Structural Investigations of Supercontracted Spider Dragline Silk

Abstract

Spider dragline silk is a semicrystalline polymer of great interest in materials science due to its unique mechanical properties and biocompatibility. Spun from the major ampullate glands, this type of silk possesses an exceptional combination of elasticity, strength and toughness. At the molecular level, spider silk is composed of fibrous proteins organized into crystalline nanodomains embedded in an amorphous matrix. In the presence of liquid water or high humidity, the amorphous phase is plasticized and its hydrogen bonding network disrupted, which results in the shrinking of the fiber up to 50% of its initial length. This phenomenon, known as supercontraction, is triggered by the entropic folding of the polypeptide chains resulting from the water-induced increase in chain mobility. However, disagreements exist in the literature as to whether a change in the secondary structure of the protein occurs or not during supercontraction. Furthermore, although it has already been established that supercontraction induces a disorientation of the molecular units, this effect has not been quantified yet. Therefore, we will investigate and quantify, for different species, the conformational and orientational variations of the silk proteins induced by supercontraction. To achieve our goals, we will use Raman spectromicroscopy, a technique that as long been proven to be a useful tool to probe silk. Moreover, the effects of drawing speed on the magnitude of supercontraction will also be examined.