Fig. 2: Spontaneous curvature and morphology diagram.
From: Controlled division of cell-sized vesicles by low densities of membrane-bound proteins
a Spontaneous curvature m generated by GFP coverage Γ: We studied four vesicle populations with four different GFP coverages as obtained for 0.1 mol% anchor-lipids and molar GFP concentrations X = 0.78, 7.8, 15.6, and 23.4 nM. For the two lower concentrations X = 0.78 and 7.8 nM, the dummbell-shaped vesicles were imaged by confocal microscopy, whereas we used STED microscopy to resolve the small buds formed for the higher concentrations X = 15.6 and 23.4 nM. For each vesicle population, we selected the three vesicles with the largest neck curvature Mne as defined in Eq. (5) from at least three independent experiments. These three curvature values provide the three data points (black squares, red triangles, green circles) included for each Γ-value. The straight line represents the least-squares fit through the black squares and has a slope of about 27 nm (\(R^{2}_{\mathrm{adj}} \simeq 0.98\)). b Confocal and STED images of small buds as obtained for GFP concentrations X = 15.6 and 23.4 nM. For the analysis of the STED images, see Supplementary Fig. 2. c Morphology diagram as a function of two dimensionless shape parameters, the rescaled spontaneous curvature mRve and volume-to-area ratio v. Dumbbell-shaped vesicles with a closed membrane neck are found between the two dashed lines L1+1 and L2* (blue). The latter subregion contains the dash-dotted line, at which the spherical buds become unstable and transform into prolate buds. The shapes denoted by A, B, and C correspond to three GUVs in the absence of GFP. Adding GFP to the exterior solution, the three GUVs transformed into the dumbbell shapes A\({}^{\prime}\), B\({}^{\prime}\), and C\({}^{\prime}\). d Confocal images of the six vesicle shapes A, B, and C (left column) as well as A\({}^{\prime}\), B\({}^{\prime}\), and C\({}^{\prime}\) (right column). The white arrows indicate the positions of the closed membrane necks. The corresponding parameter values are displayed in Table 1. All scale bars: 5 μm. Source data for panels a and c are provided in the Source Data file.
