Packing Structure of Antiparallel β-sheet Polyalanine Region in a Sequential Model Peptide of Dragline Silk Studied Using C Solid-State NMR and MD simulation.

Abstract

The packing structures of polyalanine regions, which are considered to be the reason for the extremely high strength of spider dragline silks, were studied using a series of sequential peptides: (Glu)GlyGlyLeuGlyGlyGlnGlyAlaGly(Ala)nGlyGlyAlaGlyGlnGlyGlyTyrGlyGly(Glu) (n = 3-8) using C solid-state NMR spectroscopy. The conformations of (Ala) in the freeze-dried peptides changed gradually with increasing n from random coils to α-helices with partial antiparallel β-sheet (AP-β) structures. Conversely, all the insolubilized peptides, n = 6-8 after low-pH treatment and n = 4-8 after formic acid/methanol treatment, formed AP-β structures with significant amounts of staggered packing arrangements. These results are different from previously obtained results for pure alanine oligopeptides, i.e., AP-β (Ala) formed rectangular packing for less than n = 6 but staggered packings for n ≥ 7. The C-labeled peptides were also used to confirm the staggered packing arrangements from NMR dynamics. Furthermore, MD simulation supported the observed results.