Stabilization of the Noncomplementary Guanine−Adenine Base Pairs by Zn(II) Ions. An ab Initio SCF-MI Study

Abstract

The structure and energy of the guanine (G)−adenine (A) base pairs in the G(anti)−A(anti) and G(anti)−A(syn) conformations as well as their complexes with hydrated zinc(II) ions have been investigated by the self-consistent field for molecular interaction (SCF-MI) ab initio method. The formation of covalent bonds between the Zn(II) ions and the N7 sites of the guanine bases results in an increase of the binding energy of the G−A pairs. In addition, the SCF-MI calculations have also been performed for the guanine (G)−guanine (G)−cytosine (C) (G−GC) base triplet and for its complex with a hydrated Zn(II) ion bound to the N7 site of the third-strand guanine. The Zn(II) binding causes a significant stabilization of the G−GC triplet. Possible implications for the conformational changes in alternating d(GA)n sequences are discussed.