Fig. 2.

The molecular structure of a sterol determines separation of phases in GUVs and the curvature of the l_o phase. Confocal images of GUVs produced from DOPC:SM:sterol (1:1:1) in 12 mM sucrose. The sterols used were cholesterol, 3-ketocholesterol, lanosterol, lophenol, or cholesteryl sulfonate. GUVs in Left images are labeled with DiI-C₁₈ (red) only. Center images were taken ≈30 minutes after cholera toxin (green) has been added. Right images were taken directly after injection of 26 mM sucrose solution. Same as in the case of cholesterol, DiI-C₁₈ labeling marks the l_d phase and cholera toxin labeling marks the l_o phase for all sterols that induce phase separation (see Figs. 3 and 6, which is published as supporting information on the PNAS web site). (Scale bar: 10 μm.) The ratio of vesicles showing outward bulging (or budding) behavior to vesicles showing an inward preference was at least 10 for cholesterol and lophenol, and <1/10th for lanosterol and cholesteryl sulfonate, as judged from overview scans with many vesicles.