Quantitative Characterization of Cholesterol Partitioning between Binary Bilayers.

We have devised a practical simulation protocol for quantitative characterization of cholesterol (Chol) partitioning between bilayers with different lipid types. The simulation model contains two patches of laterally contacting lipid bilayers, where the host lipids of each bilayer are allowed to self-adjust their packing. For two combinations of bilayers with different lipid types, 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC)/1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine (POPC) and 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC), the simulation model has been verified by self-adjusted lipid packing in each bilayer, convergence of Chol partitioning between different Chol initial distributions, and relative diffusion coefficients consistent to those from experiments. The calculated Chol partition coefficient between POPC and DOPC bilayers from the Chol partitioning simulations in the POPC-DPPC and DOPC-DPPC binary bilayer systems shows an excellent agreement with that from available Chol exchange experiments between 1-stearoyl-2-oleoyl- sn-glycero-3-phosphocholine(SOPC)/DOPC vesicles and β-cyclodextrins, which further validates the simulation protocol and illustrates its applicability to any molecular partitioning in the binary bilayer system.