Reevaluation of the stability of G-quadruplex structures under crowding conditions.

To evaluate the stability of G-quadruplex structures comprehensively, parallel (type I), antiparallel (type II), and hybrid (type III) G-quadruplexes in the presence of monovalent and divalent cations were assessed by UV-melting technique under dilute and crowded conditions. In the presence of monovalent cations, the stability of G-quadruplexes was increased by the presence of molecular crowding agents. Surprisingly, crowding agents stabilized parallel G-quadruplex, but had no effect on stability or destabilized antiparallel or hybrid G-quadruplex structures in the presence of divalent cations. A hydration study of the antiparallel G-quadruplex revealed that more water molecules are bound in the presence of divalent cations than with monovalent ions. These analyses under conditions that mimic those in cells further our understanding of how G-quadruplex structures are involved in biological processes.