Spider silk, fiber formation

It is now clear from the study of silk fiber formation in lepidoptera and spiders (Akai, 1998 Iizuka, 1966 Kerkam et aL, 1991 Knight and... 

Work, R. W. (1977). Mechanisms of major am-pullate silk fiber formation by orb-web-spinning spiders. Trans. Am. Mictvse. Soc. 96,170-189. 

Fig. 3. Solubility of silk proteins in solution as a function of time. Low solubility corresponds to protein aggregation. The fast and slow aggregations are observed in vitro (Dicko et al., 2004a), whereas the stable helical conformation (storage structure) is observed in vivo (Dicko et al., 2004b,d). This illustrates the inherent instability of silk protein in solution and shows the /(-sheet polymorph structure as the most stable form. In other words, the spiders actively control and modulate the unavoidable silk protein aggregation prior to fiber formation.

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. 

Silk is a protein fiber spun by silkworm, which is the caterpillar or larva of the domesticated silkmoth, Bombyx mori. In addition to silkworm, many other insects or non-insects (eg., spider) can spin silk fibers. However, the silk of Bombyx mori is the mainstay of commercial silk production and consumption. This section will only discuss the formation of silk fiber by silkworm. 

With the exception of silk, which the silkworm or spider extrudes as a continuous filament, natural fibers are of finite length. For textile use, these need to be cleaned and then spun into threads or yams. Synthetic fibers, on the other hand, are continuous filaments produced from a solution or melt. The term spinning is used to describe the formation of synthetic fibers, but in this sense it has no relation to the process for combining fibers into threads. 

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). 

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