Probing the elastic nature of spider silk in pursuit of the next designer fiber.

Spider silk, one of nature's greatest accomplishments, has a combination of strength and elasticity that is unrivaled. Spiders produce up to 7 different silks; each one with a unique combination of tensile strength and elasticity that allows the spiders' web to hold prey while being resilient enough not to break upon impact. In an attempt to determine the sequences responsible for these enviable mechanical properties, several different amino acid motifs have been defined. Much of the recent work is now concentrated on correlating amino acid motifs with a specific mechanical property. The current hypothesis is that the strength property of spider silk is conferred by a poly-alanine or alanine rich (An or GAn) motif whereas the elastic nature of spider silk is conferred by the amino acid motif, GPGXX, where X is Q, S, A, G, or Y. Despite the fact that these different motifs are now known, the combination of strength and elasticity are yet to be duplicated ex vivo. In an attempt to verify that the GPGXX motif imparts elasticity to the spider silk, the number of repeats and/or the amino acid composition of the Argiope aurantia "elastic motif" were varied and expressed in various strains of E. coli to change the elastic properties of the resulting film and/or fiber. Concurrent with work on the elasticity motif is ongoing work on the strength module. Understanding these two different motifs will aide efforts to produce a designer biomaterial for medical, commercial, and military applications.