NMR OF SILK FIBROIN .8. C-13 NMR ANALYSIS OF THE CONFORMATION AND THE CONFORMATIONAL TRANSITION OF PHILOSAMIA-CYNTHIA-RICINI SILK FIBROIN PROTEIN ON THE BASIS OF BIXON-SCHERAGA-LIFSON THEORY

The helicity of each residue for the sequence of the alanine residues in Philosamia cynthia ricini silk fibroin protein, where the number of the alanine residues were determined as 22, was calculated by using the Bixon-Scheraga-Lifson theory for the helix-coil transition of poly(L-alanine) including the hydrophobic side-chain interactions. The NMR line shape of the carbonyl carbon of the alanine residue observed in aqueous solution was simulated on the basis of the helicity of the alanine sequence determined here. In addition, the change in the NMR spectra of the alanine carbonyl region due to the temperature-induced helix-coil transition was also interpreted in terms of the change in the statistical weight parameter w, where w is related to the formation of an intramolecular hydrogen bond. From this theoretical analysis and CD observations, the structure of P. c. ricini silk fibroin in aqueous solution was clarified.