Spidroin recombinant

Table 4 Examples of wet spinning processes using regenerated fibroin, spidroin, and recombinant spidroin, with different solvents and coagulation baths (Zhou et al., 2006a)...

As mentioned above, expression of recombinant spidroins has often resulted in water insoluble products. Often the purification processes in these cases are obligated to include solubilisation steps using urea, guanidine hydrochloride, lithium bromide. 

If the intended use of the recombinant spidroin involves biomedical applications, the scaffolds should be sterilized before usage. This has been achieved by using filtration, ethanol, ethylene oxide or by autoclaving (Table 1). In some cases, the scaffolds have been pre-incubated in cell culture medium before cell culture. Whether traces of the agents used during production still remain in the scaffolds has not been investigated. However, the processes seem to result in scaffolds suitable for cell culture (see further below). 

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. 

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. 

Figure 7 The morphologies of regenerated spidroin silks, (a) The silk formed in acetone and subsequently stretched (Seidel et al, 2000). (b) Silk drawn out of solution into air (Shao et al, 2003). (c) Silk produced from the recombinant ADF-3 (Lazaris et al, 2002).

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

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. 

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).

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