Beta-turn Formation during the Conformation Transition in Silk Fibroin. Soft Matter, 2009, 5(14): 2777-2781-Xin (Terry) Chen

The changes of secondary structure of silk proteins, including b-sheet, helical and random coil content during the conformation transition process have been widely studied with various methods by many researchers, however few reports relate to b-turn formation. In this paper, b-turn formation during the conformation transition in both regenerated silk fibroin (RSF) solutions and films was monitored by time-resolved FTIR spectroscopy. The results show that the kinetics of b-turn formation varies not only in RSF solution or film, but also depends on the concentration of ethanol used to induce the conformation transition. Our observations confirm that the absorption band around 1690 cm^-1 is not the high frequency band of anti-parallel b-sheet, but represents b-turns possibly together with a component derived directly from b-sheet as proposed in our previous work. Our findings also suggest that the free adjustment of silk fibroin macromolecular chains is very important for the formation of regular b-sheet structure, essential for the strength of silk fibers, with important implications for the natural spinning mechanism of animal silks and attempts to copy this industrially.

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