Multiscale mechanisms of nutritionally induced property variation in spider silks

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.

The common house spider,Parasteatoda tepidariorum, maintains silk gene expression on sub-optimal diet

“…Another functional difference between cobwebs and orb-webs is that cobwebs incorporate major ampullate silk as structural support for the entire three-dimensional webs, whereas orb-webs use major ampullate silk to absorb the impact of flying prey [23]. Thus, it is possible the major ampullate silk of orb-web weavers has greater inherent variability to adjust the web functionality, which may be triggered by changes in nutrient uptake [23,26]. It was found under nutrient deprivation, the major ampullate silk of a cobweb species, Latrodectus hasselti, was unaffected in terms of material properties (Blamires et al, 2018).…”

Spider silk colour covaries with thermal properties but not protein structure

“…The solution used for the protein-fed treatment was identical to that described by Blamires et al [41,49]: a mixture of 10 g of a 10% albumin solution with 6 g of sucrose in 60 ml of water. The solution for the protein-deprived treatment was 8 g of sucrose in 30 ml of water.…”

“…Third, the β-sheet secondary structures and crystalline tertiary structures of MA silk are anisotropic, thus highly birefringent [39,40]. Given that the size, density and alignment of β-sheets can vary across spider species [41], this may contribute to variation in MA silk optical properties across species. Fourth and finally, the thermal properties of MA silk, particularly the silk's enthalpy (a measure of the total internal energy in the silk thread), glass transition temperature (T g ) and melt temperature, are hypothesized to covary with the size and alignment of the silk's crystalline structures and, thus, correlate with its birefringent properties [42,43].…”

Spider Silk Biomimetics Programs to Inform the Development of New Wearable Technologies

“…They thus provide a basis for bioprospecting for extremely high performing silks for biomimetics programs (Agnarsson et al, 2010), and might be used to pinpoint the most flexible mechanical properties of a particular silk to show us how to better control property variability . Nonetheless, few studies have documented all of the relevant property variations across macroto nano scales (but see Blamires et al, 2018;Lacava et al, 2018). A deeper exploration of this largely untapped research space will enable the development of biomimetic protocols with more precise control of property variability.…”

“…The suppression of key nutrients and/or metabolic rates in spiders under dietary stress leads to a compromised investment in key amino acids and other building blocks of the silk proteins (Craig et al, 2000;Guehrs et al, 2008;Blamires et al, 2012a), leading to a compromise in properties (Zax et al, 2004;Blamires et al, 2015aBlamires et al, , 2018. It thus seems like the investment costs are most prominent and identifiable when the spider is under dietary stress .…”