Spider silks

Spider silks are a little different and much more extensible. They are made up of two proteins, spidroin I and spidroin II, which vary somewhat with species and diet. Like silkworm silk, these proteins contain high proportions of glycine and alanine (about 42% and 25%, respectively), but differ in the proportions of the other, more bulky amino acids present In addition, these proteins-have 4—9 alanine residues strung together in a block, which, in turn, are linked by glycine 

FIGURE 9-19 The rippled or pleated structure of Bombyx mori silk. 

The major advantage of enzymatic processes is the possibility of using conventional technology already existing in textile plants. Enzyme formulations should be applied in solution, to avoid dust formation and to reduce the known allergizing potential of protein material when inhaled. A heat treatment is sufficient to stop the enzymatic action irreversibly. Thus the transfer of an enzymatic process developed on laboratory scale into the textile industry should be possible without great delay. 

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Spider Silk. Spider silks function ki prey capture, reproduction, and as vibration receptors, safety lines, and dispersion tools. Spider silks are synthesized ki glands located ki the abdomen and spun through a series of orifices (spinnerets). The types and nature of the various silks are diverse and depend on the type of spider (2). Some general categories of silks and the glands responsible for thek production are Hsted in Table 1. 

Table 1. Function and Location of Spider Silk Glands ...

Crystallinity. Generally, spider dragline and silkworm cocoon silks are considered semicrystalline materials having amorphous flexible chains reinforced by strong stiff crystals (3). The orb web fibers are composite materials (qv) in the sense that they are composed of crystalline regions immersed in less crystalline regions, which have estimates of 30—50% crystallinity (3,16). Eadier studies by x-ray diffraction analysis indicated 62—65% crystallinity in cocoon silk fibroin from the silkworm, 50—63% in wild-type silkworm cocoons, and lesser amounts in spider silk (17). 

Spider silk is nature s high-performance fiber... 

Bram, A., et al. X-ray diffraction from single spider silk fibers. J. Appl. Cryst. 30 390-394, 1997. 

FIGURE 9.29 Analysis of natural spider silk (spider web). Columns PSS PFG 100 + 1000. Eluent HFIP + 0.1 M KtFat. Temp 2S°C. Detection UV 2S4 nm, Rl. Calibration PSS PMMA ReadyCal kit. 

This combination of strength and flexibility derives from the eomposite nature of spider silk. As keratin protein is extruded from... 

The complexity and versatility of materials made by nature are the envy of scientists. We are only beginning to be able to create materials that have the strong yet porous structure of bone or the strength and flexibility of spider silk (Section 19.13). However, some materials are not strong they are soft and flexible. These materials, some of which are described in the following two sections, are also important to industry and medicine and some are vital to life. 

The structures of some natural protein-based materials, such as silk and wool, result in strong, tough fibers. Spiders and silkworms use proteins as a structural material of remarkable strength (Fig. 19.22). Chemists are duplicating nature by making artificial spider silk (Fig. 19.23), which is one of the strongest fibers known. 

FIGURE 19.23 Artificial spider silk can now be made in bulk. It can be spun into thin, tough thread, like that on the spools shown here, or wound into cables strong enough to support suspension bridges. 

Hayashi C. and Lewis R., Molecular architecture and evolution of a modular spider silk protein gene. Science, 287, 1477, 2000. 

Hayash C.I., Shipley N., and Lewis R., Hypotheses that correlate the sequence, structure, and mechanical properties of spider silk proteins, Int. J. Biol. Macromol., 24, 271, 1999. 

Lazaris, A., Arcidiacono, S., Huang, Y., Zhou, J.F., Duguay, F., Chretien, N., Welsh, E.A., Soares, J.W., and Karatzas, C.N., Spider silk fibers spun from soluble recombinant silk produced in mammalian cells. Science, 295(5554), 472- 76, 2002. 

Parkhe AD, Seeley SK, Gardner K (1997) Structural studies of spider silk proteins in the fiber. J Mol Recognit 10 1-6... 

Slotta U, Hess S, Spiess K et al (2007) Spider silk and amyloid fibrils a structural comparison. Macromol Biosci 7 183-188... 

Examples. 2D SAXS/WAXS experiments on highly anisotropic polymer materials during melting and crystallization can be used to visualize and understand the evolution of nanostructure [56,57], Transformations of biopolymers in solution, e.g., virus crystallization can be studied in situ [58], It is possible to study solidification mechanisms of spider silk [59], or the self-assembly of micelles on a time-scale of milliseconds [60],... 

Production of Spider Silk Proteins in Transgenic Tobacco and Potato... 

Tab.11.1 Spider silk proteins MaSpI, MaSpll and Flag from Nephila davipes.

Strategies for the Production of Recombinant Spider Silk Proteins... 

I I Synthetic spider silk protein SOI I I ER retention signal (KDEL)... 

Synthetic Spider Silk Fibers Natural i/s Artificial Spinning Strategies... 

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. 

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