BINDING OF DNA TO LIPOSOMES CONTAINING DIFFERENT DERIVATIVES OF SPHINGOSINE

Binding of DNA to dimyristoylphosphatidylcholine (DMPC) liposomes cont aining different sphingosine derivatives was investigated. DNA labelle d with adriamycin was used as a fluorescence quencher and its membrane association was observed by resonance energy transfer from liposomes incorporating a pyrene-derivatized lipid bisPDPC as a donor and contai ning 19 mol% of sphingosine, dihydro-, phyto- or dimethylsphingosine. As revealed by differential scanning calorimetry, the thermal phase be haviour of multilamellar liposomes containing these sphingolipids was also significantly altered by DNA. Attachment of DNA to liposomes cont aining sphingosylphosphorylcholine was much weaker, and no binding of DNA to membranes containing N-acetylsphingosine, N-stearoylsphingosine or sphingomyelin was observed. The membrane binding of DNA was depend ent on pH and could be reversed by the inclusion of phosphatidic acid (eggPA) into the liposomes. Analogously, the association of cytochrome c with eggPA could be reversed by the DNA-binding sphingosines. These findings lend support to our previous proposal that the DNA-sphingosi ne interaction is electrostatic and requires the presence of a positiv e charge in the latter. Accordingly, sphingosines carrying a protonate d amino group attach DNA to membranes, while blocking of the amino gro up by N-acylation abolishes this interaction.