Structure and structural changes of the silk fibroin from Samia cynthia ricini using nuclear magnetic resonance spectroscopy.
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 13C 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)12GGA-GDGYGAG, were determined by the conformation-dependent 13C 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.
Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan. asakura@cc.tuat.ac.jp
Tetsuo
T
Asakura
Yasumoto
Y
Nakazawa
D000596:Amino Acids / Q000737:chemistry; D000818:Animals; D012831:Bombyx / Q000737:chemistry* / Q000378:metabolism; D005349:Fibroins / Q000737:chemistry*; D019476:Insect Proteins / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D017433:Protein Structure, Secondary
D000596:Amino Acids; D019476:Insect Proteins; D005349:Fibroins