Spectroscopic Study On The Interactions Of Three Alkaloids With G-quadruplex

Tumor is a serious common and frequently-occurring disease,which could cause human deaths.It is one of the most difficult disease to treat and the most expensive to invest.Studies have shown that the ligands that could facilitate the formation and stabilization of G-quadruplex structure can inhibit telomerase activity or lower cancer gene transcription and inhibitate tumor.Hence,studies of the interactions of G-quadruplex and ligands have become one of hot studies on tumor treating and investing.Alkaloids,as one important class of natural compounds,have significant biological activities.Protoberberine alkaloids are isoquinoline alkaloid and the most representative compounds are berberine,jatrorrhizine and palmatine with antibacterial,analgesic and hypoglycemic effects.Recent studies have shown that berberine is likely to play an important role in the treatment of cancer and AIDS.In this thesis,we studied the interactions between three protoberberine alkaloids(berberine,jatrorrhizine,palmatine)and G-quadruplex(formed by PS2.M),and obtained the binding mode ? the binding constant and other useful information.Chapter 1,we introduced the structure of G-Quadruplex and its biological significance,then introduced some of the potetial ligands that can bind with G-Quadruplex and their binding modes;Again,listed the research methods of small molecular ligands and G-Quadruplex;finally,illustrated the content and significance of this thesis.Chapter 2.The characteristic spectra of G-quadruplex were characterized by NMR and CD,meanwhile the interaction spectra between jatrorrhizine and G-quadruplex were studied by fluorescence spectrum,ultraviolet absorption spectrum and nuclear magnetic resonance,which show the strong interaction of jatrorrhizine with the G-quadruplex.With the addition of G-quadruplex,the fluorescence spectra show that the fluorescence intensity of jatrorrhizine appeared significant increase in530 nm,and UV spectra show the phenomenon of hypochromic effect and red shift.Jatrorrhizine has strong binding ability with DNA.According to the continuous equivalent change method,it is inferred that the jatrorrhizine and DNA are combined with 1:1.And according to the Scatchard equation,it is calculated that binding constant is 3.12×106 L/mol and the binding site is 0.98.The experiments indicate that jatrorrhizine has strong binding capacity with G-quadruplex DNA and may combined with DNA by terminal stacking.Chapter 3.The characteristic spectra of G-quadruplex were characterized by NMR and CD,meanwhile the interaction spectra between palmatine and G-quadruplex were studied by fluorescence spectrum,ultraviolet absorption spectrum and nuclear magnetic resonance,which show the strong interaction of palmatine with the G-quadruplex.With the addition of G-quadruplex,the fluorescence spectra show that the fluorescence intensity of palmatine appeared significant increase in 530 nm,and UV spectra showed the phenomenon of hypochromic effect and red shift.Palmatine has strong binding ability with DNA,and the binding mode is intercalation or terminal stracking.According to the continuous equivalent change method,it is inferred that the palmatine and DNA are combined with1:1.And according to the Scatchard equation,it is calculated that binding constant is 4.83×106 L/mol and the binding site is 0.75.The experiments indicate that palmatine has strong binding capacity with G-quadruplex DNA.Experiment on the inhibition of peroxidase activity of G-quadruplex/Hemin complex shows that the interaction mode between palmatine and Gquadruplex is terminal stracking.Chapter 4.This chapter we use UV,fluorescence spectrum and CD spectrum studied the selective interactions between berberine and two kinds of intermolecular G-quadruplex and one intramolecular G-quadruplex.Then we discussed their binding modes.Three kinds of DNA can cause UV absorption spectra of berberine appeared different degrees of red shift and hypochromicity.It showed that berberine can interact with G-quadruplexDNA;At the same time,the fluorescence intensity of berberine intermolecular G-quadruplex was enhanced obviously higher than that of intramolecular G-quadruplex with the adding of G-quadruplex.Job's plot and Scatchard equation results showed that berberine and DNA are combined with 1:1.The binding constants of two kinds of intermolecular G-quadruplex DNA(106 L/mol)with berberine was significantly higher than that with intramolecular G-quadruplex(105L/mol).In addition,all experiments datas were compared with duplex DNA.The results showed that berberine can combined with the two kinds of intermolecular G-quadruplexes at low concentration(micromolar orders),while duplex DNA hardly interact with berberine at this condition.The berberine has higher selectivity to G-quadruplex.We hope these conclusions could be useful for the design of those anticancer drugs based on G-quadruplex.