Polyphenol-mediated Protein Aggregation And Applications Of Amyloid Fibrils

The present work is concerned with protein aggration and amyloid fibrillation.We concentrate on studying the inhibition of natural polyphenols on protein amyloidfibrillation experimentally and theoretically, which can lead to a better understandingof the polyphenol-regulated mechanism during this process and to give a possiblegeneral mechanism. We try to explore the application of protein aggregation and itsproduct amyloid fibrils on protein drug delivery and material functionalization.First of all, we focused on the effects of different polyphenol compounds on thekinetics of insulin aggregation, as well as the structure and morphology of insulinaggregates using various biophysical technologies. Oligomeric polyphenolcompounds showed potent inhibition at all stages of insulin fibrillation and redirectinsulin aggregation pathway via the formation of unstructured, off-pathwayaggregates. The results suggested that the antioxidative activity, chemical structure,and protein inherent properties were key factors on the anti-amyloidogenic activity ofpolyphenol.Secondly, insulin amyloid fibrils were disaggregated by laser irradiation coupledwith small aromatic molecules. We investigated the inhibition mechanism by acombination of steady-state/time-resolved fluorescence spectroscopy, DFT calculation,and molecular docking. The results suggested that the nature of disaggregation was todisrupt hydrophobic interactions between insulin amyloid fibrils. Destruction ofamyloid fibrils would occur when small molecules could bind to insulin fibrilsefficiently and change the hydrophobic environment surrounding amyloid fibrils.Thirdly, natural oligomeric procyanidin (OPC) with high pharmacological andbiological activities was successfully used to synthesize OPC–insulin (OPC–INS)nanoparticles with different aggregation sizes for sustained and controlled delivery ofhydrophilic insulin. The aggregation size of OPC–INS nanoparticles was regulated byOPC concentration, pH value, and incubation time. The optimal condition was thatinsulin incubated with100μM OPC for6h in pH7PBS buffer. In the self-assemblyof insulin, OPC could serve both in the encompassing of insulin aggregates as astabilizer and cross-linking different amounts of insulin aggregates into OPC–INS nanoparticles as interphase. In the best case for OPC–INS nanoparticles, only~21%of insulin was released in37d. This study showed that the OPC–INS nanosystem ispromising to serve as a long-acting insulin release formulation, and OPC has greatpotential as a drug carrier for nanomedicine.Fourthly, we utilized the aggregation of β-LG to form β-LGA-coated AuNPsnanochains for drug delivery of tea polyphenol (TPP). The length ofAuNPs/β-LGA/TPP nanochains was regulated by TPP concentration, aggregationtime and pH value. The optimal condition was TPP of10μM in pH7PBS for30minof incubation time, under which condition we obtained AuNPs/β-LGA/TPP consisted3─5AuNPs. This nanochain could benefit from the protection effect of β-LGA onTPP antioxidant activity and the potential detection application of AuNPs.Furthermore, the nanochains have also shown ThT fluorescence response intensity.Lastly, the β-LGA/GO nanofibrils and its thin film were prepared by usingβ-LGA amyloid fibrils as templates via electrostatic and hydrophobic interaction. Themorphology of β-LGA/GO nanofibrils was regulated by pH value and the volumeratio of GO to β-LGA. The optimal condition was pH4.6with the GO/β-LGA ratio of30:1, under which condition β-LGA/GO nanofibrils had a diameter of20─50nm. Theresults suggested that β-LGA/GO thin film has a better capacitance and hydrophilicproperties, facilitating its application in the filed of cell culture.