Journal
MACROMOLECULAR BIOSCIENCE
Volume 4, Issue 3, Pages 175-185Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/mabi.200300098
Keywords
biopolymers; alpha-helix; NMR; Samia cynthia ricini; silk fibroin
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The structure of silk fibroin from a wild silkworm, S. C. ricini, the amino acid sequence of which consists of repeated poly-Ala and Gly-rich regions, was examined by using solution and solid-state NMR methods. The structural transition of the silk fibroin in aqueous solution was monitored by using C-13 solution NMR spectroscopy as a function of temperature. The fast exchange with respect to the chemical shift between the helix and coil conformations was observed in the poly-Ala region and the slow conformational change from alpha-helix to random coil was observed for the Gly residue adjacent to the N-terminal Ala residue of the poly-Ala region. The torsion angles of several Ala and Gly residues in the model peptide, GGAGGGYGGDGG(A)(12)GGA-GDGY-GAG, were determined by the conformation-dependent C-13 chemical shifts, rotational echo double resonance (REDOR) and 2D spin-diffusion NMR methods. The solid-state NMR analysis leads to the precise silk structure before spinning, where the poly-Ala sequence takes a typical alpha-helix pattern with a tightly winded helical structure at both terminal regions of the poly-Ala sequence. This is expected to stabilize the alpha-helical structure of the poly-Ala region in S. c. ricini silk fibroin from the silkworm.
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