Modular Spider Silk Fibers: Defining New Modules and Optimizing Fiber Properties

Orb-web weaving spiders use multiple silk fibers to accomplish different tasks, combining repetitive peptide modules to produce different properties in each fiber. Each fiber is the product of a distinct gland, but is subject to a common spinning paradigm to produce an insoluble fiber from an aqueous-soluble protein dope. We start by presenting the cloning of the last of the six silks used by Nephila clavipes, the piriform silk spidroin. This piriform fiber presents a unique set of protein modules, which are used to attach other silk fibers to surfaces and to each other. Fiber spinning studies using major ampullate, minor ampullate, and flagelliform modules responsible for distinct secondary structures and therefore fiber properties will be presented. The properties of various synthetic fibers such as the initial (Young’s) modulus, tensile strength at break, strain at break, and toughness will be presented for a N. clavipes flagelliform/major ampullate hybrid synthetic fiber series, and an Argiope aurantia flagelliform/major ampullate hybrid synthetic fiber. Then, an N. clavipes major ampullate protein 1 synthetic fiber will be compared to itself in terms of how the fiber reacts to a post-spin draw in terms of properties and secondary structure. Finally, two flagelliform/major ampullate hybrid fibers made from slightly different elastic modules will be compared to show how minor changes in a single peptide module can change artificial spinning parameters substantially. Post-spin draw regimens on each fiber will demonstrate the importance of such procedures in optimizing fiber properties to take advantage of the modular protein sequences. Secondary structure studies at different stages of spinning will demonstrate the recruitment of secondary structures that greatly influence fiber properties.