Fibers from Recombinant Proteins

Natural protein fibers such as spider silks have extraordinary properties, but it is difficult and impractical to obtain quantities of spider silk required for applications through the natural spinning process. To overcome this limitation, extensive efforts have been made to produce regenerated spider silk proteins using biotechnological approaches. Several heterologous host systems such as bacteria, yeast, mammalian cells, and transgenic plants, animals, and insects have been used to produce spider silk proteins as seen in Table 50.1 [12Chu]. Tokareva et al. provide a thorough review of the approaches used to produce recombinant spider silks and the limitations of the approaches [13Tok]. One of the most common and easiest approaches to obtain artificial spider silk is through bacterial production [07Ven]. Several researchers have expressed spider silk genes in Escherichia coli and have studied the structure, properties, and functions of protein fibers. Although bacterial production of proteins is possible on an industrial scale, several limitations have been expressed for this approach. The size of the expressible gene in E. coli is considerably smaller than the native gene found in spiders, and the bacteria use a distinct codon different than that in spiders. In addition, bacteria often remove repetitive sequences that are necessary to obtain the properties seen in spider silk fibers. To overcome these limitations, engineered genes that include the bacterial codon have been developed and expressed in E. coli. In one approach, artificial genes that encode the analogs of the proteins (spidroins 1 and 2) found in Nephila clavipes dragline silk were expressed in E. coli [97Fah1]. Proteins with purity of up to 99 % were obtained, and both the spidroins had mostly random structures.