Determination of Local Structure of C-13 Selectively Labeled 47-mer Peptides as a Model for Gly-Rich Region of Nephila clavipes Dragline Silk Using a Combination of C-13 Solid-State NMR and MD Simulation

T Asakura and A Nishimura and Y Tasei, MACROMOLECULES, 51, 3608-3619 (2018).

DOI: 10.1021/acs.macromol.8b00536

For the first time, we elucidate the complex structure of the Gly-rich regions in Nephila clavipes dragline silk through synergistic experimental and theoretical studies. First, the C-13 selectively labeled 47-mer peptides selected from the glycine (Gly)rich region of N. clavipes dragline silk were synthesized. The C-13 CP/MAS NMR spectra were analyzed to determine the fractions of the conformations of individual Gly and Ala residues through C-13 conformation-dependent chemical shifts and peak deconvolution. By comparing the C-13 solid- state NMR spectra of several simple model peptides, the presence of 3(1) helix in the 47-mer peptides was disproved, and the (Ala)(6) regions were shown to form) beta-sheet structure in the staggered arrangement. Although the fraction of beta-sheet components tended to increase and the fraction of random coil component decrease toward both chain ends, significant change in the fractions was observed depending on the amino acid position. These results were successfully rationalized through molecular dynamics simulation.

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