Effect of ergosterol or cholesterol on the morphology and dynamics of the POPC/sphingomyelin bilayer

Phase segregation and domain formation in cell membranes and model lipid bilayers have become a relevant topic in the last decades due to their role in important cell functions such as signaling and molecule-membrane interactions. To date, the most accepted explanation for the formation of these domains in mammalian cells is that cholesterol-enriched sphingomyelin patches of membrane form because of the preferential interaction between them. However, detailed information on molecular interactions within cholesterol-containing bilayers and their comparison with other sterol-containing bilayers, such as those containing ergosterol, is needed to understand the role these molecules have. Recent experimental findings have shown sterol-dependent differences in the morphology of supported lipid bilayers, but the molecular basis for these differences remains unclear. This work provides a molecular explanation for these differences using atomistic Molecular Dynamics simulations of lipid bilayers composed of 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) and N-palmitoyl-D-erythro-sphingosylphosphorylcholine (PSM) with 20 mol% of cholesterol or ergosterol. Atomic force microscopy was used to validate the simulation. The simulation ran for 11 mu s and revealed that both sterols affect the morphology of the membrane. Key findings include: ergosterol induces greater order in PSM domains compared to cholesterol, lipid diffusion constants are lower in ergosterol-containing membranes, sterol flip-flop rates are significantly reduced in ergosterol-containing membranes and ergosterol leads to greater PSM-sterol enrichment. These molecular-level differences provide insight into the experimentally observed variations in domain formation and membrane properties between cholesterol and ergosterol-containing bilayers. Our findings contribute to the understanding of sterol-specific effects on membrane organization and dynamics, with potential implications for cellular processes and drug interactions in different organisms. Statement of significance: This study advances our understanding of how different sterols influence membrane properties through molecular dynamics simulations of three-component lipid membranes. Specifically, we investigate the effects of two major sterols: ergosterol, predominantly found in plants and fungi, and cholesterol, characteristic of mammalian cells. While extensive research has elucidated cholesterol's impact on lipid bilayers, studies on ergosterol's effects are comparatively limited. Our work provides a comprehensive comparison of these sterols, highlighting their similarities and differences. These insights not only enhance our knowledge of cell membrane structure and function, but also contribute to our understanding of selective drug permeability across membranes. This research has potential implications for both fundamental cell biology and pharmaceutical applications.