Complicated behavior of G-quadruplexes and evaluating G-quadruplexes' ligands in various systems mimicking cellular circumstance

• Cell-free system was constructed using HL60 cell extract.
• Topologies and stability of G-quadruplexes were identified in different systems.
• G-quadruplex’s ligands’ effects were evaluated in different systems.

Environments surrounding G-rich sequences remarkably affect the conformations of these structures. A proper evaluation system mimicking the crowded environment in a cell with macromolecules should be developed to perform structural and functional studies on G-quadruplexes. In this study, the topology and stability of a G-quadruplex formed by human telomeric repeat sequences were investigated in a macromolecule-crowded environment created by polyethylene glycol 200 (PEG200), tumor cell extract, and Xenopus laevis egg extract. The interactions between small molecules and telomeric G-quadruplexes were also evaluated in the different systems. The results suggested that the actual behavior of G-quadruplex structures in cells extract is quite different from that in the PEG crowding system, and proteins or other factors in extracts might play a very important role in G-quadruplex structures.