Comparative Studies On Interaction Mechanism Of Triterpenoids From Momordica Charantia With Proteins

Triterpenoids are an important class of natural drugs,which are widely used and have many biological activities such as antiviral,antitumor,and anti-inflammatory.Protein is not only the carrier of drug molecules but also their target.Small molecules entering the body must first bind to the carrier protein and then act with the targeted molecules to exert their drug effects.At present,it is difficult to directly determine the binding of small drug molecules to proteins in vivo.Therefore,the determination of the binding of small drug molecules to proteins is often carried out in vitro under simulated physiological conditions.In this thesis,the interactions of triterpenoid compounds T1 and T2 with human serum albumin(HSA)and porcine pancreatic ?-amylase(PPA)were studied by ultraviolet-visible absorption spectroscopy,fluorescence spectroscopy,synchronous fluorescence spectroscopy,circular dichroism and molecular docking,respectively.The interaction information between the two small molecules and the proteins were obtained,which include fluorescence quenching type,binding parameter,thermodynamic parameter,type of binding force,binding distance,binding position and protein conformation change.The mechanisms of the interactions between small molecules and proteins were expounded at the molecular level.The main contents of this thesis are as follows:Firstly,the structures and functions of triterpenoid compounds T1 and T2,human serum albumin and porcine pancreatic ?-amylase were introduced.The commonly used research methods and the main research contents of the interactions between small drug molecules and proteins were discussed.And the significance of this study was proposed.Secondly,the interactions of the two triterpenoid compounds T1 and T2 with human serum albumin(HSA)under simulated physiological condition were studied by using ultravioletvisible absorption spectroscopy,fluorescence spectroscopy,synchronous fluorescence spectroscopy,and circular dichroism combined with molecular docking techniques.The experimental results showed that T1 and T2 can induce endogenous fluorescence quenching of HSA,the quenching types are static quenching and combined quenching,respectively.The binding distances of T1 and T2 to HSA are 3.94 nm and 3.34 nm,respectively.Both T1 and T2 are bound to the Sudlow site I of HSA.Hydrogen bonds and van der Waals forces play important roles in the stability of the T1-HSA complex,and hydrophobic interactions play a major role in the binding of T2 to HSA.In addition,the conformation of HSA was changed by the combination with T1 and T2.Finally,the interactions of the two triterpenoid compounds T1 and T2 with porcine pancreatic ?-amylase(PPA)were studied by multispectral method and molecular docking technique under simulated physiological condition.The results obtained indicated that the endogenous fluorescence of PPA can be quenched by T1 and T2,and both the quenching types are combined quenching.The PPA binding strength of T2 was higher than that of T1.The binding distances of T1 and T2 to PPA are 2.69 nm and 2.87 nm,respectively.The binding sites of T1 and T2 on PPA are all close to the active site of PPA.Hydrogen bonds and van der Waals forces play important roles in the stability of the T1-PPA and T2-PPA complexes.In addition,the conformation of PPA was changed after combined with T1 and T2.This study should be helpful to the understanding of the transportation,metabolism and distribution process of triterpenoid compounds T1 and T2 in vivo as well as the design and development of the relative new drugs.