Testing for Protein Composition-Dependent Variation of Recombinant Pyriform Silk Fibre Mechanics

Abstract

Orb-weaver spiders produce protein-based silks, including Pyriform silk which creates attachment discs and comprises pyriform spidroin 1 and 2 (PySp1 and PySp2). The recombinant pyriform spider silk proteins HPy1 and HPy2 are composed of a single repeat unit or a tandem-repeat of two units from the PySp1 repetitive domain from Argiope argentata, respectively. Previously, improved mechanical properties were observed for wet-spun HPy2 fibres of protein expressed in amino acid-supplemented M9 medium compared to LB medium, leading to the hypothesis that decreased mechanical performance was due to truncated HPy2. This thesis tests the effect of increasing amounts of truncated protein on fibre mechanics. Specifically, fibres were wet-spun using pure HPy2, two mixtures of HPy1 and HPy2, and pure HPy1. Tensile testing demonstrated that fibres formed with increasing proportions of HPy2 to HPy1 had improved mechanics. Conversely, protein secondary structuring was unaffected, with a transition from alpha-helix-rich to beta-sheet-rich states from solution to fibre regardless of protein composition.