Reversible assembly of β-sheet nanocrystals within caddisfly silk

J. Bennett Addison, Warner S. Weber, Qiushi Mou, Nicholas N. Ashton, Russell J. Stewart, Gregory P. Holland, Jeffery Yarger

Research output: Contribution to journalArticle

17 Scopus citations

Abstract

Nuclear magnetic resonance (NMR) and X-ray diffraction (XRD) experiments reveal the structural importance of divalent cation-phosphate complexes in the formation of β-sheet nanocrystals from phosphorylated serine-rich regions within aquatic silk from caddisfly larvae of the species Hesperophyla consimilis. Wide angle XRD data on native caddisfly silk show that the silk contains a significant crystalline component with a repetitive orthorhombic unit cell aligned along the fiber axis with dimensions of 5.9 Å × 23.2 Å × 17.3 Å. These nanocrystalline domains depend on multivalent cations, which can be removed through chelation with ethylenediaminetetraacetic acid (EDTA). A comparison of wide angle X-ray diffraction data before and after EDTA treatment reveals that the integrated peak area of reflections corresponding to the nanocrystalline regions decreases by 15-25% while that of the amorphous background reflections increases by 20%, indicating a partial loss of crystallinity. 31P solid-state NMR data on native caddisfly silk also show that the phosphorylated serine-rich motifs transform from a rigid environment to one that is highly mobile and water-solvated after treatment with EDTA. The removal of divalent cations through exchange and chelation has therefore caused a collapse of the β-sheet structure. However, NMR results show that the rigid phosphorus environment is mostly recovered after the silk is re-treated with calcium. The 31P spin-lattice (T1) relaxation times were measured at 7.6 ± 3.1 and 1 ± 0.5 s for this calcium-recovered sample and the native silk sample, respectively. The shorter 31P T1 relaxation times measured for the native silk sample are attributed to the presence of paramagnetic iron that is stripped away during EDTA chelation treatment and replaced with diamagnetic calcium.

Original languageEnglish (US)
Pages (from-to)1269-1275
Number of pages7
JournalBiomacromolecules
Volume15
Issue number4
DOIs
StatePublished - Apr 14 2014

    Fingerprint

ASJC Scopus subject areas

  • Bioengineering
  • Biomaterials
  • Polymers and Plastics
  • Materials Chemistry

Cite this

Addison, J. B., Weber, W. S., Mou, Q., Ashton, N. N., Stewart, R. J., Holland, G. P., & Yarger, J. (2014). Reversible assembly of β-sheet nanocrystals within caddisfly silk. Biomacromolecules, 15(4), 1269-1275. https://doi.org/10.1021/bm401822p