Structural analysis of silk with 13C NMR chemical shift contour plots.
The polymorphic structures of silk fibroins in the solid state were examined on the basis of a quantitative relationship between the 13C chemical shift and local structure in proteins. To determine this relationship, 13C chemical shift contour plots for C alpha and C beta carbons of Ala and Ser residues, and the C alpha chemical shift plot for Gly residues were prepared using atomic co-ordinates from the Protein Data Bank and 13C NMR chemical shift data in aqueous solution reported for 40 proteins. The 13C CP/MAS NMR chemical shifts of Ala, Ser and Gly residues of Bombyx mori silk fibroin in silk I and silk II forms were used along with 13C CP/MAS NMR chemical shifts of Ala residues of Samia cynthia ricini silk fibroin in beta-sheet and alpha-helix forms for the structure analyses of silk fibroins. The allowed regions in the 13C chemical shift contour plots for C alpha and C beta carbons of Ala and Ser residues for the structures in silk fibroins, i.e. Silk II, Silk I and alpha-helix, were determined using their 13C isotropic NMR chemical shifts in the solid state. There are two area of the phi,psi map which satisfy the observed Silk I chemical shift data for both the C alpha and C beta carbons of Ala and Ser residues in the 13C chemical shift contour plots.
Asakura
T
T
Department of Biotechnology, Tokyo University of Agriculture and Technology, Koganei, Japan. asakura@cc.tuat.ac.jp
Iwadate
M
M
Demura
M
M
Williamson
M P
MP
D000409:Alanine / Q000737:chemistry; D000596:Amino Acids / Q000737:chemistry*; D000818:Animals; D012831:Bombyx / Q000737:chemistry; D016208:Databases, Factual; D005998:Glycine / Q000737:chemistry; D019476:Insect Proteins / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D011487:Protein Conformation; D012694:Serine / Q000737:chemistry; D047011:Silk
D000596:Amino Acids; D019476:Insect Proteins; D047011:Silk; D012694:Serine; D000409:Alanine; D005998:Glycine