Fig. 4: Formation of membrane-anchored actin rings.

a Membrane-binding promotes ring formation. Shown is the probability of the formation of single actin rings in GUVs (i.e., GUVs with one single unbranched actin bundle connected into a ring) in the absence or presence of membrane-anchoring. Data are shown as mean values with individual fractions of experimental runs. Three hundred ninety two vesicles between 15 and 20 µm were analyzed in n = 2 (fascin) or n = 3 experimental runs per condition. We use 2 µM actin in all cases, but due to differences in bundling activity different concentrations of bundling protein: 0.3 µM fascin, 1 µM α-actinin, 2 µM talin, and 2 µM vinculin. b Probability of ring formation for simulations with different initial parameters (R: vesicle radius, L: filament lengths). In simulations, we classified rings with small gaps or closed rings with additional side branches as “ring like” (see Supplementary Method). Snapshots from all simulation shown in Supplementary Fig. 11. c Condition with particularly robust ring formation: actin bundled by talin with vinculin and bound to the membrane. Supplementary Movie 4 shows a 3D view of this image. Supplementary Figure 8 shows a DIC image of this field of view, and Supplementary Figs. 9 and 10 show rings formed by other bundling proteins.