Supercontraction and Backbone Dynamics in Spider Silk:  ¹³C and ²H NMR Studies

Abstract

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.

Physical characterization of functionalized spider silk: electronic and sensing properties

“…The effects of hydration decrease the intensity of most of the peaks except for the two Ala peaks, Ala C α and Ala C β (β-sheet), which are generally attributed to the poly-Ala located in the β-sheet crystal-forming blocks. The overall intensity decrease of the spectra in the hydrated sample is thought to result from the increasing mobility of the protein backbone and side-chain mobility with hydration [22,23]. Of the affected peaks, the largest intensity drops were observed for the glycine (Gly) C α , and glutamate or glutamine (both labeled as Glx), serine (Ser) and proline (Pro) peaks.…”

The elaborate structure of spider silk

“…This process is important to ensure the rigidity of the spider's web during its lifetime and is thought to be caused by the organization and arrangement of individual silk proteins. 53,54 Spider silk vs insect silk. Spider silk is often compared to insect silk, preferably taken from the silkworm Bombyx mori.…”

High‐resolution NMR characterization of a spider‐silk mimetic composed of 15 tandem repeats and a CRGD motif

“…Interestingly, Jelinski and coworkers determined that super contraction of major ampullate dragline-silk of N. clavipes, corresponded to the consensus sequence, YGGLGS(N)QGAGR. 54 Additionally, it was suggested that substitution to an analogous, but less hydrophilic sequence might attenuate the contraction of silk in water. The engineered CRGD-silk sequence incorporates the YGGLGSQG repeat sequence, which corresponds to the indicated modification, and suggests a possible explanation for our observation.…”