The mechanical properties of spider silk are determined by the genetic regulation of fibroin proteins and chemical and physical processing during spinning

Paul André Guerette
Orb-web building spiders produce a functional variety of fibrous silks that exhibit a range in mechanical properties from Kevlar-like super fibers to rubber-like elastomeric fibers. The mechanisms of silk property control employed by the orb-spider were formerly not known, but were hypothesised to be related to the chemical sequence design of their fibers constituent fibroin proteins and the chemical and physical conditions of fiber spinning. The genome of the orb-spider Araneus diadematus was
more » ... eus diadematus was found to contain members of at least one fibroin gene family which encode proteins containing different proportions of crystal forming poly(alanine) domains and glycine rich amorphous domains. The fibroin genes were found to be expressed differentially in the spiders seven different gland types, indicating that transciptional regulation affords the spider the ability to produce a variety of gland-specific, compositionally distinct silk secretions that are predicted to have different crystallization potentials. Qualitative polarized light microscopy supports this prediction by showing that distinct glandular secretions crystallize differentially under identical shear conditions in the lab. The results therefore indicate that genetic regulation of fibroin genes affords the orb-spider the potential to modulate the mechanical properties of its large repertoire of silks. Chemical micro-environment and physical draw processing conditions were also hypothesised to influence the mechanical properties of orb-spider silk. In the orb-web, the rubber-like native viscid (FL) silk is subject to a distinct chemical micro-environment provided by an inter-penetrating aqueous glue coating that contains water, salts, free amino acids and several water soluble Low Molecular Weight (LMW) compounds. The glue coating was removed by a water wash:dry process in the lab, and the processed FL fibers exhibited an increase in Birefringence and a change in mechanical properties indicative of the development increased supra-molecular [...]
doi:10.14288/1.0099210 fatcat:sr6jdihhbjhmbbvufjzbuplwcy