6SX6:
reference: GC ends control topology of DNA G-quadruplexes and their cation-dependent assembly., Pavc D, Wang B, Spindler L, Drevensek-Olenik I, Plavec J, Sket P, Nucleic Acids Res. 2020 Mar 18;48(5):2749-2761. doi: 10.1093/nar/gkaa058. PMID: 31996902

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).