October 11, 2012

When in a crowded elevator, mall, or football stadium, I panic knowing that I’d be the first person trampled and/or eaten in an emergency. Crowded places give me the willies, but when proteins are over-crowded, interesting things happen. Today’s image is from a paper showing what can happen at the membrane when proteins are over-crowded. 

Membrane bending is an essential part of many cellular events, including endocytosis and filopodia formation. It has been suggested that membrane curvature can stem from two mechanisms—the use of curved proteins to form a curved scaffold for the membrane, or the insertion of wedge-shaped hydrophobic helices into the membrane. A recent paper shows a third mechanism that can drive membrane curvature. Stachowiak and colleagues found that protein-protein crowding drives membrane bending. Protein coverage at 20% is sufficient to drive curvature, by creating lateral pressure of membrane-bound proteins colliding. Interestingly, even proteins unrelated to membrane curvature can induce curvature when overcrowded (GFP, for example). The cartoons and images above show vesicles that contain low (left) or high (right) levels of protein binding at specific domains at the membrane. High levels of protein caused membrane curvature, as seen as long lipid tubules.

Stachowiak JC, Schmid EM, Ryan CJ, Ann HS, Sasaki DY, Sherman MB, Geissler PL, Fletcher DA, & Hayden CC (2012). Membrane bending by protein-protein crowding. Nature cell biology, 14 (9), 944-9 PMID: 22902598 
Adapted by permission from Macmillan Publishers Ltd, copyright ©2012