Figure S1.
Graph A shows the individual probability (n equals k) for 0 to 4 C T x B molecules. As the O M D diameter increases from 0 to 100 nanometer, the probability for k equals 0 (black) drops sharply, while k equals 1 (red), k equals 2 (cyan), k equals 3 (green), and k equals 4 (purple) show successive peaks at approximately 30 nanometer, 45 nanometer, 55 nanometer, and 70 nanometer, respectively. Graph B displays the cumulative probability (k greater than or equal to 2) of multiple C T x B molecules occupying a single O M D. The probability follows a sigmoid curve, starting near 0 at 10 nanometers and reaching a plateau of 1.0 (certainty) at approximately 80 nanometers. Graph C shows similar occupancy peaks as Graph A, but the higher G M 1 density causes the shift toward multiple occupancy to occur at smaller O M D diameters. For example, the peak for k equals 1 (red) occurs earlier, at roughly 20 nanometers. Graph D shows the cumulative probability (k greater than or equal to 2) for 1 percent G M 1 density, which also follows a sigmoid curve but reaches its 1.0 plateau faster than the 0.5 percent density, at approximately 60 nanometers. All values are approximate.
Poisson statistics–based simulations illustrating the increased probability of CTxB binding as OMD size increases. (A–D) Relative to simulations using 2 mol% GM1 (Fig. 2), simulations shown here assume lower GM1 densities within OMDs: 0.5 mol% (A and B) and 1 mol% (C and D). Within a given cell type, GM1 density within OMDs is assumed to remain constant.