An X-ray diffraction study of complexes of DNA and lactosyl-functionalised liposomes induced by bivalent metal cations: coexistence of different symmetries

By using synchrotron X-ray diffraction we studied the structure and phase behaviour of complexes of DNA with the anionic 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-lactosyl (L-PE), mixed with zwitterionic lipids 1,2-dioleoyl-sn-glycero 3-phosphocholine (DOPC) or 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), in aqueous solutions of Mn2+ and Ca2+. Aqueous dispersions of simple L-PE/DOPC and L-PE/DOPE in the presence and absence of metal cations were also studied. All the systems complexed in a self-assembled manner, the DNA condensation being promoted by the metal cations. These complexes are organised in a variety of structures showing a number of symmetries, sometimes coexisting, for example condensed multilamellar, Lαc, inverted hexagonal, HIIc, and cubic, Pn3m. Phase distribution depends on the molar ratios between L-PE and DOPC or DOPE, respectively.