Document Detail

The first example of a Hoogsteen base-paired DNA duplex in dynamic equilibrium with a Watson-Crick base-paired duplex--a structural (NMR), kinetic and thermodynamic study.
MedLine Citation:
PMID:  11444368     Owner:  NLM     Status:  MEDLINE    
A single-point substitution of the O4' oxygen by a CH2 group at the sugar residue of A6 (i.e. 2'-deoxyaristeromycin moiety) in a self-complementary DNA duplex, 5'-d(C1G2C3G4A5A6T7T8C9G10C11G12)2(-3), has been shown to steer the fully Watson-Crick basepaired DNA duplex (1A), akin to the native counterpart, to a doubly A6:T7 Hoogsteen basepaired (1B) B-type DNA duplex, resulting in a dynamic equilibrium of (1A)<==>(1B): Keq = k1/k(-1) = 0.56+/-0.08. The dynamic conversion of the fully Watson-Crick basepaired (1A) to the partly Hoogsteen basepaired (1B) structure is marginally kinetically and thermodynamically disfavoured [k1 (298K) = 3.9 0.8 sec(-1); deltaHdegrees++ = 164+/-14 kJ/mol; -TdeltaS degrees++ (298K) = -92 kJ/mol giving a deltaG degrees++ 298 of 72 kJ/mol. Ea (k1) = 167 14 kJ/mol] compared to the reverse conversion of the Hoogsteen (1B) to the Watson-Crick (1A) structure [k-1 (298K) = 7.0 0.6 sec-1, deltaH degrees++ = 153 13 kJ/mol; -TdeltaSdegrees++ (298K) = -82 kJ/mol giving a deltaGdegrees++(298) of 71 kJ/mol. Ea (k-1) = 155 13 kJ/mol]. Acomparison of deltaGdegrees++(298) of the forward (k1) and backward (k-1) conversions, (1A)<==>(1B), shows that there is ca 1 kJ/mol preference for the Watson-Crick (1A) over the double Hoogsteen basepaired (1B) DNA duplex, thus giving an equilibrium ratio of almost 2:1 in favour of the fully Watson-Crick basepaired duplex. The chemical environments of the two interconverting DNA duplexes are very different as evident from their widely separated sets of chemical shifts connected by temperature-dependent exchange peaks in the NOESY and ROESY spectra. The fully Watson-Crick basepaired structure (1A) is based on a total of 127 intra, 97 inter and 17 cross-strand distance constraints per strand, whereas the double A6:T7 Hoogsteen basepaired (1B) structure is based on 114 intra, 92 inter and 15 cross-strand distance constraints, giving an average of 22 and 20 NOE distance constraints per residue and strand, respectively. In addition, 55 NMR-derived backbone dihedral constraints per strand were used for both structures. The main effect of the Hoogsteen basepairs in (1B) on the overall structure is a narrowing of the minor groove and a corresponding widening of the major groove. The Hoogsteen basepairing at the central A6:T7 basepairs in (1B) has enforced a syn conformation on the glycosyl torsion of the 2'-deoxyaristeromycin moiety, A6, as a result of substitution of the endocyclic 4'-oxygen in the natural sugar with a methylene group in A6. A comparison of the Watson-Crick basepaired duplex (1A) to the Hoogsteen basepaired duplex (1B) shows that only a few changes, mainly in alpha, sigma and gamma torsions, in the sugar-phosphate backbone seem to be necessary to accommodate the Hoogsteen basepair.
J Isaksson; E Zamaratski; T V Maltseva; P Agback; A Kumar; J Chattopadhyaya
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of biomolecular structure & dynamics     Volume:  18     ISSN:  0739-1102     ISO Abbreviation:  J. Biomol. Struct. Dyn.     Publication Date:  2001 Jun 
Date Detail:
Created Date:  2001-07-10     Completed Date:  2001-12-26     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  8404176     Medline TA:  J Biomol Struct Dyn     Country:  United States    
Other Details:
Languages:  eng     Pagination:  783-806     Citation Subset:  IM    
Department of Bioorganic Chemistry, University of Uppsala, Sweden.
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MeSH Terms
Base Pairing*
DNA / chemistry*
DNA, Antisense / chemistry
Deoxyadenosines / chemistry
Nuclear Magnetic Resonance, Biomolecular
Nucleic Acid Conformation*
Nucleic Acid Hybridization
Reg. No./Substance:
0/DNA, Antisense; 0/Deoxyadenosines; 57345-51-4/2'-deoxyaristeromycin; 9007-49-2/DNA

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