The effect of metal ions on the conformation transition of silk fibroin

How the silkworm spins out such an excellent silk fiber has been a hot topic. The issue here is to;know how the coil chains in the gland of silkworm transform to beta -sheet in silk fiber. We used the regenerated silk fibroin to imitate the silk fibroin of the gland to investigate the effect of metal ion(Ca2+. Cu2+) on the silk spinning process of Bombyx mori silkworm. The solutions or gel obtained from hte mixture of regenerated silk fibroin and metal ions were dried for mimicking the gradual loss of water in the spinning process. The C-13 NMR spectrum simulation for C-beta nucleus of alanine quantitatively demonstrated that the conformation of the regenerated silk fibroin is dominantly of silk I, whereas the fibroin with metal ions has more silk II conformation. Raman spectroscopies show the consistent results with that of NMR. The binding of metal ion with carbonyl and amide in protein backbone allows the protein chain to array regularly, therefore leading to the beta -sheet formation.