Abstract: 【Objective】The objective of this study is to explore the changing pattern of protein component in the degummed silk fiber of silkworm (Bombyx mori), which will lay a foundation for understanding the distribution feature of silk proteins in the silk fiber, and will also provide references for improving silk processing technology.【Method】Sericins were removed from the silk fiber using various methods (including papain, sodium carbonate, urea, neural soap, and alkaline water). SDS-PAGE was used to detect the degumming degree and degumming effect on the fibroins by using different methods and different silk products. Silk proteins were extracted using LiSCN and then digested into peptides by using FASP method. Liquid chromatograph-tandem mass spectrometer was explored to identify the protein component in the degummed cocoon silk by using different methods and different silk products. The identified silk proteins were annotated by using bioinformatics. The abundances of silk proteins in different samples were compared by label-free quantitative method. 【Result】 Degumming of cocoon silk was performed by using five methods. Protein electrophoresis result showed that papain could degrade sericins to remove them from silk, but could not degrade the fibroins. Degummed by sodium carbonate caused slight degradation of sericins and serious degradation of fibroins, and degummed by neural soap and urea could strongly degrade both the sericins and fibroins, while degummed by alkaline water was not efficient. Proteomics research found that degummed silks by using papain and neural soap contained little sericins, but had fibroins, seroin 1 and glycine-rich protein. Degummed silk by using urea or sodium carbonate had fewest proteins when compared with the degummed silk by other methods, the major component of which were fibroins and the glycine-rich protein. Proteins in six silk products were detected by protein electrophoresis. The result showed that fibroins were relatively integrate in the raw silk and raw silk fabric, and partly degraded in the silk fabric, silk satin, and silk habotai, while serious degraded in the old silk clothes. The proteome analysis showed that raw silk and raw silk fabric mainly contained three fibroins, sericins 1, seroin 1, osiris 9a, glycine-rich protein and serine protease inhibitor SPI51, and silk fabric, silk satin, and silk habotai mainly had three fibroins and seroin 1, while old silk clothes mainly had three fibroins and the glycine-rich protein. 【Conclusion】 Degumming using papain could keep the maximum integrity of silk fiber, and degumming by sodium carbonate and urea are the best methods to removing sericins. Raw silk and raw silk fabric contain many sericins, and have integrated silk fiber. Silk fabric, silk satin, and silk habotai contain little sericins, and have partly-degraded silk fiber. After complete degumming, the silk still contain fibroin heavy chain, fibroin light chain, fibroin p25, seroin 1 and glycine-rich protein.

Key words: silkworm (Bombyx mori), silk, silk proteins, degumming, proteomics