Crystal structure of right-handed Z-DNA in complex with the polyamine cadaverine and potassium cations at ultrahigh resolution

An ultrahigh-resolution crystal structure of right-handed Z-DNA with the sequence L-d(CGCGCG)2 reveals the pattern of cadaverinium2+ and K+ binding. The complete polyamine dication is well visible in the electron density and assumes a position that allows for H-bond interactions with two Z-DNA duplexes. The K+ cation occupies a mixed K+/H2O site and forms a irregular coordination sphere interacting with water molecules and O atoms of two phosphate groups of two Z-DNA molecules, with some of the ligands present at fractional occupancy.