2akg
From Proteopedia
Thallium form of the G-Quadruplex from Oxytricha Nova, d(G4T4G4)2
Overview
Monovalent cations play an important role in many biological functions. The guanine rich sequence, d(G4T4G4), requires monovalent cations for formation of the G-quadruplex, d(G4T4G4)2. This requirement can be satisfied by thallium (Tl+), a potassium (K+) surrogate. To verify that the structure of d(G4T4G4)2 in the presence of Tl+ is similar to the K+-form of the G-quadruplex, the solution structure of the Tl+-form of d(G4T4G4)2 was determined. The 10 lowest energy structures have an all atom RMSD of 0.76 +/- 0.16 A. Comparison of this structure to the identical G-quadruplex formed in the presence of K+ validates the isomorphous nature of Tl+ and K+. Using a 1H-205Tl spin-echo difference experiment we show that, in the Tl+-form of d(G4T4G4)2, small scalar couplings (<1 Hz) exist between 205Tl and protons in the G-quadruplex. These data comprise the first 1H-205Tl scalar couplings observed in a biological system and have the potential to provide important constraints for structure determination. These experiments can be applied to any system in which the substituted Tl+ cations are in slow exchange with the bulk ions in solution.
About this Structure
Full crystallographic information is available from OCA.
Reference
205Tl NMR methods for the characterization of monovalent cation binding to nucleic acids., Gill ML, Strobel SA, Loria JP, J Am Chem Soc. 2005 Nov 30;127(47):16723-32. PMID:16305263 Page seeded by OCA on Sat May 3 19:09:29 2008
