Spidroin 1 and

Spider silk only has one protein monofilament, and the core-skin structure has been observed in some of them (Frische et al., 1998 Poza et al., 2002). It is thought that both the skin and the core are mainly composed of spidroins, which are differed from the primary structure (spidroin 1 and spidroin 2, >350 kDa calculated from mRNA) (Hinman and Lewis, 1992 Sponner et al., 2005a, b Xu and Lewis, 1990). 

Biologically produced dragline silk is a combination of two liquid proteins, Spidroin 1 and 2, which become oriented and solidify as they travel through a complex... 

The poly-alanine stretches in spidroin 2 are somewhat longer than those of spidroin 1 and therefore would be more suitable for the formation of P-sheets. However, the proline residues in the glycine rich neighbourhood are rather detrimental to a formation of P-pleated sheets and would disrupt the integrity of the conformation. It was proposed that spidroin 2 should therefore be exclusively found in the amorphous matrix while solely motifs found in spidroin 1 are responsible for the formation of non-periodic lattices (NPL) in the crystalline fraction [57,58]. Yet, attempts to investigate the conformation of spidroin 2 with NMR failed as no labelled proline could be found [66]. Thus the role of spidroin 2 in the molecular structure remains speculative. 

Hedhammar, M., Rising, A., Grip, S., Martinez, A.S., Nordting, K., Casals, C., Stark, M., Johansson, J., 2008. Stmctural properties of recombinant nontepetitive and repetitive parts of major ampuUate spidroin 1 from Euprosthenops australis imphcations for fiber formation. Biochentistry 47 (11), 3407—3417. 

Solid-state NMR study of structural heterogeneity in peptides containing both polyalanine and repeated GGA sequences as a local structural model of Nephila clavipes dragline silk (Spidroin 1) has been reported. Solvent treatments prior to the NMR measurements were shown to induce a structural change in these model peptides. Conformation-dependent NMR chemical shifts were used to determine the local structure, including the evaluation of the fraction of several conformations. 

Fig. 11.1 Synthetic spidroin and spidroin-ELP plant expression cassettes.

Silk proteins (spidroins in spiders and fibroins in Lepidoptera insects) are assembled into well-defined nanofibrillar architectures (Craig and Riekel, 2002 Eby et al., 1999 Inoue et al., 2000b, 2001 Li et al., 1994 Putthanarat et al, 2000 Vollrath et al., 1996). Spidroins and fibroins are largely constructed from two chemically distinct repetitive motifs or blocks (Table I), an insoluble crystalline block and a soluble less-crystalline block (Craig, 2003 Fedic et al., 2002 Hayashi and Lewis, 2000 Hayashi et al., 1999). The crystalline blocks are composed of short side-chained amino acids in highly repetitive sequences that give rise to /1-sheet structures. 

Fig. 4. Time-induced conformational change of spider silk protein (spidroin) in solution. Solutions of silk proteins at 1% w/v in distilled water were monitored using circular dichroism. The graph shows a change in secondary structure with time. The silk proteins underwent a kinetically driven transition from a partially unfolded structure to a -sheet-rich structure (from Dicko et al., 2004c). ( ) after 0 days, (O) after 1 day, and (A) after 2 days. The conformational change appeared faster at 20°C compared to 5°C, suggesting a hydrophobically driven mechanism. (Copyright 2004 American Chemical Society.)...

Table 1 The structure elements in fibroin and spidroin (Hakimi et al, 2007).

Peng, X.N., Shao, Z.Z., Chen, X., Knight, D.P., Wu, P.Y., and Vollrath, F. "Further investigation on potassium-induced conformation transition of Nephila spidroin film with two-dimensional infrared correlation spectroscopy". Biomacromolecules 6(1), 302-308... 

Figure 1. Scaffolds of recombinant spider silk. Upper row photograph of a wet fiber (left) and scanning electron micrograph of a dried fiber (right). Lower row photograph of a wetfoam (left) and scanning electron micrograph of a dried foam (right). All scaffolds were made from the miniature spidroin 4RepCT (see Table 1).

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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