Changes in the Local Structure of Nephila clavipes Dragline Silk Model Peptides upon Trifluoroacetic Acid, Low pH, Freeze-Drying, and Hydration Treatments Studied by 13C Solid-State NMR.

Abstract

The conformational analysis of spider dragline silks is difficult because of the amorphous character of the silks. In this article, the fractions of several conformations were determined for three 47-mer peptides, (Glu)4(Ala)6GlyGly12Ala13Gly14GlnGlyGlyTyrGlyGlyLeuGlySerGlnGly25Ala26Gly27-ArgGlyGlyLeuGlyGlyGlnGly35Ala36Gly37(Ala)6(Glu)4, with three underlined 13C-labeled blocks using a 13C CP/MAS NMR method. The conformations of the 13C-labeled sites change significantly depending on the location of the labeled blocks when treated with trifluoroacetic acid, low pH, and freeze-drying. The conformations of Ala36 and Gly37 residues are strongly influenced by the specific conformation of the (Ala)6 sequence at the C-terminal side, but those of other residues, Ala13 and Gly14, and Ala 26 and Gly27, are basically not influenced by the conformations of (Ala)6. Through hydration of the β-sheet peptide, sharp peaks with random coil could be observed depending on the position of the residue, and this result could be interpreted via the change in the Ramachandran map obtained from the molecular dynamics simulation.