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

Abstract

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 13C solution NMR spectra of Anaphe silk fibroin and several model peptides with Ala and Gly residues indicates that (AAG)n1 and (AG)n2 are the main sequences. In addition this analysis also indicates that the sequence contains (A)m (where m > 2) such as (AAAG)n3, (AAGAG)n4, and (AAAGAG)n5. GG sequences were absent at a level that could be detected by our NMR method. The 13C CP/MAS NMR study shows that the fiber structure is heterogeneous, but predominantly β-sheet structure and the length of (AG)n2 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.