Self-tensioning aquatic caddisfly silk: Ca(2+)-dependent structure, strength, and load cycle hysteresis.

Biomacromolecules

PubMedID: 24050221

Ashton NN, Roe DR, Weiss RB, Cheatham TE, Stewart RJ. Self-tensioning aquatic caddisfly silk: Ca(2+)-dependent structure, strength, and load cycle hysteresis. Biomacromolecules. 2013;.
Caddisflies are aquatic relatives of silk-spinning terrestrial moths and butterflies. Casemaker larvae spin adhesive silk fibers for underwater construction of protective composite cases. The central region of Hesperophylax sp. H-fibroin contains a repeating pattern of three conserved sub-repeats, all of which contain one or more (SX)n motifs with extensively phosphorylated serines. Native silk fibers were highly extensible, and displayed a distinct yield point, force plateau, and load cycle hysteresis. FTIR spectroscopy of native silk showed a conformational mix of random coil, ß-sheet, and turns. Exchanging multivalent ions with Na(+) EDTA disrupted fiber mechanics, shifted the secondary structure ratios from anti-parallel ß-sheet toward random coil and turns, and caused the fibers to shorten, swell in diameter, and disrupted fiber birefringence. The EDTA effects were reversed by restoring Ca(2+). Molecular dynamic simulations provided theoretical support for a hypothetical structure in which the (pSX)n motifs may assemble into two- and three-stranded, Ca(2+)-stabilized ß-sheets.