Spontaneous and protein-mediated intermembrane transfer of the antiretroviral liponucleotide 3'-deoxythymidine...

Phospholipid conjugates of antiretroviral nucleosides show activity against the human immunodeficiency virus in vitro [Hostetler, K. Y., Stuhmiller, L. M., Lenting, H. B. M., Van den Bosch, H., & Richman, D. D. (1990) J. Biol. Chem. 265, 6112-6117]. In order to gain insight into the membrane association and the spontaneous and protein-mediated intermembrane transfer of these compounds, we have synthesized the fluorescent analog 3'-deoxythymidine diphosphate 1-myristoyl-2-(10-pyren-1-yl-decanoyl)glycerol. The compound readily incorporated into ethanol-injection vesicles, but the stability of the fluorescent probe (10% of total lipid) in the lipid bilayer was less than that of 1-myristoyl-2-(10-pyren-1-yldecanoyl)phosphatidylcholine. Using a donor-acceptor vesicle assay system, half-times for spontaneous transfer at 25 and 37 degrees C were 20 and 100 min, respectively. The liponucleotide was rapidly transferred between membranes by the nonspecific lipid-transfer protein at a rate at least 10-fold that of the corresponding phosphatidylcholine. Depletion of the liponucleotide from the outer monolayer of vesicles by a large excess of nonspecific lipid-transfer protein indicated a transbilayer distribution similar to the mass distribution of phospholipids. Essentially no flip-flop of the inner monolayer liponucleotide was observed.