Coarse-grained molecular simulations of membrane adhesion domains

Abstract

We use a coarse-grained molecular model of supported lipid bilayers to study the formation of adhesion domains. We find that this process is a first order phase transition, triggered by a combination of pairwise short range attractive interactions between the adhesion bonds and many-body Casimir-like interactions, mediated by the membrane thermal undulations. The simulation results display an excellent agreement with the recently proposed Weil-Farago two-dimensional lattice model, in which the occupied and empty sites represent, respectively, the adhesion bonds and unbound segments of the membrane. A second phase transition, into a hexatic phase, is observed when the attraction between the adhesion bonds is further strengthened.

Formation of adhesion domains in stressed and confined membranes

“…In one such study, we simulated a bilayer membrane with a small fraction of lipids from the lower monolayer connected to an underlying surface, and additionally introduced a short range attractive potential of depth e between the adhesive lipids. 20 Our simulations revealed that the adhesive lipids underwent a first order condensation transition when the strength of the short range potential between them exceeds a threshold value of e c 4 0. The fact that adhesion domains do not form when e = 0 implies that the fluctuation entropy gained by the aggregation of the adhesive lipids only partially compensates for their loss of mixing entropy.…”

“…The details of the simulations can be found in ref. [20]. Briefly, we simulated bilayers of 2N = 2000 lipids (1000 lipids per monolayer), where each lipid consists of one hydrophilic (head) bead and two hydrophobic (tail) beads of size σ.…”

“…23 The details of the simulations can be found in ref. 20. Briefly, we simulated bilayers of 2N = 2000 lipids (1000 lipids per monolayer), where each lipid consists of one hydrophilic (head) bead and two hydrophobic (tail) beads of size s. A flat impenetrable surface was placed below the membrane at z = 0, and adhesion was established by connecting N b head beads from the lower monolayer to it.…”

“…A similar conclusion was recently reached in simulation studies employing coarse-grained (CG) molecular models, which provide a more physical description of the system. In one such study, we simulated a bilayer membrane with a small fraction of lipids from the lower monolayer connected to an underlying surface, and additionally introduced a short range attractive potential of depth ǫ between the adhesive lipids [20]. Our simulations revealed that the adhesive lipids underwent a first order condensation transition when the strength of the short range potential between them exceeds a threshold value ǫ c > 0.…”

Formation of semi-dilute adhesion domains driven by weak elasticity-mediated interactions

“…This prediction was later examined in several computational studies, which demonstrated that, indeed, the renormalized temperature is about third to half of the thermodynamic temperature. [22][23][24][25]. These findings highlight the important role of thermal fluctuations in facilitating conditions required to adhesion cluster formation.…”