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2akg
From Proteopedia
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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
2AKG is a Protein complex structure of sequences from [1]. 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
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