SnapShot: Membrane Curvature Sensors and Generators

Cells and intracellular organelles are enclosed by bilayer lipid membranes, whose curvatures define their shape. Generation of bilayer curvature is critical for organelle biogenesis and to mediate vectorial transport from one membrane to another via vesicular or tubular intermediates. Membrane curvature can be driven by lipid perturbations that create asymmetry in the two leaflets of the bilayer, by bilayer binding and/or penetrating proteins, or by forces applied to membranes by the cytoskeleton. This SnapShot provides an overview of the mechanisms through which these proteins generate and/or sense curvature. These two properties are tightly interconnected. Proteins that initiate curvature by inserting a wedge in the bilayer (for example, amphipathic helices and hydrophobic loops) will bind preferentially to a precurved bilayer, where bending has created a gap in lipid packing. Likewise, proteins that function primarily as curved scaffolds generally assemble into polymers that propagate curvature, and their binding to the bilayer and their polymerization are both facilitated by a precurved surface. In some proteins, both scaffold mechanisms and wedge-based mechanisms cooperate. Major mechanisms of protein-driven membrane deformation are listed below. Examples given refer to structures and schematic cartoons shown in the figure.