Stabilization of the Raft Bilayer Structure due to Elastic Deformations of the Membrane

Line tension of the boundary of specific domains rich in sphingomyelin has been calculated. The calculations were based on the macroscopic theory of elasticity under the assumption that the raft bilayer is thicker than the bilayer of the surrounding membrane. The possibility of lateral shift of the domain boundaries located in different monolayers of the membrane was taken into account. The line tension was associated with the energy of elastic deformations arising in the vicinity of the boundary and compensating for the difference of the monolayer thickness. Spatial distribution of deformations and the line tension was calculated by minimization of elastic free energy of the system. The dependence of the line tension on the distance between the domains boundaries located in different monolayers was obtained. It was shown that the line tension is minimal at the distance of about 4 nm. Thus, membrane deformations stabilize the bilayer structure of rafts observed experimentally The calculated value of line tension is about 0.6 pN for the difference of the monolayer thickness of raft and surrounding membrane of about 0.5 nm, which is in agreement with the available experimental data.