title: The structural diversity of DNA-neutral phospholipids-divalent metal cations aggregates: a small-angle synchrotron X-ray diffraction study.
abstract: We investigate the structure of aggregates formed due to DNA interaction with saturated neutral phosphatidylcholines [dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylcholine] in presence of Ca(2+) and Mg(2+) cations using simultaneous synchrotron small- and wide-angle X-ray diffractions. For DPPC:DNA = 3:1 mol/base and in the range of 1-50 mM Ca(2+), the diffractograms show structural heterogeneity of aggregates. We observe the coexistence of two lamellar phases in aggregates prepared at 1 mM Ca(2+): L(x) phase with the DNA strands (of unknown organization) intercalated in water layers between adjacent lipid bilayers and L(DPPC) phase of DPPC bilayers without any divalent cations and DNA strands. Aggregates prepared in the range 2-50 mM Ca(2+) show a condensed gel lamellar phase L (g) (c) with the lipid bilayer periodicity d approximately 8.0 nm, and the DNA-DNA interhelical distance d (DNA) approximately 5.1 nm. The increase of temperature induces the decrease in the intensity and the increase in the width of the DNA related peak. In the fluid state, the condensed lamellar phase L (alpha) (c) gradually converts into L(x) phase. The aggregates do not exhibit rippled P(beta) phase. The thermal behaviour of aggregates was investigated in the range 20-80 degrees C. Applying heating-cooling cycles, the aggregates converted into energetically more favourable structure: a condensed lamellar phase L(c) (or L(x)) is preserved or we observe lateral segregation of the DNA strands and metal cations (L(x) phase) in coexistence with L(PC) phase of pure phospholipids.
authors.affiliation: Department of Physical Chemistry of Drugs, Faculty of Pharmacy, Comenius University, Bratislava, Slovakia. daniela.uhrikova@fpharm.uniba.sk
authors.forename: Daniela
authors.initials: D
authors.lastname: Uhríková
authors.forename: Adrián
authors.initials: A
authors.lastname: Lengyel
authors.forename: Mária
authors.initials: M
authors.lastname: Hanulová
authors.forename: Sérgio S
authors.initials: SS
authors.lastname: Funari
authors.forename: Pavol
authors.initials: P
authors.lastname: Balgavý
mesh_terms: D002412:Cations; D003198:Computer Simulation; D004247:DNA / Q000737:chemistry*; D004337:Drug Carriers / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D046911:Macromolecular Substances / Q000737:chemistry; D008670:Metals / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D010743:Phospholipids / Q000737:chemistry*; D055672:Static Electricity; D017356:Synchrotrons; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D002412:Cations; D004337:Drug Carriers; D008081:Liposomes; D046911:Macromolecular Substances; D008670:Metals; D010743:Phospholipids; D004247:DNA