Characterization of potassium binding with human telomeres

Human telomeres are G-rich tandem repeats that assume G-quadruplex structures at the ends of chromosomes. Stabilization of telomeric G-quadruplex represents a significant drug target for inhibiting the telomerase activity that is required in about 85% of cancers. Metal ions have been revealed as important stabilizers to DNA G-quadruplexes, but their binding process with human telomeric G-quadruplex remains unclear. In this report, we show that K+ traverses into the G-tetrads centre of two G-tetrad layers through the half-capped top pathway constructed by the two edge-wise loop bases. The binding is mediated by the electrostatic interactions between K+ and the nearby bases of G-tetrads. However, direct traverse of K+ into the interior of G-quadruplex is negatively regulated by the steric hindrance of water molecules. Once K+ enters the G-quadruplex, stabilization of the in-plane or sandwiched conformation of the telomeric G-quadruplex K+ complex is maintained by surrounding water molecules. These findings provide insights into the atomic interactions between K+ and telomere G-tetrads for targeted drug design.