Membrane Shape and the Regulation of Biological Processes

Biological membranes define and determine the architecture, i.e., shape, of cells and organelles. While most membranes present a planar morphology on the nanometer length scale, their shape could change in a wide range of length and time scales, leading to more intricate shapes that could be (transient) short- or long-lived. The change in membrane shape from the energetically more stable planar one is accomplished by bending it away (curving) from this morphology, a process that is determined by the lipid bilayer structural properties and/or the application of forces by proteins. For a long time, the membrane shape was believed to play a passive role. However, recently this view has started changing by examples of biological processes controlled by the membrane shape and/or its curved structures, which poses membrane shapes as active modulators of signaling in biological processes. The ability of membrane shape and/or its curved structures to regulate biological processes usually occurs either by a preferential binding of proteins to membranes or the allosteric regulation of enzymes by membrane shape changes. Here, the current knowledge of the roles of membrane shape on the regulation of biological processes will be discussed. While the role of membrane shape is usually tied up with the bilayer bending properties, recent reports showed that some proteins prefer a planar membrane shape instead of curved structures. Hence, it is here proposed that membrane shape recognition is a trigger for signaling events. We present examples in which different membrane shapes stimulate protein binding and/or enzyme activity.