Water channel formation and ion transport in linear and branched lipid bilayers.

Using molecular dynamics simulations, we studied the influence of methyl chain branching on transmembrane potential induced formation of water channels in lipid bilayers and ion transport. We compared the response of a bilayer lipid that has multiple methyl branches diphytanoylphosphatidylcholine (DPhPC) with its straight-chain counterpart dipalmitoylphosphatidylcholine (DPPC) to a transmembrane potential created by an imbalance in ionic charges across the membrane. We found that, compared to the straight-chain DPPC lipid bilayer membranes, branched DPhPC lipid membranes require a higher critical transmembrane potential to break down, followed by water channel formation, and transport of anions and cations through the pore. We demonstrated that the bulkiness of the added methyl branches leads to "barrel-stave" pores in DPhPC membranes which require a higher transmembrane potential to produce than the toroidal pores produced in the straight chain DPPC lipid bilayers. Our results provided a deeper understanding of the water channel formation and ion transport through lipid bilayer membrane and might help explain the increased resistance to charge-induced poration in organisms with membranes abundant in branched lipids.