Fourier transform Raman study of the structural specificities on the interaction between DNA and biogenic polyamines

Biogenic polyamines putrescine, spermidine, and spermine are essential mole cules for proliferation in all living organisms. Direct interaction of poly amines with nucleic acids has been proposed in the past based on a series o f experimental evidences, such as precipitation, thermal denaturation, or p rotection. However, binding between polyamines and nucleic acids is not cle arly explained. Several interaction models have also been proposed, althoug h they do not always agree with one another. In the present work, we make u se of the Raman spectroscopy to extend our knowledge about polyamine-DNA in teraction. Raman spectra of highly polymerized calf-thymus DNA at different polyamine concentrations, ranging from 1 to 50 mM, have been studied for p utrescine, spermidine, and spermine. Both natural and heavy water were used as solvents. Difference Raman spectra have been computed by subtracting th e sum of the separated component spectra from the experimental spectra of t he complexes. The analysis of the Raman data has supported the existence of structural specificities in the interactions, at least under our experimen tal conditions. These specificities lead to preferential bindings through t he DNA minor groove for putrescine and spermidine, whereas spermine binds b y the major groove. On the other hand, spermine and spermidine present inte rstrand interactions, whereas putrescine presents intrastrand interactions in addition to exo-groove interactions by phosphate moieties.