Lipid rafts
Lipid raft relative stiffness
Lipid rafts are cell membrane sub-microdomains enriched in cholesterol and in sphingolipids. Some proteins can specifically partition or be excluded from these domains. Rafts are important for signal transduction, but are also used by pathogens to penetrate the cell.
Rafts have a different lipid composition and structure than the surrounding membrane. Moreover, the protein diffusion in the membrane decrease drastically when located into rafts. The question is then does lipid raft have different stiffness properties than the surrounding membrane
We answered this question with AFM, using the force spectrosopy mode. Lipid rafts were localized by looking at GPI-anchored proteins, known to partition into the rafts. In order to get rid of large scale stiffness variation, we computed the relative stiffness, where we compare the stiffness of lipid raft to the stiffness of the surrounding membrane at different distances.
The conclusion of our study was that lipid rafts are 30 % stiffer than the surrounding membrane, and that their size is below 70 nm.
This study was published in the Biophyslcal Journal.