The cytoskeletal protein actin polymerizes into filaments that are essential for the mechanical stability of mammalian cells. In vitro experiments showed that direct interactions between actin filaments and lipid bilayers are possible and that the net charge of the bilayer as well as the presence of divalent ions in the buffer play an important role. In vivo, colocalization of actin filaments and divalent ions are suppressed, and cells rely on linker proteins to connect the plasma membrane to the actin network. Little is known, however, about why this is the case and what microscopic interactions are important. A deeper understanding is highly beneficial, first, to obtain understanding in the biological design of cells and, second, as a possible basis for the building of artificial cortices for the stabilization of synthetic cells. Here, we report the results of coarse-grained molecular dynamics simulations of monomeric and filamentous actin in the vicinity of differently charged lipid bilayers. We observe that charges on the lipid head groups strongly determine the ability of actin to adsorb to the bilayer. The inclusion of divalent ions leads to a reversal of the binding affinity. Our in silico results are validated experimentally by reconstitution assays with actin on lipid bilayer membranes and provide a molecular-level understanding of the actin-membrane interaction.

Coarse-grained molecular dynamics simulations are employed to obtain a detailed view of the formation of long-range ordered lamellar structures of physisorbed self-assembling long functionalized alkanes on graphite. During the self-assembly, two processes take place: Langmuir preferential adsorption and rearrangement on the surface. The rearrangement starts with nucleation, in which molecules create an ordered domain. The nucleation mechanism is temperature dependent. At lower temperature independent, small and stable nuclei seed the emergence of long-range ordered domains. In contrast, at a higher temperature, molecules adsorb on the surface, and only when a certain level of surface coverage by the adsorbent is reached, the whole structure undergoes a transition from a liquid-like structure to an ordered structure. After this step, relatively slow corrections of the structure take place by Ostwald ripening.