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| | {{STRUCTURE_1q2t| PDB=1q2t | SCENE= }} | | {{STRUCTURE_1q2t| PDB=1q2t | SCENE= }} |
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| - | '''Solution structure of d(5mCCTCTCC)4'''
| + | ===Solution structure of d(5mCCTCTCC)4=== |
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| - | ==Overview==
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| - | The i-motif is a four-stranded structure built by intercalation in head-to-tail orientation of two parallel duplexes associated by hemi-protonated C.C(+) pairs. Using NMR methods, we investigated the structure, the base-pair opening kinetics and the internal motions of three i-motif tetramers: [d(5mCCTCnTCC)](4) (n=1, 2, 3). These tetramers cannot accommodate the intercalation of two T.T pairs in face-to-face orientation. They are built by intercalation of two symmetrical duplexes whose contacting T3/TM thymidine bases (M=5, 6, 7) are either base-paired or unstacked. The arrangement of the unstacked/paired thymidine bases of the two T/T groups results in the formation of two different conformations. One, fully symmetric, whose thymidine bases T3 and TM are unstacked and base-paired respectively. The other is the asymmetric assembly of two duplexes: one where both thymidine bases are unstacked and the other with two T.T pairs. The proportion of the symmetric conformer increases from a value beyond the detection threshold for n=1, to 19% for n=2 and up to more than 95% for n=3. The exchange cross-peaks connecting together the intercalated duplexes of [d(5mCCTCTCC)](4) and [d(5mCCTCCTCC)](4) reveal a structural interconversion induced by the simultaneous opening/closing of the contacting T3/TM thymidine bases. In [d(5mCCTCCTCC)](4) the motion of the T3/T6 groups triggers the interconversion of the symmetric and asymmetric conformations. In [d(5mCCTCTCC)](4) the intercalated duplexes exchange their structures in an apparently concerted motion, suggesting the simultaneous opening/closing of two distant T3/T5* and T5/T3* switching groups. The spectrum of [d(5mCCTCCCTCC)](4) is fully symmetric and, for this reason, its spectrum gives no indication for duplex interconversion. Nevertheless, the imino proton exchange kinetics argues for a switching motion of the T3/T7 group. Duplex interconversion is not detectable in that case, due to the tetramer symmetry. The origin of the structural conflict hindering the intercalation of two T.T pairs into the i-motif is discussed.
| + | The line below this paragraph, {{ABSTRACT_PUBMED_14516748}}, adds the Publication Abstract to the page |
| | + | (as it appears on PubMed at http://www.pubmed.gov), where 14516748 is the PubMed ID number. |
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| | + | {{ABSTRACT_PUBMED_14516748}} |
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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=1Q2T OCA]. | + | Full experimental information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1Q2T OCA]. |
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| | ==Reference== | | ==Reference== |
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| | [[Category: I-motif]] | | [[Category: I-motif]] |
| | [[Category: Protonated cytidine]] | | [[Category: Protonated cytidine]] |
| - | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sat May 3 05:47:43 2008'' | + | |
| | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jul 28 21:33:52 2008'' |
Revision as of 18:33, 28 July 2008
Template:STRUCTURE 1q2t
Solution structure of d(5mCCTCTCC)4
Template:ABSTRACT PUBMED 14516748
About this Structure
Full experimental information is available from OCA.
Reference
T.T pair intercalation and duplex interconversion within i-motif tetramers., Leroy JL, J Mol Biol. 2003 Oct 10;333(1):125-39. PMID:14516748
Page seeded by OCA on Mon Jul 28 21:33:52 2008
