Figure 5. Effect of hydrophobic mismatch on Lo domain formation and membrane fusion.

(a) Effect of saturated lipid component on lipid mixing. 1 μM HIV-FP was added to 50 μM LUVs composed of DSPC/DOPC/DOPS/Ch (2:1:1:1; blue), DPPC/DOPC/DOPS/Ch (2:1:1:1; green), DMPC/DOPC/DOPS/Ch (2:1:1:1; red) and DLPC/DOPC/DOPS/Ch (2:1:1:1; black). (b) Initial rates of lipid mixing as function of HIV-FP concentration. Same colour designations are used as in a. Data are mean±s.d. from three experiments. (c) Fusion between LUVs and SLB. LUVs and SLBs were composed of saturated lipid/DOPC/DOPS/Ch (2:1:1:1). The saturated lipids are DLPC, DMPC, DPPC or DSPC as indicated. LUVs were added to SLBs which were pre-incubated with 5 μM HIV-FP for 10 min. The images were acquired 20 min after vesicle addition. Fluorescence micrographs of SLBs labelled with 0.1 mol% Rh-PE (top row), TIRF micrographs of bound/fused LUVs labelled with 0.5 mol% DiD on SLB (middle row), and merged images (bottom row). The scale of all images is 64 × 64 μm². (d) Representative single-LUV fusion events on SLBs including docking, hemifusion and full fusion. Time zero is defined as the first frame with a visible liposome. The insets show TIRF microscopy images of representative times (s) for each type of fusion event. The scale of all inset images is 2.5 × 2.5 μm². (e) Relative frequencies of single-LUV docking (black), hemifusion (red) and full fusion (green) events.