Silkworms transformed with chimeric silkworm/spider silk genes spin composite silk fibers with improved mechanical properties

Abstract

The development of a spider silk-manufacturing process is of great interest. However, there are serious problems with natural manufacturing through spider farming, and standard recombinant protein production platforms have provided limited progress due to their inability to assemble spider silk proteins into fibers. Thus, we used piggyBac vectors to create transgenic silkworms encoding chimeric silkworm/spider silk proteins. The silk fibers produced by these animals were composite materials that included chimeric silkworm/spider silk proteins integrated in an extremely stable manner. Furthermore, these composite fibers were, on average, tougher than the parental silkworm silk fibers and as tough as native dragline spider silk fibers. These results demonstrate that silkworms can be engineered to manufacture composite silk fibers containing stably integrated spider silk protein sequences, which significantly improve the overall mechanical properties of the parental silkworm silk fibers.biomaterials | biotechnology | transgenic animals

The Nephila clavipes genome highlights the diversity of spider silk genes and their complex expression

“…Systematic characterization of the diversity, number, and structure of the repetitive elements found in N. clavipes spidroins yields the key observations that 66% of repeated motif variants are shared both within and across spidroin classes, whereas 95% of cassette variants are private to individual spidroins. Together, these observations suggest that the assembly of shared motifs into distinct cassettes, often organized into larger repeat ensembles 29 , may underlie the range of unique biophysical characteristics observed for the various spider silk classes-an idea also supported by recent results from transgenic spidroin expression in silkworm 33,67 . Given the relationships already observed between spidroin motif sequences and structural properties of silk proteins 34 , the extensive catalog of novel motifs and combinations reported here provides many candidates for transgenic studies.…”

With great structure comes great functionality: Understanding and emulating spider silk

“…109 The early results in this area are encouraging: hybrid recombinant silks incorporating spider silk sequences produced by B. mori could be expressed with reasonable yields. 81 Fibers were found to be as tough as dragline spider silk, but exhibited a strength intermediate between B. mori and dragline spider silk. 81 B. mori, as a silk spinning insect, is therefore an ideal test bed to optimize sequences for commercial applications and to delineate the roles of protein sequence and processing in the properties of synthetic fibers to allow quantitative comparisons between research groups.…”

“…81 Fibers were found to be as tough as dragline spider silk, but exhibited a strength intermediate between B. mori and dragline spider silk. 81 B. mori, as a silk spinning insect, is therefore an ideal test bed to optimize sequences for commercial applications and to delineate the roles of protein sequence and processing in the properties of synthetic fibers to allow quantitative comparisons between research groups. The very different flow characteristics of spider and silkworm silk production, 110 however, suggest that this approach may be limited with respect to creating fully biomimetic spider silks.…”

“…52 While these methods have been reported for silk production, the resulting materials have not replicated the properties of natural spider silks. Beyond mammalian expression, the use of transgenic silk worms 81,95 is particularly interesting and would enable direct spinning of high molecular weight fibers (see below).…”

“…Heterologous silk protein studies have been conducted using a range of organisms including bacteria, 78 tobacco plants, 79 yeast, 80 silkworms, 81 goats, 82 and mammalian cells 83 (for an in-depth review, see Refs. 9 and 52).…”