Figure 1.

Physicochemical properties that determine the rate of lipid transport were assessed for a variety of lipid chemistries and phases by calculating the free energy barriers for lipid desorption and insertion. (A) An illustrative free energy profile, calculated as a function of the reaction coordinate, r_LxS, for an L_α phase DMPC membrane, reveals barriers for lipid desorption (ΔF_des) and lipid insertion (ΔF_ins). Representative configurations are shown for negative values of r_LxS (at which the lipid is in solution) and for positive values of r_LxS (at which the lipid is in the membrane). Solvent is not rendered. (B) r_LxS is a linear combination of min(d_CC) (the minimal distance between any hydrophobic carbon of the lipid and of the closest membrane leaflet) and n_CC (the number of close hydrophobic carbon contacts between the lipid and closest leaflet). (C and D) Chemical structures of the lipids investigated with varied (C) acyl chain lengths and degrees of saturation and (D) headgroups. POPC’s structure is shown in both (C) and (D). In (C), hydrophobic carbons are boxed. (E) Representative configurations of membranes composed of DMPC, DPPC, or DSPC in both L_α and L_β phases. To see this figure in color, go online.