Study on noncovalent complexes of alkaloids with DNA duplex using electrospray ionization mass spectrometry

Screening and investigation of triplex DNA binders from Stephania tetrandra S. Moore by a combination of peak area-fading ultra high-performance liquid chromatography with orbitrap mass spectrometry and optical spectroscopies

The identification and screening of triplex DNA binders are important because these compounds, in many cases, are potential anticancer agents as well as promising drug candidates. Therefore, the ability to screen for these compounds in a high-throughput mode could dramatically improve the drug screening process. A method involving a combination of 96-well plate format and peak area-fading ultra high-performance liquid chromatography coupled with Orbitrap mass spectrometry was employed for screening bioactive compounds binding to the triplex DNA from the extracts of Stephania tetrandra S. Moore. Two compounds were screened out and identified as fangchinoline and tetrandrine based on the comparison of retention time and tandem mass spectrometry data with those of standards. The binding mechanisms of fangchinoline and tetrandrine at the molecular level were explored using tandem mass spectrometry, fluorescence spectroscopy, ultraviolet-visible spectroscopy, and circular dichroism. Collision-induced dissociation experiments showed that the complexes with fangchinoline and tetrandrine were dissociated by ligand elimination. According to these measurements, an intercalating binding is the most appropriate binding mode of these two alkaloids to the triplex DNA. The current work provides not only deep insight into alkaloid-triplex DNA complexes but also useful guidelines for the design of efficient anticancer agents.

Comparative study of the interactions between bisphenol analogues and serum albumins by electrospray mass spectrometry and fluorescence spectroscopy

RATIONALE

Bisphenol A and its alternatives are widely used in common consumer products and are known as environmental endocrine disrupting chemicals. Five bisphenol analogues, namely, tetrabromobisphenol A (TBBPA), tetrachlorobisphenol A (TCBPA), 4,4'-sulfonyldiphenol (BPS), bisphenol A (BPA) and 4,4'-hexafluoroisopropylidenediphenol (BPAF), were selected to study their interactions with serum albumins, aiming at a better understanding of the toxicological mechanisms of bisphenol compounds.

METHODS

The interactions between human and bovine serum albumins (HSA and BSA) with these five compounds were investigated by electrospray ionization mass spectrometry (ESI-MS). Fluorescence spectroscopy and molecular docking confirmed the ESI-MS observations and provided complementary information with respect to thermodynamic properties and binding modes.

RESULTS

TBBPA showed the highest binding ability with HSA and BSA, followed by TBBPA and BPS, whereas BPA and BPAF exhibited little or no binding with these serum albumins. The calculated thermodynamic parameters suggested that hydrogen bonds and electrostatic forces played important roles for these interactions. Binding energies of TBBPA, TCBPA, and BPS calculated by molecular docking were -35.18, -34.39, and -25.89 kJ mol(-1) , respectively, in good agreement with ESI-MS measurements.

CONCLUSIONS

The results of this study showed that halogenated substituents on the phenolic rings of bisphenol could enhance the binding ability with serum albumins. This work could provide useful information for further research on the relationship between molecular structures and toxicities of bisphenols. Copyright © 2016 John Wiley & Sons, Ltd.