A molecular mechanics study of spermine complexation to DNA: a new model for sperm ine-poly(dG-dC) binding

Abstract
Molecular mechanics calculations of the binding of spermine to a number of solvated DNA helices have led to the development of a new model for spermine complexation. The structural details of the complexes formed with d(GCG CGCGGC )2 and d (ATATATATAT) 2 decamers allowed a rationalization of the observed experimental differences for binding to these two helices. Ford (ATATATA AT) 2 it was concluded that spermine remains in a cross-major groove binding site. Conversely, for d(GCGCGCGCGC) 2 spermine reorientation via specific ligand—base-pair hydrogen-bond formation allows complexation along the major groove. The solvent plays an important role in differentiating the two binding modes. A mechanism of spermine complexation to natural DNA is postulated from these results. Past experimental data are also considered in the context of the new model.