A model for the [C+-GxC]n triple helix derived from observation of the C+-GxC base triplet in a crystal structure.
A molecular modelling study on the [C+-GxC]n triple helix is reported. We have observed the C+-GxC base triplet in the crystal structure of an oligonucleotide-drug complex, between the minor-groove drug netropsin and the decanucleotide d(CGCAATTGCG)2. The complex was crystallised at pH 7.0, but the crystal structure, at a resolution of 2.4 A, shows that a terminal cytosine has become protonated and participates in a parallel C+-GxC base triplet. The structure of this triplet and its associated sugar-phosphate backbones have been energy-refined and then used to generate a triple helix. This has characteristics of the B-type family of DNA structures for two strands, with the third, the C+ strand, having backbone conformations closer to the A family.
Nunn
C M
CM
CRC Biomolecular Structure Unit, The Institute of Cancer Research, Sutton, Surrey, UK.
Trent
J O
JO
Neidle
S
S
D004247:DNA / Q000737:chemistry*; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D014961:X-Ray Diffraction
C051802:triplex DNA; D004247:DNA