Study of the G-quadruplex–dipalmitoylphosphatidylcholine interactions at the air/water interface

The surface film balance studies of dipalmitoylphosphatidylcholine (DPPC) monolayer and mixed monolayers of DPPC and a cationic dioctadecyldimethylammonium bromide (DODAB) surfactant in the presence of 22-mer quadruplex-forming DNA oligonucleotide bearing human telomere sequence of dAG3(T2AG3)3 (G4 DNA) are reported. Insight into processes related to the G4 DNA–monolayer interactions was provided by differences in profiles of π–A isotherms recorded in the presence and absence of G4 DNA on subphases with varied composition. The G4 DNA–monolayer interactions were also studied by recording time profiles of the surface pressure of monolayer at a constant mean molecular area, while perturbants (G4 DNA and/or KCl) were sequentially injected under the monolayer surface.The surface pressure balance study indicated that interactions of G4 DNA with zwitterionic DPPC monolayer do not occur. The importance of monolayer charge on the ability of G4 DNA to adsorb on the monolayer interface was evidenced for mixed DPPC/DODAB monolayers and DPPC monolayers modified by incorporation of divalent metal ions. Shifts of isotherms towards lower molecular areas in the presence of G4 DNA were observed when compared with the reference isotherms recorded on subphases without G4 DNA.

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► G-quadruplex (G4 DNA) does not interact with zwitterionic lipid monolayer at the air–water interface.
► G4 DNA shifted π–A isotherm of the mixed zwitterionic/cationic lipid film to lower molecular areas.
► Extent of shift in π–A isotherm depended on the charge density of monolayer interface.
► Diffusion rate of DNA molecules to monolayer increased with its charge density.