Spider silk spidroins

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.)...

Yeast and bacterial systems often give low levels of expression of silks, and this has led to the development of production systems in tobacco and potato. Scheller et al. (2001) have shown that spider silk proteins can be produced in transgenic plants. They inserted synthetic spider silk protein (spidroin) genes into transgenic plants under the control of the CaMV35S promoter. Using this system they were able to demonstrate the accumulation of recombinant silk proteins to a level of at least 2% of total soluble protein in the endoplasmic reticulum of tobacco leaves, and potato tubers. 

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). 

C- and N-terminal regions of spidroin are highly conserved among the spider silk proteins and play an important role in the assembly of spidroin (Huemmerich et al., 2004 Motriuk-Smith et al., 2005). 

Although the amino acid sequence as well as the secondary structure of fibroin differs from those of spidroin, the fibers spun from these proteins, that is, silkworm silk and spider silk have comparable mechanical properties. These may be attributed to the structural characteristics, both at the molecular and filament level. The superior mechanical properties of silk-based materials, such as films, coatings, scaffolds, and fibers produced using reconstituted or recombinant silk proteins, are determined by their condensed structures. 

The wet spinning of regenerated spidroin was reported in the early 1990s by Jelinski et al. They dissolved spider silk in hexafluoroisopro-panol (HFIP) at a concentration of 2.5 wt% to produce an artificial fiber using water, methanol, isopropanol, and acetone as coagulation bath. The reconstituted silk could only be shaped in acetone but the structure... 

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... 

Spidroins as ablu rint for recombinant spider silk proteins... 

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).

---