Fig. 3.

Wave propagation requires F-BAR and its curvature sensitivity. a Model phase diagram showing the dependence of traveling waves on a proper balance between the curvature-dependent F-BAR-recruitment rate and the characteristic membrane curvature that recruits F-BAR. The red dot represents the model parameter set that generated the nominal model results in Figs. 1 and 2. b Double knockdown (DKD) of FBP17 and CIP4 by shRNA causes a reduction (P = 0.0008, Student’s t-test) in the percentage of cells with active Cdc42 (CBD-GFP) waves (4 experiments with 39 cells in total), comparing to wild-type (WT) cells (14 experiments with 133 cells). Error bars: s.e.m. c F-BAR domain of FBP17 is replaced with other membrane-binding motifs. Ranges of curvature (radius⁻¹) preferences of different membrane-binding domains are plotted^{24, 25, 44, 45}. Gray area indicates the curvature range that allows wave formation, corresponding to the gray area of a. d The curvature of F-BAR domain is critical for wave formation. A micrograph and a kymograph for each mutant protein both in WT and DKD conditions are shown. Only the mutant protein with an F-BAR (FCHo1) domain could rescue wave formation in DKD cells. e The ability of point mutants of F-BAR domain of FBP17 to localize to the waves in WT cells or rescue wave formation in DKD cells correlates with their tubulation activities in vitro. Representative kymographs of cells expressing point mutants or full-length construct of FBP17-GFP in WT cells and DKD cells are shown. Mutants are separated into four groups based on curvature-generating abilities. Scale bar: 10 μm