Solid-state 23Na NMR determination of the number and coordination of sodium cations bound to Oxytricha nova telomere repeat d(G 4T 4G 4)

Abstract

We report a solid-state 23Na NMR study of the bound sodium cations in a G-quadruplex formed by Oxytricha nova telomere DNA repeat, d(G 4T 4G 4) (Oxy-1.5). Using a 2D multiple-quantum magic-angle spinning 23Na NMR method, we observed three sodium cations residing inside the quadruplex channel of the Na + form of Oxy-1.5. Each of these sodium cations is sandwiched between two G-quartets. We found no evidence for sodium cations in the T 4 loop region. For comparison, solid-state 15N MAS NMR spectra were also obtained for the 15 NH 4 + form of Oxy-1.5. The insufficient resolution in the 15N MAS NMR spectra did not permit determination of the number of NH 4 + ions inside the quadruplex channel. The solid-state 23Na and 15N NMR spectra for Oxy-1.5 were also compared with those obtained for guanosine 5′-monophosphate.