The high-performance mechanical properties of certain spider silks can be radically altered by the addition of water. For example, unconstrained silk fibers from the major ampullate gland of the golden orbweaving spider, Nephila claVipes, contract to about half of their original length when immersed in water. In this paper we use solid-state 13 C and 2 H NMR to study N. claVipes silk fibers, so as to address the molecular origins of supercontraction in the wet silk. Using 13 C NMR, we study backbone dynamics and demonstrate that, when in contact with water, a substantial fraction of the glycine, glutamine, tyrosine, serine, and leucine residues in the protein backbone show dramatic increases in the rate of large-amplitude reorientation. 2 H NMR of silk samples that incorporate leucine deuterated at one terminal methyl group provides a probe for dynamics at specific side chains along the fiber. Only a subset of these leucine residues is strongly affected by water. We suggest that the highly conserved YGGLGS(N)QGAGR blocks found in the silk protein play a major role in the supercontraction process. Amino acid sequences are proposed to produce artificial spider silk with similar mechanical properties, but without the undesired phenomenon of supercontraction. A possible use of the "supercontracting sequence" is also suggested.

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.

A microfabricated spinneret is described that is capable of spinning meters of fibers from solutions containing as little as 10 mg of purified protein. Using the spinneret, regenerated Bombyx mori fibers were made using various processing parameters. A log-linear relationship was found between the maximum stress sustained by the regenerated fibers and their diameters. Solid state 13 C NMR was used to determine the effects of spinneret diameter and postspinning draw ratio on the secondary structure of the alanine residues in the silk protein. The relationship between the secondary structure of the alanine residues and the maximum stress of the silks was also examined. The results suggest that a relatively high fraction of the alanine residues in the silks must be in the -sheet conformation (>65%) in order to produce the highest stress fibers. However, the fraction of alanine residues in the -sheet conformation does not uniquely determine the maximum stress of a fiber; it is suggested that orientation of these -sheets is also an important parameter.