Structural Disorder in Silk Proteins Reveals the Emergence of Elastomericity

Abstract

Spider silks combine basic amino acids into strong and versatile fibers where the quality of the elastomer is attributed to the interaction of highly adapted protein motifs with a complex spinning process. The evaluation, however, of the interaction has remained elusive. Here, we present a novel analysis to study silk formation by examining the secondary structures of silk proteins in solution. Using the seven different silks of Nephila edulis as a benchmark system, we define a structural disorder parameter (the folding index, gamma). We found that gamma is highly correlated with the ratio of glycine present. Testing the correlation between glycine content and the folding index (gamma) against a selected range of silks, we find quantitatively that, in order to achieve specialization with changes in mechanical performance, the spider's silks require higher structural flexibility at the expense of reduced stability and consequently an increased conversion-energy cost. Taken together, our biophysical and evolutionary findings reveal that silk elastomericity evolved in tandem with specializations in the process of silk spinning.

Spiders spinning electrically charged nano-fibres

“…During their history of 400þ years, spider silks have evolved an interesting and presumably highly adapted combination of molecular composition and processing conditions [15]. We found that the cribellum glands studied have long ducts but lack the internal draw-down so characteristic for other long ducts, where the silk is already a thread when it reaches the spigot [10,16].…”

Diversity of Molecular Transformations Involved in the Formation of Spider Silks

“…14 The environment of the solution along the duct (pH and ionic gradients) is also important, as it promotes protein-protein interactions. 15,16 It is thus expected that the anatomical diversity and physicochemical parameters of the glands are associated with differing spinning processes. In this respect, Dicko et al proposed an interesting relation between the degree of disorder of spider silk proteins and the complexity of the spinning apparatus.…”

“…In this respect, Dicko et al proposed an interesting relation between the degree of disorder of spider silk proteins and the complexity of the spinning apparatus. 15 The viscoelastic dope itself, in particular its rheological properties, is critical for the spinning mechanism. As a matter of fact, the sericigene solution has a liquid crystalline (i.e., of non-Newtonian nature) that gives it shear-thinning properties that facilitate the spinning process.…”

Parasitoid suppression and life-history modifications in a wolf spider following infection by larvae of an acrocerid fly

“…However, the mechanical and biochemical diversity of silks is staggering. Spiders are unique in their reliance on silk throughout their lives, their diverse uses of silk, and their production of toolkits of as many as seven or eight different types of silks, each of which has a unique chemical composition and comes from its own discrete gland(s) and associated spigot(s) (Guerette et al 1996;Blackledge & Hayashi 2006a;Vollrath & Porter 2006;Dicko et al 2008). Most spider silk proteins are encoded by members of the spidroin gene family, whose evolutionary history is characterized by bouts of gene duplication followed by strong diversification (Gatesy et al 2001;Gaines & Marcotte 2008;Garb et al 2010).…”