MOLECULAR-STRUCTURE OF THE A-TRACT DNA DODECAMER D(CGCAAATTTGCG) COMPLEXED WITH THE MINOR-GROOVE BINDING-DRUG NETROPSIN

The molecular structure of the complex between the minor groove binding drug netropsin and the dodecamer d(CGCAAATTTGCG) has been solved and refined by X-ray diffraction analysis to an R-factor of 19.8% and 2.2-angstrom resolution. The drug lies in the narrow minor groove of the B-DNA fragment, covering five of the six A.T base pairs (from A5.T20 to T9.A16). The long six A.T base pair tract allows the drug to bind in a position that optimizes its contacts with the DNA, establishing hydrogen bonds with O2 of thymines and N3 of adenines. The DNA molecule shows a high propeller twist only at the A6.T19 step of the A-tract. Two three-centered hydrogen bonds are observed in the major groove at half of the A-tract.