Solid‐state NMR relaxation studies of Australian spider silks

Abstract

Solid-state NMR techniques were used to study two different types of spider silk from two Australian orb-web spider species, Nephila edulis and Argiope keyserlingi. A comparison of (13)C-T(1) and (1)H-T(1rho) solid-state NMR relaxation data of the Ala Calpha, Ala Cbeta, Gly Calpha, and carbonyl resonances revealed subtle differences between dragline and cocoon silk. (13)C-T(1rho) and (1)H-T(1) relaxation experiments showed significant differences between silks of the two species with possible structural variations. Comparison of our data to previous (13)C-T(1) relaxation studies of silk from Nephila clavipes (A. Simmons et al., Macromolecules, 1994, Vol. 27, pp. 5235-5237) also supports the finding that differences in molecular mobility of dragline silk exist between species. Interspecies differences in silk structure may be due to different functional properties. Relaxation studies performed on wet (supercontracted) and dry silks showed that the degree of hydration affects relaxation properties, and hence changes in molecular mobility are correlated with functional properties of silk.

Orientational order of Australian spider silks as determined by solid‐state NMR

“…Proton and carbon NMR relaxation times have shown differences in molecular mobility between types of silk (dragline versus cocoon) and between species (Nephila versus Argiope) and may reflect the relationship between molecular structure and biological function. 32 Our new 13 C and 15 N NMR results using silk, derived from spiders maintained on labeled Gly and Ala amino acid diets, have revealed further differences in the crystalline, amorphous, and oriented amorphous phases of dragline silk between species, which may correlate with the different physical properties of the materials.…”

“…Proton and carbon NMR relaxation times show differences in molecular mobility between types of silk (dragline versus cocoon) and between species (Nephila edulis versus Argiope keyserlingi) 32 and most probably reflect differences in molecular structure related to biological function. We have extended these studies and now report 13 C and 15 N NMR results using oriented dragline silk from two species of spiders fed on labeled Gly and Ala amino acids to determine differences in the amount of crystalline and amorphous phases.…”

Studying natural structural protein fibers by solid‐state nuclear magnetic resonance

“…This was done for elastin (106), an elastin-like polypeptide (105), Lepidoptera cocoon silks (107), and spider silk (108, 109) for example. T 1 and T 1r can also reveal motional differences within fibers produced by different species (107,108).…”

“…Both 1 H-and 13 C-T 1 relaxation times are measured via 13 C signals since 1 H spectra cannot be obtained with sufficient resolution. The inversion-recovery experiment normally used in liquid-state NMR to measure T 1 is thus modified to include a cross-polarization step (108,110). The same applies to T 1r values; 1 H-T 1r are obtained by a simple CP with variable contact time followed by 13 C detection, and 13 C-T 1r by a classical crosspolarization step followed by a variable 13 C spin-lock time prior to its detection (108).…”

“…The inversion-recovery experiment normally used in liquid-state NMR to measure T 1 is thus modified to include a cross-polarization step (108,110). The same applies to T 1r values; 1 H-T 1r are obtained by a simple CP with variable contact time followed by 13 C detection, and 13 C-T 1r by a classical crosspolarization step followed by a variable 13 C spin-lock time prior to its detection (108). To select protons which are directly bonded to the observed 13 C, the cross-polarization step was replaced in a recent work by a Lee-Goldburg CP which reduces spin diffusion effects (105).…”