Interaction Studies Of Serum Albumin With Polyphenolic Compounds Under Simulated Physiological Environment And Its Effect On Protein Properties

Polyphenolic compounds are secondary metabolites widely discovered in the world and have the function of anti-tumor,antibacterial and anti-oxidation physiological.Serum albumin,makes up the largest proportion of proteins in plasma,has the function of transporting and transporting compounds.After entering the human body,the polyphenolic compound first binds to human serum albumin in the circulatory system and then comes to various other parts of the body to be distributed and absorbed.Therefore,the study of the interaction between polyphenolic compounds and serum albumin can achieve the control of the concentration,effect and action time of polyphenolic compounds,which is of great significance for ensuring curative effect and rational use of drugs.At present,the research on the interaction between compound and protein is carried out in a dilute solution environment in vitro,but the real environment in the living body is extremely crowded,so the conclusions obtained in the dilute solution will be different from the actual situation.In addition,the combination of polyphenolic compounds and proteins not only affects the pharmacodynamics,pharmacokinetics and other properties of the compounds,but also affects the structure and properties of the proteins.Therefore,the study of the interaction process is of great significance for understanding the relationship between protein structure and function.Various biophysical and computer simulation methods were used to study the interactions between brazilin,hematoxylin,hematein and human serum albumin,to explore the effects of crowded environment on their binding,and to analyze the relationship between the structure and binding affinity of polyphenolic compounds and the effects on protein properties（antioxidative damage and anti-aggregation）,the following research contents were carried out:1.Under physiological p H conditions:Brazilin,hematoxylin and hematein quenched the fluorescence of HSA by a static quenching and non-radiative energy transfer mechanism.The binding site was located in the hydrophobic cavity of protein subdomain IIA,and the binding strength was moderate.Bra and Hto had stronger binding affinity than Hte.The main binding forces of Bra and Hto to HSA were hydrogen bond and van der Waals force.The binding of Hte to HSA was mainly hydrophobic interaction forces.Furthermore,polyphenolic compounds binding to HSA led to the structural alteration of HSA.In addition,computer simulation was used to study the binding mode of polyphenol compounds and the kinetic behavior of the complexes.The results were found to be consistent with the experimental tests.Finally,the oxidative damage test of HSA showed that polyphenolic compounds could inhibit the oxidative damage of HSA,but Bra and Hto had stronger inhibition ability than Hte.The difference in the structure of polyphenolic compounds（different hydroxyl and double bonds）not only had effect on their abilities to bind HSA,but also affected their abilities to inhibit HSA oxidative damage.2.In a crowded condition:We examined the effects of different crowding agents on human serum albumin structure and found that 100 g L^-1 PEG 2000 and PEG 4000had the least impact.Therefore,these two crowding reagents were selected to simulate the crowded environment in the living body.It was found that the quenching mechanism,and binding mode of polyphenolic compounds on HSA were not affected by the crowded environment,and the same as the dilute solution environment,and the binding also caused the conformation of the protein to change.Polyphenolic compounds in crowded environment could inhibit the aggregation of HSA,but the inhibitory effect was not as pronounced in dilute solution environment,which may be related to excessive viscosity in crowded environments.At the same time,the inhibition effect of Hte in the three polyphenol compounds was the worst.In summary,the polyphenolic compounds’ability to bind HSA their ability to inhibit protein aggregation were not only related to the structure of the compounds,but also to the crowded environment.