. coli and purified. Its structural properties were superior to smaller-molecular-weight proteins. The glycine-rich (44% of residues) protein was generated by increasing the pool of glycyl-tRNA [142]. 

Cunniff, P.M., Fossey, S.A.. Auerbach, M.A. and Song, J.W. (1994) Mechanical properties of major ampullate gland silk fibers extracted from Nephila clavipes spiders. In Silk Polymers Materials Science and Biotechnology, pp. 234-251, D. Kaplan, W.W. Adams, B. Farmer and C. Viney (Eds.). American Chemical Society. Washington, DC. 

Craig, C., Spider webs and silks, 2004, Oxford UK Oxford University Press. Augsten, K.,Weisshart, K., Sponner, A. and Unger, E., Glycoproteins and skin-core structure in Nephila clavipes spider silk observed by light- and electron microscopy. Scanning, 1999, 21(2) 77. 

Silks are generally defined as protein polymers that are spun into fibers by some lepidoptera larvae such as silkworms, spiders, scorpions, mites, and flies [331-333]. Silk proteins are usually produced within specialized glands after biosynthesis in epithelial cells, followed by secretion into the lumen of these glands where the proteins are stored before being spun into fibers. Silks differ widely in composition, structure, and properties, depending on the specific source. The most extensively characterized silks are from the domesticated silkworm, Bombyx mori, and from spiders Nephila clavipes and Araneus diademaius). Many of the more evolutionarily advanced spiders synthesize different types of silks. Each of these different silks has a different amino acid composition and exhibits mechanical properties tailored to their specific functions reproduction as cocoon capsular stmctures, lines for prey capture, lifeline support (dragline), web constmction, and adhesion [334]. 

Silk fibers formed by the secretion of the major ampullate glands of the spider Nephila clavipes also involve the linear supramolecular aggregation of a globular protein (fibroin). The formation of rodlike aggregates is consistent with the observation of a precursor liquid crystalline phase before fiber solidification [135,136]. Details of this supramolecular polymerization are still unclear. 

Chimeric (fusion) proteins that incorporate the R5 peptide have been synthesized to control and precipitate silica nanoparticles. Po Foo and coworkers have utilized a two-component chimeric protein consisting of the R5 polypeptide (from C. fusiformis) and the self-assembling domain based on the consensus repeat in the major ampullate spidroin protein 1 (MaSpl) of Nephila clavipes spider dragline silk [64]. MaSpl forms highly stable P-sheet secondary stmctures that can be spun into intricate fibers which, when fused with the sihca-templating R5-peptide, allow for the formation of film-like and fibrous silica structures (Figure 1.18). 

The potential use of spider silk as a new biomaterial has led to the evaluation of various heterologous expression systems for the production of recombinant spider silk-like proteins [65]. Partial cDNA constructs of dragline silk protein were cloned and expressed in Escherichia coli [66], mammalian cell lines (MAC-T/bovine and BHK (baby hamster kidney)/hamster) [67], insect-cell lines [68, 69], and transgenic silkworm larvae [69]. Designer synthetic genes based on Nephila clavipes spider dragline and fiagdliform protein sequences have also been expressed in E. coli... 

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