Pattern formation in adhering lipid membranes

The cell membrane is the interface where the cell meets the outside world. Many essential biological processes (such as cell adhesion, endo- and exo-cytosis, and membrane fusion) involve either direct or protein-mediated adhesion of this membrane to another membrane, food, or another substance in the environment. Indeed, for many normative eukaryotic cells, adhesion to a substrate is essential for viability; corresponding cells that lack this requirement are often cancerous.

This project started with the intention of developing a reductionist model system that could elucidate the influence of physical factors in the response of the cell membrane to cell adhesion.  For this model system, we combined protein-mediated adhesion with a membrane made of a mixture of lipids and cholesterol that was near a demixing transition.

To our surprise, we found that proteins stabilized long-lived holes in the membranes.  This was unexpected because typically lipid membranes are very fragile to poration, and a pore of sufficient size will cause the membrane to lyse and disappear into sub-microscopic fragments.  We also learned that a combination of tension-induced pore formation and the dynamics of protein motion in the membrane can give rise to a striking fingering pattern in the membrane.  This work was on the cover of Langmuir!

Journal Cover

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This work was led by Orrin Shindell, who did his Ph.D. in Physics at UT Austin in the Gordon lab and is now on the faculty at Trinity University in San Antonio, Texas.