NMR Characterization of Silk Proteins

Structures of Bombyx mori silk fibroin have been studied in solution, in silkworm and in the solid state by means of solution and solid 13C and 15N NMR spectroscopies. The silk fibroin yields very sharp 13C NMR signals in aqueous solution and in silkworm, indicating the fast segmental motion of the main chain in spite of a fairly high molecular weight, 3 x 105. This makes detailed sequential and conformational analyses of the silk fibroin possible. The structure of the silk fiber in the solid state was studied with 15N CP NMR and 15N isotope-labeled silk fibroins on the basis of the chemical shift tensors in detail. The torsion angles of the glycine, alanine and tyrosine residues were determined.