Investigation of Interaction of Isoquinoline Alkaloids with Guanine-Guanine-Adenine Triplex DNA by Mass Spectrometry and Spectroscopy
The interaction of several small-molecule alkaloids,namely coptisine,jateorhizine,epiberberine,berberrubine,columbamine,fangchinoline and tetrandrine,with guanine-guanine-adenine(GGA)triplex DNA was investigated by mass spectrometry(MS),ultraviolet-visible(UV-vis)spectroscopy,fluorescence spectroscopy,and circular dichroism(CD)spectroscopy.The effect of the 7 kinds of metal ions on the stability of GGA triplex DNA was investigated by direct infusion electrospray ionization mass spectrometry(ESI-MS),and the binding degree was highest when Ni2+was employed.Among the 7 kinds of alkaloids,tetrandrine had the highest affinity to the GGA triplex.All the data unequivocally accommodated diverse mechanisms for interaction between the isoquinoline alkaloids and the GGA DNA triplexes.At least,electrostatic attraction and intercalative-binding modes were observed in the study.Interestingly,UV melting denaturation assay revealed that the two isoquinoline alkaloids including columbamine and berberrubine enhanced the stability of the GGA triplex structure.The UV-melting curve profile could not accurately determine the stabilizing effect of small molecules on the structure of GGA triplex DNA.Further detection by UV-vis spectroscopy showed that epiberberine could stabilize the structure of GGA triplex DNA,but other small molecules couldn't stabilize the structure of GGA triplex DNA.The mode of interaction was further investigated,and firstly,fluorescence spectroscopy was applied to construct the ethidium bromide(EB)-GGA triplex DNA system,and then the reactions of small molecule alkaloids at different concentrations with EB-GGA triplex DNA system were studied.And it was found that epiberberine,fangchinoline and tetrandrine small molecules could replace the EB and insert to bind GGA triplex DNA.Finally,the circular dichroism spectroscopy was used to investigate the binding mode,and the negative CD signal was found.The investigation provided new insights into the interaction of isoquinoline alkaloids with GGA triplex DNA.
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