Identification and dynamics of polyglycine II nanocrystals in Argiope trifasciata flagelliform silk

Abstract

Spider silks combine a significant number of desirable characteristics in one material, including large tensile strength and strain at breaking, biocompatibility, and the possibility of tailoring their properties. Major ampullate gland silk (MAS) is the most studied silk and their properties are explained by a double lattice of hydrogen bonds and elastomeric protein chains linked to polyalanine β-nanocrystals. However, many basic details regarding the relationship between composition, microstructure and properties in silks are still lacking. Here we show that this relationship can be traced in flagelliform silk (Flag) spun by Argiope trifasciata spiders after identifying a phase consisting of polyglycine II nanocrystals. The presence of this phase is consistent with the dominant presence of the –GGX– and –GPG– motifs in its sequence. In contrast to the passive role assigned to polyalanine nanocrystals in MAS, polyglycine II nanocrystals can undergo growing/collapse processes that contribute to increase toughness and justify the ability of Flag to supercontract.

Nanoscale X-Ray Diffraction of Silk Fibers

“…We note that morphologies based on ordered skin-layers and a more disordered core, providing a balance of strength and toughness, are well-known for synthetic polymeric fibers (Müller et al, 2000;Liu et al, 2014). PG-II nanodomains have only recently been suggested as functional elements, reinforcing flagelliform silk fibers (Perea et al, 2013). S,S * reflections observed for MaS fibers are probably also based on PG-II nanodomains.…”

“…Systematic studies of nanoscale heterogeneities across the spider phylogeny should shed light on the presence and local distribution of β-sheet, PG-II and possibly other nanocrystalline inclusions. Potential targets are βtype nanodomains in Argiope decorating fibers (Figure 7B), the probably ribbon-like morphology of Eriophora MiS fibers ) and PG-II nanodomains in several flagelliform silks probed by microXRD (Craig, 2003;Perea et al, 2013). Such studies could also contribute to an understanding of the nature of graphene and single-walled carbon nanotubes inclusions in spiders MaS and silkworm fibroin fibers (Wang et al, 2014(Wang et al, , 2016Lepore et al, 2017).…”

Silk–Its Mysteries, How It Is Made, and How It Is Used

“…40,41 Recently, it was shown that amorphous phase containing GGX and GPG motifs can take up polyglycine II nanocrystal structure. 140 Moreover, different types of similar secondary structures result in alternating mechanical properties. For example, in dragline silks, the tensile strength of the silk fiber is controlled by the silk primary structure, which in turn dictates the strength of interactions between β-sheets.…”

Humidity‐dependent mechanical and adhesive properties of Arachnocampa tasmaniensis capture threads

“…The presence of water can greatly reduce T g as water is a known plasticizer and promotes molecular mobility (Sperling, 2005). Not surprisingly, many invertebrate silks, such as silkworm cocoon silk (P erez-Rigueiro et al, 2000;Plaza et al, 2008), lacewing silk egg stalks (Bauer et al, 2012), caddisfly net silk (Tsukada et al, 2010) and various spider silks (Gosline, Denny & DeMont, 1984;Shao, Young & Vollrath, 1999) as well as mussel byssus (Smeathers & Vincent, 1979;Troncoso, Torres & Grande, 2008), become rubberized when exposed to water, as stiffness (Young's modulus) is reduced and extensibility (breaking strain) is increased. This softening effect is believed to be the result of water molecules disrupting intermolecular hydrogen bonds (Termonia, 1994;Bauer et al, 2012).…”