On the affinity and specificity of quercetin for DNA

The potential of quercetin (QUE), being a member of the whole family of structurally different flavonoids, to serve as an anti-tumor agent has been recognized, but not fully understood. The interactions between DNA and a series of the flavonoids have so far been mainly investigated using a variety of experimental techniques. Herein, the specificity of QUE for DNA is explored using sophisticated density functional theory (DFT) methods employed to generate the optimized structure of QUE in complex with adenine (A), guanine (G), thymine (T) and cytosine (C), respectively. As far as a preference of QUE is concerned, structural and energetic as well as NMR chemical shift arguments clearly indicate a highest for G and a lowest for C. This observation is further substantiated by analyzing the binding modes of QUE docked in a quadruplex receptor structure of DNA and in a duplex receptor structure of DNA. Among all possible single point mutations of the DNA quadruplex and duplex residues, several critical ones causing a conspicuous stabilizing effect on the original complexes of QUE with the DNA receptors are identified. Consequently, several fundamental standpoints shedding new light on the molecular mechanisms underlying the interactions between QUE and DNA are discussed.