Evidence for the formation of symmetric and asymmetric DLPC-DAPC lipid bilayer domains.

We investigated if mixtures of the phosphatidylcholine (PC) lipids 1,2-dilauroyl-sn-glycero-3-phosphocholine (C12:0 PC; DLPC) and 1,2-diarachidoyl-sn-glycero-3-phosphocholine (C20:0 PC; DAPC), which differ by eight methylene groups in acyl chain length, lead to the spontaneous formation of distinct lipid rafts and asymmetric bilayers. The experiments were performed using Atomic Force Microscopy (AFM). We show that DLPC and DAPC mixed at a molar ratio of 1:1 lead to the formation of single, double and triple bilayers with peaks at 6.14 ± 0.11, 13.27 ± 0.17 and 20.54 ± 0.46 nm, respectively (n=750). Within these formations discrete height steps of 0.92 nm can be resolved (n=422). The most frequently observed height steps value of 0.92 nm matches best with the calculated mean lipid hydrophobic thickness difference for asymmetric C12:0 PC and C20:0 PC lipid bilayers of 0.88 nm. This indicates the ability of DLPC and DAPC to form asymmetric lipid bilayers.