Fig. 6: Protein adsorption drives spontaneous formation of nanotubes and their transformation into double-membrane sheets at the vesicle surface.
a Glycinin phase diagram as a function of NaCl concentration. The working condition for condensate formation, and two homogeneous solutions at low and high salinity are indicated. b DOPC GUVs grown in sucrose and then diluted in isotonic solutions of the indicated NaCl concentrations show inward tubulation due to the solution asymmetry. Scale bars: 5 µm, zoomed images: 1 µm. DOPC GUVs grown at 20 mM NaCl (c) or 365 mM NaCl (d) in contact with a homogeneous glycinin solution at the same NaCl concentration display outward bud and nanotube formation. Scale bars: 5 µm. e Ratio of the protein signal intensity (FITC-glycinin) at the membrane (IMEMB) to the external solution (IOUT), indicating protein binding to the membrane, which increases with higher salinity. Individual measurements are shown as dots and the lines indicate mean ± SD (n = 10). f Particle density (reflecting the surface concentration of protein) obtained by mass photometry for 0.48 µg/mL glycinin solutions at the indicated NaCl concentration, over supported lipid bilayers of DOPC indicating higher adsorption with increasing salinity. Individual measurements are shown as dots and the lines indicate mean ± SD (n = 35). g Confocal microscopy cross-section (left) and 3D projection (right) of the membrane channel for a DOPC GUV in contact with a homogeneous glycinin solution at 365 mM NaCl. The tubes adhere to the vesicle surface and transform into double-membrane sheets; the double-membrane sheets essentially represent deflated pancake-like vesicles connected via a tube and adhering to the mother GUV. Scale bars: 5 µm. h Intensity profile across the dashed line shown in (g), indicating that the intensity for the double-membrane sheet adsorbed on the vesicle (3 bilayers) is three times higher than for the membrane (single bilayer). Source data are provided as a Source Data file.
