Cellular membranes are made up of lipid bilayers that can be highly curved, an essential feature critical for processes such as endocytosis, organelle synthesis, cell division, and intracellular transport. Current understanding suggests that specialized proteins are responsible for membrane curvature through two mechanisms.Mechanisms causing membrane curvature.
- Membrane scaffolding by proteins or complexes that assemble into a curved shape: These scaffolding proteins can bend membranes using anchors that cause the membrane to follow the contour of the protein. Proteins such as amphiphysin and dynamin are thought to act as scaffolds that form thin membrane necks prior to separation of the membrane regions (fission).
- The other mechanism thought responsible for membrane bending involves proteins with wedge-like helices that contains parts that are amphipathic, meaning they are both oil-loving (lipophilic) and water-loving (hydrophilic). These helices partially insert themselves into the lipophilic membrane and push the lipid molecules apart.
Combustion Research Facility (CRF) researchers Carl Hayden (Combustion Chemistry Dept.), Darryl Sasaki (Biotechnology & Bioengineering Dept.), and Jeanne Stachowiak (now at the University of Texas, Austin), along with collaborators Eva Schmid and Daniel Fletcher at the University of California–Berkeley, and others, now propose a third mechanism for bending cellular membranes: protein-protein crowding.
This work was supported by DOE BES: Division of Materials Science and Engineering and Division of Chemical Sciences, Geosciences, and Biosciences; the Sandia LDRD program; the NIH NIGMS and Nanomedicine Development Centers; a Sealy and Smith Foundation grant to the Sealy Center for Structural Biology and Molecular Biophysics; and the Miller Institute for Basic Research in Science.