Curvature-Induced Lipid Sorting in Plasma Membrane Tethers

Abstract

Membrane tethers are nanotubes formed by lipid bilayers. They are efficient structures for cellular transport and communication, and for storage of excess membrane area. Previous tether pulling experiments provided insights on membrane mechanical properties, and the curvature effects on phase behaviour and distribution of coexisting phases. However, detailed information on tether properties and variations in composition is challenging to obtain experimentally due to the small diameters and dynamic nature of tethers.Here we provide a molecular view on curvature-induced lipid sorting in plasma membrane tethers. We pulled tethers from an idealized plasma membrane model using molecular dynamics simulations with the coarse-grained Martini model. The membrane consists of 63 lipid types with an asymmetric distribution of components between the leaflets [JACS, 2014, 136, 14554]. The tethers are formed by applying an external constant force to a lipid patch in the direction normal to the bilayer plane [Biophys J, 1012, 102, 1866]. Pulling is performed both from the inner and outer leaflets, corresponding to the direction in and out of the cell, respectively. As a result of pulling, we observe re-distribution of different lipid types along the regions of different curvature without macroscopic phase separation. Depending on the direction of pulling, the distribution of lipids and the tether properties differ.