The major ampullate glands of the spider Nephila clavipes contain approximately 0.2 microliter each of a highly concentrated (approximately 50%) solution of silk fibroin. Therefore, the reservoir of silk in these glands presents an ideal opportunity to observe prefolded conformations of a protein in its native state. To this end, the structure and conformation of major ampullate gland silk fibroin within the glands of the spider N. clavipes were examined by 13C NMR spectroscopy. These results were compared to those from silk protein first drawn from the spinneret and then denatured. The 13C NMR chemical shifts, along with infrared and circular dichroism data, suggest that the silk fibroin in the glands exists in dynamically averaged helical conformations. Furthermore, there is no evidence of proline residues in U-(13)C-D-glucose-labeled silk. This transient prefolded "molten fibril" state may correspond to the silk I form found in Bombyx mori silk. There is no evidence of the final beta-sheet structure in the ampullate gland silk fibroin before final silk processing. However, the conformation of silk in the glands appears to be in a highly metastable state, as plasticization with water produces the beta-sheet structure. Therefore, the ducts connecting the ampullate glands to the spinnerets play a larger role in silk processing than previously thought.

Spider dragline silk is Nature's high-performance protein fiber. This biomaterial has attracted much interest from scientists in various disciplines since it has become feasible to produce spider silk proteins by means of biotechnology. This article reports on research directed toward the regeneration of spider silk. A procedure is describedsincluding spinning and postspinning processings that produces fibers with promising mechanical properties from dissolved natural spider dragline silk. Tensile tests and structural characterization of the regenerated fibers illustrate correlations between the macroscopic and microscopic properties of the final material and between these properties and the fiber's processing history. Results point to the importance of an aqueous environment in the annealing of structure. The revealed structure-property relationships are expected to be of fundamental importance for the future design of man-made protein products.

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