The sequence specific binding of the antibiotic (4S)‐(+)‐dihydrokikumycin B and its (4R)‐(−)enantiomer, [(S)‐I and (R)‐I, respectively] to DNA were characterized by DNase I and MPE footprinting, calorimetry, UV, spectroscopy, circular dichroism, and 1H NMR studies. Footprinting analyses showed that both enantiomers [(S)‐I and (R)‐I] bind to AT‐rich regions of DNA. 1H NMR studies (ligand induced chemical shift changes and NOE differences) of the dihydrokikumycins with d‐[CGCAATTGCG]2 show unambiguously that the N to C termini of the ligands are bound to 5′‐A5T6T7‐3′ reading from left to right. From quantitative 1D‐NOE studies, the AH2(5)‐ligand H7 distance of complex A [(S)‐I plus decamer (which is bound more strongely)] and complex B[(R)‐I and decamer] are estimated to be 3.8 ± 0.3 Å and 4.9 ± 0.4 Å, respectively. This difference in binding properties is reflected in the thermodynamic profiles of the two enantiomeric ligands determined by a combination of spectroscopic and calorimetric techniques. The binding freee energies (ΔG°) of (S)‐I and (R)‐I to poly d(AT)·poly d(AT) at 25°C are −31.8 and −29.3 kJ mol−1, respectively while the corresponding binding enthalpies (ΔH°) are −11.3 and −0.8 kJ mol−1. These data permit the construction of models for the binding of the enantiomeric dihydrokikumycins to DNA and account for the more efficient binding of the natural (S) isomer to DNA.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Structural Biology