Abstract: The conformation transition of silk fibroin in the silk glands of Bombyx mori was studied by scanning tunneling microscopy. The dilute aqueous solution of fibroin synthesized in the posterior glands is in a form of random coils,which are transformed into coiled-coil and later into individual α-helices in the middle glands.During spinning,they turned into β-strands and finally to β-sheets,The formation of liquid crystalline state aids the process of spinning.The STMimages were taken dozens of time for each sample at different spots,which can represent the general nature of fibroin in the glands of silkworm.So far as we know,this is the first time to have the individual fibroin,or more specifically,the α-helix and β-sheet structure of protein,to be imaged.

Key words: Silk fibroin, Conformation transition, Scanning tunneling microscopy