Folding process of silk fibroin induced by ferric and ferrous ions

L Bombyx mori silk fiber has useful mechanical properties largely due to a high content of ordered beta-sheet crystallites separated by non-crystal line spacers Metallic ions present in the silk dope in nature could affect the beta-sheet content in this work. we used solid-state C-13 NMR. EPR and Raman spectroscopy to investigate how the ferric/ferrous ions affect the folding process of the silk fibroin. NMR and Raman results indicate that ferric and ferrous ions have different effects on the secondary structure of silk fibroin. Ferric ions can induce a conformation change from helix to beta-sheet form in silk fibroin when their concentration exceeds a critical value, while ferrous ions cannot EPR results indicate that the ferric ions bound with silk fibroin have a high-spin state (S = 5/2) with g-value of g(1) = 1 950, g(2) = 1.990 and g(3) = 1 995. zero-field splitting interaction D of 1 2-2 cm(-1), and symmetric character of E/D - 1/3, resulting in an effective g-value of g' = 4 25. The hydrophilic spacer GTGSSGFGPYVAN(H)GGYSGYEYAWSSESDFGT in the heavy chain of silk fibroin is likely to be involved in the binding of ferric ions, and His, Asn and Tyr residues are considered as the potential binding sites (C) 2009 Elsevier B V All rights reserved