Exploring the intercalation binding of tiamulin with DNA using multispectroscopy and a molecular modelling approach

The binding of tiamulin with calf thymus DNA was systematically investigated using multispectroscopy and molecular modelling techniques. For DNA, once tiamulin was added, viscosity (η) and melting temperature (T_m ) both exhibited an uptrend. The fluorescence performance of the tiamulin-DNA complex did not change with the ionic strength changes. The binding constant (K_a ) of tiamulin for single-stranded DNA (ssDNA, 1.48 × 10⁴  M^-1 ) was obviously higher than that for double-stranded DNA (dsDNA, 9.51 × 10³  M^-1 ) at 291 K. The helix structure became looser and the base stack force became stronger for DNA due to the presence of tiamulin as seen from circular dichroic (CD) spectra. The intercalation binding mode of tiamulin with DNA was disclosed. Molecular modelling also revealed tiamulin inserting into the base pairs with the lowest binding free energy of -18.73 kJ mol^-1 using van der Waals forces as well as hydrogen bonds.