Thermodynamics of lipid interactions in complex bilayers

Abstract

The mutual interactions between lipids in bilayers are reviewed, including mixtures of phospholipids, and mixtures of phospholipids and cholesterol (Chol). Binary mixtures and ternary mixtures are considered, with special emphasis on membranes containing Chol, an ordered phospholipid, and a disordered phospholipid. Typically the ordered phospholipid is a sphingomyelin (SM) or a long-chain saturated phosphatidylcholine (PC), both of which have high phase transitions temperatures; the disordered phospholipid is 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) or dioleoylphosphatidylcholine (DOPC). The unlike nearest-neighbor interaction free energies (omega(AB)) between lipids (including Chol), obtained by an variety of unrelated methods, are typically in the range of 0-400 cal/mol in absolute value. Most are positive, meaning that the interaction is unfavorable, but some are negative, meaning it is favorable. It is of special interest that favorable interactions occur mainly between ordered phospholipids and Chol. The interpretation of domain formation in complex mixtures of Chol and phospholipids in terms of phase separation or condensed complexes is discussed in the light of the values of lipid mutual interactions.

Understanding the Phase Behavior of Coarse-Grained Model Lipid Bilayers through Computational Calorimetry

“…35 This parameter can be optimized to reproduce the experimentally observed heat capacity curve. 36 There exist a host of refinements to this lattice-based approach, allowing for the description of the pretransition and the main transition as well as many-component bilayers. 37,38 In developing these models, the existence of both "gel-like" and "liquid-like" lipids is a specified feature rather than a consequence of lower-level molecular features.…”

Characterization of Solid-Supported Dipalmitoylphosphatidylcholine Membranes Containing Cholesterol

“…Cholesterol's ubiquitousness underlines its important role in altering the physical 1, 2 and thermodynamic properties of membranes by changing the packing or the ordering of lipids, reducing membrane permeability 3,4,5 , and in the formation of lipid rafts 6,7,8,9,10 . In particular, cholesterol is known to have a condensing effect on fluid phase lipids and to conversely fluidize solid phase lipids which helps maintain the integrity of cell membrane when stressed.…”

Pair interactions among ternary DPPC/POPC/cholesterol mixtures in liquid-ordered and liquid-disordered phases

“…While the l o state has been considered as a good working model for lipid rafts, the l d state mimics well the fluid, liquid crystalline phase of lipid membranes 3,4 . Study of the interactions of lipid-lipid and cholesterollipid in both l d and l o phases is important for further understanding of cell membranes 5,6 .…”