Cell biology is all about trying to find out how the cellular processes taking place in your body actually work. Unfortunately, we can’t just open up your body and look inside to see what’s happening (we would never get the ethics approval!). Instead, we often work with cells growing in plastic dishes and do our best to extract as much relevant information as possible from our experiments. We have to rely on artificial systems to test our hypotheses and often have to come up with original set-ups to investigate specific problems.
One of these creative inventions is the use of supported lipid bilayers—artificial membranes that can mimic biological cell membranes in a very controlled manner.
What are supported lipid bilayers?
Supported lipid bilayers (or bilayers for short) consist of two monolayers of lipids deposited onto a flat substrate such as a glass coverslip. The lipids consist of a hydrophilic lipidic tail (oriented inwards into the bilayer) and a charged hydrophobic head (facing outward). Importantly for your experiments, they look exactly like cell membrane bilayers, except that they are flat and that you can precisely control their lipid composition and protein content.
Why are bilayers useful?
That all sounds quite fancy, but why would you ever want to use artificial bilayers rather than directly study cellular membranes? There are quite a few examples where bilayers come in as a rather handy tool, primarily for microscopists:
Based on my own area of research, the first example that springs to mind is the study of the immunological synapse—in other words, investigating what’s going on when an immune cell (like a T cell or an NK cell) interacts with a target cell. Even with the high-tech microscopes available today, it is really difficult to study cell-cell interactions at high resolution because of the orientation of the cells (they can be facing in any direction) and the depth at which you have to image (even if one cell was conveniently sitting right on top of the other). On the other hand, if a cell lands on a flat lipid bilayer, it becomes really easy to observe protein interactions at the cell-bilayer interface, even by confocal microscopy.
It becomes even more interesting when you start manipulating the proteins present on the bilayers. You can control both the protein composition and concentration on your bilayers, thereby mimicking different cell-cell interactions. Using bilayers, a large number of cells can be analyzed in parallel.
Bilayers have been crucial for immunologists since the 90’s 1, but they are useful in other fields too, for studying:
- Cell adhesion
- Cell migration
- Membrane protein dynamics and interactions
- Lipid dynamics
- Receptor-ligand interactions
- Membrane fusion
In fact, whenever cell membranes are mentioned, you could probably learn something useful using supported lipid bilayers—without the complications of the cellular environment.
- Grakoui, A. et al. 1999. The Immunological Synapse: A Molecular Machine Controlling T Cell Activation. Science. 285, 221–227.