G-quadruplex formation and sequence effect on the assembly of G-rich oligonucleotides induced by Pb²⁺ ions

The lead-induced folding into G-quadruplex structures for three guanine-rich oligonucleotides, two model human telomeric oligomers (HTG/T2) and thrombin-binding aptamer (TBA), was characterized by equilibrium titrations, rapid mixing techniques and stopped-flow kinetics. The analysis of optical titration data reveals that the saturated Pb²⁺-DNA binding stoichiometries are 1:1, 2:1 and 3:1 for TBA, HTG and T2, respectively. Thermal denaturation experiments were performed to determine the structural stability. The overall results are consistent with the higher stability of T2 that contains four G-quartets, as opposed to HTG and TBA that have only three and two quartets, respectively. We also present kinetic studies of the formation of G-quadruplexes of G-rich DNA induced by Pb²⁺ ions. The binding of Pb²⁺ ions to G-DNA is a complex multiple pathway process, which is affected by the sequence of the G-DNA. The studies show that the connecting loops of the DNA play an important role in modulating the structures. © The Royal Society of Chemistry.