Visualization of Molecular Permeation into a Multi-compartment Phospholipid Vesicle

Passive permeation of small molecules into vesicles withmultiplecompartments is a critical event in many chemical and biological processes.We consider the translocation of the peptide NAF-1(44-67) labeled with a fluorescent fluorescein dye across membranes of rhodamine-labeled1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) intoliposomes with internal vesicles. Time-resolved microscopy revealeda sequential absorbance of the peptide in both the outer and innermicrometer vesicles that developed over a time period of minutes tohours, illustrating the spatial and temporal progress of the permeation.There is minimal perturbation of the membrane structure and no evidencefor pore formation. On the basis of molecular dynamics simulationsof NAF-1(44-67), we extended a local defect modelto migration processes that include multiple compartments. The modelcaptures the long residence time of the peptide within the membraneand the rate of permeation through the liposome and its internal compartments.Imaging experiments confirm the semi-quantitative description of thepermeation of the model by activated diffusion and open the way forstudies of more complex systems.