Abstract
Variability in spider major ampullate (MA) silk properties at different scales has proven difficult to determine and remains an obstacle to the development of synthetic fibers mimicking MA silk performance. A multitude of techniques may be used to measure multiscale aspects of silk properties. Here we fed five species of Araneoid spider solutions that either contained protein or were protein deprived and performed silk tensile tests, small and wide-angle X-ray scattering (SAXS/WAXS), amino acid composition analyses, and silk gene expression analyses, to resolve persistent questions about how nutrient deprivation induces variations in MA silk mechanical properties across scales. Our analyses found that the properties of each spider’s silk varied differently in response to variations in their protein intake. We found changes in the crystalline and non-crystalline nanostructures to play specific roles in inducing the property variations we found. Across treatment MaSp expression patterns differed in each of the five species. We found that in most species MaSp expression and amino acid composition variations did not conform with our predictions based on a traditional MaSp expression model. In general, changes to the silk’s alanine and proline compositions influenced the alignment of the proteins within the silk’s amorphous region, which influenced silk extensibility and toughness. Variations in structural alignment in the crystalline and non-crystalline regions influenced ultimate strength independent of genetic expression. Our study provides the deepest insights thus far into the mechanisms of how MA silk properties vary from gene expression to nanostructure formations to fiber mechanics. Such knowledge is imperative for promoting the production of synthetic silk fibers.
Highlights
Spider major ampullate (MA) silk is nature’s toughest materials [1]
The MaSp1: MaSp2 expression patterns we found across treatments generally did not correspond with the amino acid compositions according to our expectations under a traditional MaSp expression model
While the above caveats may tempt us to think that the RT-PCR analyses yielded largely uncertain results, we found that the expression patterns for P. graeffei aligned exceptionally close to our expectation should the spiders be regulating MaSp1 and MaSp2 expression alone
Summary
Spider major ampullate (MA) silk is nature’s toughest materials [1]. There is considerable interest in the creation of materials that mimic its performance [2]. Attempts to recombine, amplify and spin spider silk proteins have not produced fibers with properties resembling those of naturally spun silk [3,4]. One reason for the inability to produce. Multiscale mechanisms of spider silk property variation
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