Effects Of Small-molecule Compound On Protein Aggregation Process

The aggregation and deposition of the amyloid protein can cause lots of diseases.Many small molecules have been found to facilitate or inhibit the aggregation of amyloid protein.However,their functional mechanisms are still unknown,which hindered the development of aggregation inhibitors.Herein,?-amyloid protein(A?),Thioflavine T(ThT)and(-)Epigallocatechin gallate(EGCG)were chosen to explore the working mechanism of small molecules on the aggregation of amyloid protein.This work will promote the development of amyloid protein aggregation theories and benefit in the design of novel inhibitors.Firstly,the effect of ThT on the aggregation of A?40 was studied.The fluorescence kinetic assays showed that,ThT accelerated the A?40aggregation at low ThT concentration,while at high ThT concentration;the accelerating effect will be suppressed.Isothermal titration experiment showed that hydrophobic and electrostatic interaction contributed a lot to the weak binding of ThT onto A?40 monomer.Further experimental results from circular dichroism,transmission electron microscope and seeded assays showed that the interaction between ThT and A?40 is too week to change the secondary structure,morphological structure and surface properties of the final-formed fibrils.In other words,Th T can only affect the primary nucleation of A?40 but failed to change the secondary nucleation and structure of fibrils.In the study of EGCG affecting the aggregation of A?40,similar results were found.Though EGCG was reported to be an effective inhibitor,it accelerated the aggregation of A?40 at low EGCG concentration.The interaction between EGCG and A?40 monomers was attributed to hydrogen bond and hydrophobic interaction,which was stronger than that between ThT and A?40 monomers.Besides,EGCG could slow down the secondary structure transition of A?40.Moreover,with increasing EGCG concentration,the cross-link degree of A?40 fibrils decreased,and fibrils gradually transfer to spherical oligomers.Especially,EGCG inhibited the secondary nucleation of A?40 dramatically.Therefore,though EGCG of low concentration accelerated the aggregation of A?40,it could change the structure and surface properties of A? fibrils by remodeling mechanism and finally inhibit the secondary nucleation.