Cookies on this website
We use cookies to ensure that we give you the best experience on our website. If you click 'Continue' we'll assume that you are happy to receive all cookies and you won't see this message again. Click 'Find out more' for information on how to change your cookie settings.

The structures of d(GAAGAGAAGC).d(GCTTCTCTTC), d(GAAGAGAAGC). r(GCUUCUCUUC), r(GAAGAGAAGC).d(GCTTCTCTTC), and r(GAAGAGAAGC). r(GCUUCUCUUC) have been determined in solution from NMR data. Globally, the pure DNA and RNA duplexes were in the B and A forms, respectively. The two DNA.RNA hybrids were neither A nor B, but closer globally to the A than the B form. However, the thermodynamically less stable d(GAAGAGAAGC).r(GCUUCUCUUC) duplex has a significantly different conformation from r(GAAGAGAAGC). d(GCTTCTCTTC). Structures were calculated based on the NMR data, using restrained molecular dynamics. A new approach to the treatment of conformational averaging based on a prioriprobabilities has been used. The nucleotides were treated by fitting the scalar coupling data and NOE time courses to a two-state model comprising N and S sugar puckers each with a different glycosidic torsion angle, and the mole fraction of the S state. Restraint sets for different distributions of N and S states within molecules were constructed, such that each nucleotide was weighted in the ensemble according to the mole fractions (or a prioriprobabilities). The individual nucleotide conformations were strongly restrained, whereas the internucleotide restraints were set relatively loosely. Ensembles of conformations were generated and assessed by comparison of the NOEs calculated from ensemble-averaged relaxation matrices with the experimental NOEs. The ensemble averages accounted for the experimental data much better than any individual member, or for structures calculated assuming a single unique conformation. The two hybrids populated different degrees of conformational space. There was a general trend in minor and major groove widths in the order d(GAAGAGAAGC).d(GCTTCTCTTC), d(GAAGAGAAGC).r(GCUUCUCUUC), r(GAAGAGAAGC).d(GCTTCTCTTC), r(GAAGAGAAGC).r(GCUUCUCUUC) and a similar progression in global character from B-like to A-like structures. Furthermore, r(GAAGAGAAGC).d(GCTTCTCTTC) showed a greater dispersion of conformations in the ensemble than d(GAAGAGAAGC).r(GCUUCUCUUC), reflecting the greater flexibility of the sugars. If conformational averaging of the nucleotides is ignored, incorrect virtual structures are produced that nevertheless are able to satisfy a substantial fraction of the experimental data.

Original publication

DOI

10.1021/bi9719713

Type

Journal article

Journal

Biochemistry

Publication Date

06/01/1998

Volume

37

Pages

73 - 80

Keywords

Crystallography, X-Ray, DNA, Deoxyribose, Magnetic Resonance Spectroscopy, Models, Molecular, Nucleic Acid Conformation, Nucleic Acid Heteroduplexes, Purine Nucleotides, Pyrimidine Nucleotides, RNA, Sequence Homology, Nucleic Acid, Solutions