Structural Analyses of Anaphe Silk Fibroin and Several Model Peptides Using 13C NMR and X-ray Diffraction Methods

The Thaumetopoeid silkmoth Anaphe reticulata is highly abundant in equatorial and southern Africa and a potential commercial source of silk. In this paper, we report detailed structural characteristics of the silk fibroins. Comparison of the 13 C solution NMR spectra of Anaphe silk fibroin and several model peptides with Ala and Gly residues indicates that (AAG)n 1 and (AG)n 2 are the main sequences. In addition this analysis also indicates that the sequence contains (A) m (where m > 2) such as (AAAG)n 3, (AAGAG)n 4, and (AAAGAG)n 5 . GG sequences were absent at a level that could be detected by our NMR method. The 13 C CP/MAS NMR study shows that the fiber structure is heterogeneous, but predominantly β-sheet structure and the length of (AG)n 2 is too short to form the Silk I structure detected in Bombyx mori silk fibroin. X-ray diffraction analyses gave information on the higher order structure and hydrogen-bonding character of Anaphe silk fiber.