'''NMR Structural Analysis of the dimer of 5MCCTCATCC'''
===NMR Structural Analysis of the dimer of 5MCCTCATCC===
==Overview==
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At slightly acidic pH, the association of two d(5mCCTCACTCC) strands results in the formation of an i-motif dimer. Using NMR methods, we investigated the structure of [d(5mCCTCACTCC)]2, the internal motion of the base pairs stacked in the i-motif core, the dimer formation and dissociation kinetics versus pH. The excellent resolution of the 1H and 31P spectra provided the determination of dihedral angles, which together with a large set of distance restraints, improve substantially the definition of the sugar-phosphate backbone by comparison with previous NMR studies of i-motif structures. [d(5mCCTCACTCC)]2 is built by intercalation of two symmetrical hairpins held together by six symmetrical C*C+ pairs and by pair T7*T7. The hairpin loops that are formed by a single residue, A5, cross the narrow grooves on the same side of the i-motif core. The base pair intercalation order is C9*C9+/5mC1*5mC1+/C8*C8+/C2*C2+/T7.T7/C6*C6+/C4*C4+. The T3 bases are flipped out in the wide grooves. The core of the structure includes four long-lived pairs whose lifetimes at 15 degrees C range from 100 s (C8*C8+) to 0.18 s (T7*T7). The formation rate and the lifetime of [d(5mCCTCACTCC)]2 were measured between pH 6.8 and 4.8. The dimer formation rate is three to four magnitude orders slower than that of a B-DNA duplex. It depends on pH, as it must occur for a bimolecular process involving non cooperative association of neutral and protonated residues. In the range of pH investigated, the dimer lifetime, 500 s at 0 degrees C, pH 6.8, varies approximately as 10(-pH).
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==About this Structure==
==About this Structure==
Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=2AWV OCA].
Full experimental information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=2AWV OCA].
==Reference==
==Reference==
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[[Category: Hemiprotonated cc+ pair]]
[[Category: Hemiprotonated cc+ pair]]
[[Category: I-motif]]
[[Category: I-motif]]
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Revision as of 11:40, 28 July 2008
This article has been automatically seeded. Changes to this page should pertain to the PDB entry only and not to the protein or biomolecule in general.
Full experimental information is available from OCA.
Reference
Structure, internal motions and association-dissociation kinetics of the i-motif dimer of d(5mCCTCACTCC)., Canalia M, Leroy JL, Nucleic Acids Res. 2005 Oct 4;33(17):5471-81. Print 2005. PMID:16204453
