Figure 4. Mechanisms of membrane-curvature induction.

Several mechanisms of membrane deformation by cellular proteins have been described. a | Integration of membrane proteins that have a conical shape induces curvature, as they act like a wedge that is inserted into the membrane. b | Amphipathic helices, stretches of alpha helices that have one polar and one hydrophobic side, are positioned flat on the membrane, with the hydrophobic side dipping into one of the two membrane layers: this causes destabilization of the membrane and membrane bending. c,d | Membrane bending can be induced by oligomerization of proteins that are integrated into, or associated with, cellular membranes. Proteins form a scaffold that makes the membrane bend. e | The lipid composition of a membrane can also induce membrane curvature. In this context, the head group, as well as the acyl chain of the membrane constituents, can have an effect on membrane curvature. Figure adapted, with permission, from Nature Ref. 79 © (2005) Macmillan Publishers Ltd.