Variation in Protein Intake Induces Variation in Spider Silk Expression

Abstract

BackgroundIt is energetically expensive to synthesize certain amino acids. The proteins (spidroins) of spider major ampullate (MA) silk, MaSp1 and MaSp2, differ in amino acid composition. Glutamine and proline are prevalent in MaSp2 and are expensive to synthesize. Since most orb web spiders express high proline silk they might preferentially attain the amino acids needed for silk from food and shift toward expressing more MaSp1 in their MA silk when starved.Methodology/Principal FindingsWe fed three spiders; Argiope aetherea, Cyrtophora moluccensis and Leucauge blanda, high protein, low protein or no protein solutions. A. aetherea and L. blanda MA silks are high in proline, while C. moluccesnsis MA silks are low in proline. After 10 days of feeding we determined the amino acid compositions and mechanical properties of each species' MA silk and compared them between species and treatments with pre-treatment samples, accounting for ancestry. We found that the proline and glutamine of A. aetherea and L. blanda silks were affected by protein intake; significantly decreasing under the low and no protein intake treatments. Glutmaine composition in C. moluccensis silk was likewise affected by protein intake. However, the composition of proline in their MA silk was not significantly affected by protein intake.ConclusionsOur results suggest that protein limitation induces a shift toward different silk proteins with lower glutamine and/or proline content. Contradictions to the MaSp model lie in the findings that C. moluccensis MA silks did not experience a significant reduction in proline and A. aetherea did not experience a significant reduction in serine on low/no protein. The mechanical properties of the silks could not be explained by a MaSp1 expressional shift. Factors other than MaSp expression, such as the expression of spidroin-like orthologues, may impact on silk amino acid composition and spinning and glandular processes may impact mechanics.

Nanostructural and mechanical property changes to spider silk as a consequence of insecticide exposure

“…We note that similar shifts in spidroin expressions and MAS properties have been shown for spiders under nutritional stress (Blamires et al, 2012(Blamires et al, , 2015. Furthermore, there is speculation that these expression shifts occur because MaSp2 is metabolically more costly to synthesize than MaSp1 so is downregulated by spiders when under metabolic stress Blamires et al, 2012).…”

“…We note that similar shifts in spidroin expressions and MAS properties have been shown for spiders under nutritional stress (Blamires et al, 2012(Blamires et al, , 2015. Furthermore, there is speculation that these expression shifts occur because MaSp2 is metabolically more costly to synthesize than MaSp1 so is downregulated by spiders when under metabolic stress Blamires et al, 2012). Insecticides such as thiamethoxan and lambda-cyhalothrin disrupt nicotinic acetylcholine receptor proteins to inhibit neural propagation in invertebrates (Tomizawa et al, 1995;Jones and Sattelle, 2010).…”

“…5). Such compositional differences across treatments are suggestive of differential expressions of the two MAS proteins (spidroins), MaSp1 and MaSp2 (Xu and Lewis, 1990;Hinman and Lewis, 1992;Craig et al, 1999;Blamires et al, 2012). Explicitly, the silks of the control spiders appeared to contain more MaSp2 (identified by their greater proline and glutamine composition), while the insecticide exposed spider's silk appeared to contain more MaSp1.…”

Do habitat features affect the composition of silk proteins by Namibian arid-adaptedAriadnaspiders (Araneae: Segestriidae)?

“…However, the FT-IR analysis does not give complete information on the composition of the silks studied. Taking into account the FT-IR and MALDI-MS data and the published studies on the chemical characterization of spider silks (Craig et al 2000;Papadopoulos et al 2007;Vasanthavada et al 2007;Kluge et al 2008;Romer & Scheibel 2008;Blamires et al 2012), we suggest that mass difference of 198 Da corresponds to the proline-threonine (P-T) peptide sequences; that of 199 Da corresponds to the alanine-alanine-glycine (A-A-G) amino acids sequences; that of 215 Da corresponds glycine-alanine-serine (G-A-S) repeats; that of 225 Da corresponds to the glycine-alanine-proline (G-A-P) repeats; that of 231 Da is due to the serine-serineglycine (S-S-G) triad sequence; that of 245 Da belongs to the serine-serine-alanine (S-S-A) repeats. The mass differences of the most common amino acid sequences are summarized in Table III.…”

Life history trade-offs imposed by dragline use in two money spiders

“…Based on conservative assumptions (Prestwich, 1977), 18% of all costs are related to spinning activity, the remainder to physiological silk production costs. Variation in protein (Blamires et al, 2012a) and carbohydrate (Blamires et al, 2015) intake determines the amino acid composition of silk and the architectural plasticity of the produced webs. Both silk production and silk spinning are therefore highly dependent on nutritional intake.…”