Packing Structure of Antiparallel beta-Sheet Polyalanine Region in a Sequential Model Peptide of Nephila clavipes Dragline Silk Studied Using C-13 Solid-State NMR and MD Simulation

T Asakura and A Nishimura and A Aoki and A Naito, BIOMACROMOLECULES, 20, 3884-3894 (2019).

DOI: 10.1021/acs.biomac.9b00969

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)(4)GlyGlyLeuGly GlyGlnGlyAlaGly(Ala)(n)GlyGlyAlaGlyGlnGlyGlyTyrGlyGly(Glu)(4) (n = 3-8) using C-13 solid-state NMR spectroscopy. The conformations of (Ala)(n) in the freeze-dried peptides changed gradually with increasing n from random coils to alpha-helices with partial antiparallel beta-sheet (AP- beta) structures. Conversely, all the insolubilized peptides, n = 6-8 after low-pH treatment and n = 4-8 after formic acid/methanol treatment, formed AP-beta structures with significant amounts of staggered packing arrangements. These results are different from previously obtained results for pure alanine oligopeptides, that is, AP-beta (Ala)(n) formed rectangular packing for less than n = 6 but staggered packings for n >= 7. The C-13-labeled peptides were also used to confirm the staggered packing arrangements from NMR dynamics. Furthermore, a MD simulation supported the observed results.

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