Figure 3. Atg8-PE stabilizes membrane curvature and sorts into strongly curved membanes.

(A) Setup used for tube pulling. After aspiration, the vesicle containing biotinolyted lipids and the streptavidin coated bead were brought in contact and adhere. Once bound, a tube was pulled by moving the pipette holding the bead, a confocal xy-scan illustrates such a membrane tube pulled from a GUV. (B) Fluorescence intensity profiles of the membrane tube (top) and the corresponding GUV membrane (bottom) of the boxed regions in (A). (C) At high Atg8-PE densities, pulled tubes appeared blurry and exhibit pronounced fluctuations. Two consecutive xy-scans of the same tube illustrate movements of the tube; see also S1 Video. (D) Increasing the membrane tension of the GUV at time t = 1 min (blue line, right axis) decreases the radius of the membrane tube from 70 nm to 16 nm and accordingly changes the intensities of the membrane tube and Atg8-PE (data points, left axis). This change is reversible as shown with decreasing the tension at time t = 7 min. For experimental details see methods. Data points correspond to consecutive scans of one individual tube. (E) The normalized Atg8-PE densities in the tube D^tube/D^GUV increase with tension. Three different Atg8 concentrations are shown, n = 7 GUVs for 0.56 and 0.63 µM Atg8, n = 3 GUVs for 0.75 µM Atg8, mean ± sem. The scale bars in (A) and (C) are 5 µm.