The tertiary structure of a DNA aptamer which binds to and inhibits thrombin determines activity.

The solution-state three-dimensional structure of the DNA aptamer d(G 1 G 2 T 3 T 4 G 5 G 6 -T 7 G 8 T 9 G 10 G 11 T 12 T 13 G 14 G 15 ) which binds to and inhibits thrombin has recently been determined by NMR methods (Wang et al., 1993). This DNA adopts a highly compact, highly symmetrical structure which consists of two tetrads of guanosine base pairs and three loops. The basic features of this three-dimensional structure are preserved when the aptamer binds to thrombin. The three-dimensional structure can be used as a basis for interpreting the relative activities of modified aptamers as well as for proposing a model for the aptamer-thrombin complex