Modelling natural cell membranes and how lipid asymmetry influences structure

Cell membranes are integral to the structure and function of the cell for all organisms and have a complex mixture of lipids that vary between cellular organelles and between leaflets of a membrane. With improved lipidomic and selective labeling experimental studies, computational modeling of realistic cell membranes has been feasible . In this presentation, a summary of various models of cell membranes will be presented ranging from simple bacteria to those found in mammals. The outer membrane of gram-negative bacteria has extreme leaflet asymmetry with lipopolysaccharides in the outer leaflet. Even the inner membrane has charge asymmetry that yields varied membrane properties in thickness, lipid packing and elastic tilt modulus. Considering plants, the plasma membrane of Arabidopsis thaliana has an enriched outer leaflet with sterols and glycolipids. The outer leaflet tends to be more rigid with the formation of clusters induced by sterol-glycolipid interaction. Sterols play an important role to the structure and dynamics of mammalian membranes. Diabetic patients tend to have a lower concentration of cholesterol and unsaturated fatty acids in the peripheral myelin sheath that yield a more fluid and thinner membrane. For the ocular lens, the cholesterol concentration in these layered membranes of the lens is at least 50% and the levels depend on age and presence of cataracts. Lens of older patients and those with cataracts have higher acyl chain order, lower lipid diffusion and increased lateral structures of lipids. Finally, models for the phases present the lipid matrix of the stratum corneum were developed and based on the asymmetric partitioning of cholesterol in the multilayered structure of the long periodicity phase. Our simulations resulted in some ceramide lipids with extended acyl chains between layers and permeation estimates that matched that in natural skin.