Study On The Separation,Assembly And Aggregation Of Silk Fibroin Polypeptide Chains

Silk fibroin consists of H chain,L chain and P25 chain,but the structure and performance of these peptide chains are lack of in-depth study.In this paper,it is expected to isolate the peptide chain of silk fibroin,analyze the peptide structure of silk fibroin to understand the structure of silk fibroin,and expand the application of silk fibroin in biomaterials.From the point of view of the disulfide bond between the broken H chain and the L chain and the sulfhydryl protection under reducing environmental conditions,high molecular weight silk fibroin(HSF)and low molecular weight silk fibroin(LSF)were obtained by using different dialysis bags to intercept the protein of interest.The SDS-PAGE shows that the molecular weight of HSF is above 80kDa and contains a large amount of H chain,which is similar in amino acid composition to H chain.LSF has a molecular weight of about 10 to 30 kDa,and the amino acid composition is similar to the L chain,but contains some H chain.The silk fibroin(SF)solution is difficult to effectively collide and aggregate between the silk fibroin colloidal particles under the protection of the hydration layer composed of hydrophilic groups,so that the solution state can be maintained for a long time.High molecular weight silk fibroin(HSF),with high surface activity,can reduce the surface tension of water to 20mN/m,has strong hydrophobicity,is unstable in aqueous solution,and is easy to assemble into a certain micro-nano structure.SEM showed that nanofiber structure could be formed at low concentration(5mg/mL)and low temperature(37?).At the high temperature and high concentration,accompanied by the formation of nanofiber structure,simultaneous appearance slice structure.HSF forms a rod-shaped micelle structure in a highly polar environment;a star-shaped grid structure is formed in a weakly polar environment.When the environment pH of the HSF solution is 6,the micelle bead and the folded crank sheet structure are formed.But when the pH is 8,a ring-like structure and a ring-shaped fibrous structure are formed.In the process of HSF transition from colloidal particles to nanofibers,it is accompanied by the transformation of molecular conformation from random coil to p-sheet.The low molecular weight silk fibroin(LSF)obtained from the double layer dialysis intermediate layer solution has a short molecular chain segment and the initial morphology tends to the state of the spherical colloidal aggregate.SEM shows that it is easy to form a three-dimensional space grid structure under high concentration(5mg/mL)conditions.At low concentrations(2.5mg/mL,5mg/mL),molecules are more likely to aggregate due to the inhibition of hydrophilic groups.The relationship between self-assembly and temperature is similar to concentration,molecules tend to aggregate at low temperatures;At high temperatures,the molecules are more easily ordered and arranged,and an annular sheet structure appears.During the assembly process,the LSF changes with the microstructure of the microstructure,but the molecular conformation still exists in the form of random.