Conformational Transition Of Natural Spider Silk Protein

Spider dragline silk, owing to its excellent mechanical properties, has receivedresearchers’ attention since the70s. In the90s of20thcentury, the study of spider silk got tothe climax. However, the limited yield of spider silk fibers and the poor properties ofregenerated or recombinant spider silk fibers compared to natural spider silk restrict thedevelopment of artificial spider silk. Ornithoctonus huwena is a kind of spider that can bebred artificially and its spun silk fibers have good potential application value in biomedicalareas.In this paper, we chose Ornithoctonus huwena spider silk as object to investigate theeffect of solvents on the amino acid composition, molecular weight distribution andmolecular conformation of regenerated spider silk protein respectively using amino acidanalyzer, SDS gel electrophoresis and circular dichroism (CD) analysis. On this basis, byCD and atomic force microscopy, the molecular conformational transition andself-assembly of regenerated spider silk protein aqueous solution were studied. The resultsshowed as followed:(1) Relationship between solvents and amino acid composition of regeneratedOrnithoctonus huwena spider silk In the regenerated spider silk protein prepared by thethree solution systems, alanine, serine and glycine still remained the leading positionconsistent with the native spider silk, except the decreased content of alanine. In theregenerated spider silk protein aqueous solution prepared from LiBr, the content of glycinehad a substantial growth and in the spider silk protein/HFIP solution, the contents oftyrosine and valine increased.(2) Relationship between solvents and molecular weight distribution ofregenerated Ornithoctonus huwena spider silk The spider silk protein in HFIP had anarrower molecular weight distribution and a much higher molecular weight compared tothat in aqueous solution prepared from LiBr. (3) Relationship between solvents and molecular conformation of regeneratedOrnithoctonus huwena spider silk The silk protein in HFIP had a main conformation of-helix and in the silk protein aqueous solution, there was also a certain proportion of-sheet structure.(4) Effect of environmental conditions on the molecular conformationaltransition of regenerated Ornithoctonus huwena spider silk protein aqueous solutionTime and temperature had little effect on the conformation of regenerated spider silkprotein aqueous solution; With the increase of concentration, the conformation of silkprotein had a trend of transition from-helix to-sheet structure; No matter increasing ordecreasing the pH value of original silk protein solution (pH=6.71), the conformation ofspider silk protein both can transform form-sheet to-helix or random coil structures,however, when pH increased to8.54, the content of-sheet structure was dominant;Relative to Na+, K+had a larger impact on the conformation of spider silk protein,improving the formation of-sheet structure.(5) Effect of environmental conditions on the self-assembly of regeneratedOrnithoctonus huwena spider silk protein aqueous solution With increasing time, themicrostructure of spider silk protein changed from nanoparticles to aggregation ofnanoparticles, to nanofilaments, finally to aggregation of nanofilaments; The increasingconcentration lengthened the nanofilaments and caused the aggregation; When pH was6.11, the uniform nanofilaments appeared; K+can induce the formation of nanofilamentsand minish the diameters of nanofilaments and nanoparticles, meanwhile, it can contributeto the formation of hierarchical microstructure of spider silk protein.