Septins recognize micron-scale positive membrane curvature. (A) Supported lipid bilayer (25% PI and 75% PC) and trace Rh-PE–coated silica beads ranging from 0.3 to 6.5 µm in diameter mixed with 50 nM S. cerevisiae septin complex containing Cdc11-SNAP488 for visualization. The Rh-PE is shown in magenta, and Cdc11-SNAP488 is shown in green. (B) Mean intensity images of 10 beads for each condition. (C) Septin adsorption to each bead size at 100-nM septin complex. (D) Septin adsorption to beads as a function of concentration. (E) Heat map of fold difference in septin adsorption to beads as a function of concentration. Data were normalized to the lowest detectable septin adsorption, on 1-µm beads at 10-nM septin complex concentration. 500 nM was the highest experimentally attainable septin complex concentration that could be mixed with beads. In C–E, n ≥ 32 for each size, and error bars represent standard error. Dunn test results: ***, P < 0.005; *, P < 0.05. n.s., not significant.