Heat-induced Self-assembly Fibrils From Soybean Glubulins And Control By Electrostatic Screening

How to utilize the soybean protein more efficiently and expand its industrial applicationshas become an urgent science and technology problem to solve. The aim of this thesis is toprepare and characterize the self-assembly aggregation of 7S globulin and 11S globulin andexplore the underlying mechanism, which might act as the theoretical basis to widen thesoybean resources, moreover, we studied the influences of ionic strength on self-assemblyfibrils, expecting to control the formation of fibrils. The main research results are as follows:The viscosity of 7S globulin and 11S globulin was increasing when heated for differenttime. The building blocks formed at the initial heating periods(e.g. <0.5 h) according to Th Tfluorescence data. Longer heating period might be beneficial for these initially formedbuilding blocks or fibrils. Congo red suggested the formation of amyloid-fibril after heatingfor certain time, however the trend varied among different samples. Far-UV CD indicated thatthe change extent of elliplicity of 7S globulin was more drastic than 11S globulin. AFMshowed that 7S globulin, 11S globulin and their mixture(1:1, w/w) formed fibrils after heatingat 80℃for 12 h, but the structural characteristics were different. SDS-PAGE suggested that7S globulin could hydrolyze more easily than 11S globulin. It might be due to the largercontent of total charged amino acids in 7S globulin, which made polypeptides hydrolysis andconformation changes easier. The differences of hydrolysis and conformation changesdetermined the ability to form self-assembly fibril aggregation.The dynamic light scattering was employed to characterize the particle size during theformation of self-assembly aggregation. Both the size distribution of 7S globulin and 11Sglobulin shifted to larger diameter. Yet the two globulins presented different tendencies as tothe mean particle size: heating samples of 7S globulin with lower ionic strength(0-200 mM)resulted in gradual decreases in mean particle diameter, and after then, the diameter sizeprogressively increased with the heating time, while samples with higher ionic strength keptrising; the mean diameter of 11S globulin continued increasing with the heating timeregardless of the ionic strength. Th T fluorescence indicated that increment of ionic or protein concentration could accelerate the growth of building units. Far-UV CD indicated that thesecond conformation changes of 7S glubulins with different ionic strength were similar afterheating for different periods of time, and the elliplicity at 215 nm was well in agreement withTh T fluorescence data among the samples with ionic strength 0-100 mM, but inconsistentwhen increasing the ionic strength to 200-300 mM. Moreover, the change extent of elliplicityof 7S globulin was more drastic than 11S globulin. The elliplicity at 280 nm of 7S globulinschanged severely, and had a positive relation with ionic strength. AFM could provide thedetailed morphology of self-assembly fibril and prove the enhancement function of ionicstrength and protein concentration. In terms of SDS-PAGE, ionic strength had little effects onthe peptides hydrolysis of both 7S globulin and 11S globulin. Thus, the self-assembly fibrilsaggregation depended mainly on the repulsion and attraction between protein molecular.