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.

As part of a general study of the structure of spider silk fibers, major ampullate gland silk fibers were collected from Nephila clavipes spiders, and SAXS patterns were obtained from loops of fibers under a variety of conditions. Two orders of lamellar reflection were seen, with a long spacing of 8.4 nm. This increased reversibly by 4% when the fiber was stretched by 10% and shrank to 5.8 nm when the fiber itself shrank 45% on wetting. A strong equatorial streak had a bimodal orientation distribution similar to that seen in NMR and WAXD. The sharper component had a lateral size scale (radius of gyration) of 2.5 nm and a misorientation of 10° FWHM, similar to the orientation of the crystals. The minimum breadth of the streak indicates that the scattering objects are 0.1 μm long. There is an isotropic central scattering, probably caused by voids. On wetting, the lamellar peaks became more intense; more dramatically, the equatorial scattering strengthens and extends to higher angles, almost halving the lateral size scale to 1.4 nm. An equatorial maximum appears at a spacing of 6 nm, indicating a degree of order in the fibrillar structure.