Ubiquitous distribution of salts and proteins in spider glue enhances spider silk adhesion

Abstract

Modern orb-weaving spiders use micron-sized glue droplets on their viscid silk to retain prey in webs. A combination of low molecular weight salts and proteins makes the glue viscoelastic and humidity responsive in a way not easily achieved by synthetic adhesives. Optically, the glue droplet shows a heterogeneous structure, but the spatial arrangement of its chemical components is poorly understood. Here, we use optical and confocal Raman microscopy to show that salts and proteins are present ubiquitously throughout the droplet. The distribution of adhesive proteins in the peripheral region explains the superior prey capture performance of orb webs as it enables the entire surface area of the glue droplet to act as a site for prey capture. The presence of salts throughout the droplet explains the recent Solid-State NMR results that show salts directly facilitate protein mobility. Understanding the function of individual glue components and the role of the droplet's macro-structure can help in designing better synthetic adhesives for humid environments.

Loss of Phosphate Determines the Versatility of a Spider Orb-web Glue Ball

“…According to recent reports, the main components of the glue ball are glycoproteins [9][10][11] and salt. 3,[12][13][14][15][16][17][18][19] Two potential structural mechanisms have been previously suggested. The first suggests that concentrated glycoprotein is wrapped in a salt-and-water shell.…”

Ultrastructure of spider thread anchorages

“…Liquid components, that appeared less electron dense and occasionally formed droplets might be concentrated solutions of salts, as indicated by large amounts of crystals appearing in cavities between the filamentous components of the glue layer in fractured piriform threads (Wolff, Řezá c, et al, 2017). The importance of glycoproteins and salts is well described from the secretion of the aggregate silk glands that produce the tacky droplets on the capture threads in orb and cobweb spiders (Amarpuri, Chaurasia, Jain, Blackledge, & Dhinojwala, 2015;Sahni et al, 2014;Townley & Tillinghast, 2013). In these the salts adsorb water, thereby soften the glue and enhance adhesion by the solvation of the glycoproteins (Amarpuri et al, 2015, Sahni et al, 2014.…”

“…The importance of glycoproteins and salts is well described from the secretion of the aggregate silk glands that produce the tacky droplets on the capture threads in orb and cobweb spiders (Amarpuri, Chaurasia, Jain, Blackledge, & Dhinojwala, 2015;Sahni et al, 2014;Townley & Tillinghast, 2013). In these the salts adsorb water, thereby soften the glue and enhance adhesion by the solvation of the glycoproteins (Amarpuri et al, 2015, Sahni et al, 2014. In attachment discs, the carbohydrate side chains of glycol-proteins may have the function to anchor into grooves and striations of the substrate establishing strong adhesion.…”

On Modulating Interfacial Structure towards Improved Anti-Icing Performance

“…While anions have the stronger impact in the behaviors listed in Figure 19A, counter-ion solvation also leads to differentials in biomacromolecular adsorption ( Figure 19B) which can be expressed in terms of adsorption energies, conformational changes, and adhesive properties [175][176][177][178][179]. The effect on coagulation of polystyrene latex particles for both anions and cations [180] is shown in Figure 19C.…”