Recognition of Nine Base Pair Sequences in the Minor Groove of DNA at Subpicomolar Concentrations by a Novel Microgonotropen

Abstract

The dsDNA interactions of the novel microgonotropen L1 have been characterized via spectrofluorometric titrations and thermal melting studies. A microgonotropen consists of a DNA minor groove binding moiety attached to a basic side chain capable of reaching out of the minor groove and grasping the acidic DNA phosphodiester backbone. L1 was synthesized employing solid-phase chemistry. L1 is shown to distinguish nine base pair A/T rich binding sites from sites possessing fewer than nine contiguous A/T base pairs. Further, L1 binds its preferred dsDNA sequences at subpicomolar concentrations. The equilibrium constant for complexation ( K 1) of a nine base pair A/T rich dsDNA binding site by L1 is roughly 10 13 M −1. Single base pair A/T → G/C substitutions within the nine base pair A/T rich binding site of L1 decreases the equilibrium constant for DNA binding by 1–2 orders of magnitude. The three proplyamine side chains of L1 enhance the agents free energy of binding by more than 5 kcal. Molecular modeling suggests that L1 adopts a ‘spiral-like’ conformation which fits almost a full turn of the DNA helix.