Figure 7.

The effects of cholera toxin B (CTB) and prominins on the initial formation and stability of membrane nanotubes. Due to positive spontaneous curvature of GM1 aggregates (see Figure 5B), such small GM1 aggregates would sense and stabilize small membrane protrusions A). The binding of each CTB molecule to a few GM1 aggregates would lead to the aggregation of CTB–GM1 complexes, thereby driving the coalescence of small membrane protrusions into a large spherical protrusion B). Due to flat shape of CTB it is assumed that bound CTB reduces the spontaneous curvature of GM1 aggregates. The neck region of the membrane protrusion attracts anisotropic membrane nanodomains such as prominins, which facilitate and stabilize the growth of membrane nanotubes C). The addition of anti-CTB (pentameric antibodies) may cross-link (intercalate) CTB units, thereby leading to the formation of stiff microdomains that do not allow the growing of membrane nanotubes D).