A repeated beta-turn structure in poly(Ala-Gly) as a model for silk I of Bombyx mori silk fibroin studied with two-dimensional spin-diffusion NMR under off magic angle spinning and rotational echo double resonance.
The structure of a crystalline form of Bombyx mori silk fibroin, commonly found before the spinning process (known as silk I), was proposed by combining data obtained from two-dimensional spin-diffusion nuclear magnetic resonance under off magic angle spinning, rotational-echo double-resonance (REDOR), previously reported X-ray diffraction analyses and 13C NMR chemical shifts. Instead of B. mori silk fibroin with silk I structure, we used the sequential model peptide (Ala-Gly)15. The structure of the sequential model peptide is characterized as silk I after dissolving the peptide in 9 M LiBr and then dialyzing against water. Moreover, 13C or 15N-labeled sites may be introduced easily at any position in (Ala-Gly)(15) by the solid phase synthesis method for these NMR experiments. The torsional angles of (Ala-Gly)15 with silk I structure were determined as (-60(+/-5) degrees, 130(+/-5) degrees ) and (70(+/-5) degrees, 30(+/-5) degrees ) for Ala and Gly residues, respectively. The formation of the intra-molecular hydrogen bonding along the chain was confirmed from REDOR NMR by determination of the inter-atomic distance between the nitrogen and carbon atoms comprising the intra-molecular hydrogen bonding. The structure is named a repeated beta-turn type II-like structure.
Asakura
T
T
Department of Biotechnology, Tokyo University of Agriculture and Technology, Tokyo, Koganei, 184-8588, Japan. asakura@cc.tuat.ac.jp
Ashida
J
J
Yamane
T
T
Kameda
T
T
Nakazawa
Y
Y
Ohgo
K
K
Komatsu
K
K
D000409:Alanine / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D012831:Bombyx / Q000737:chemistry*; D003956:Dialysis; D004058:Diffusion; D005349:Fibroins / Q000737:chemistry*; D005998:Glycine / Q000737:chemistry / Q000378:metabolism; D006860:Hydrogen Bonding; D019476:Insect Proteins / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D012399:Rotation; D047011:Silk; D014867:Water / Q000378:metabolism; D014961:X-Ray Diffraction
D019476:Insect Proteins; D010455:Peptides; D047011:Silk; D014867:Water; D005349:Fibroins; D000409:Alanine; D005998:Glycine