Abstract:

Investigation of the thermodynamics of fatty acid (FA) modulation of lipid membrane behavior is important to understand the mechanisms that occur in cells. Previous research of the interaction between FAs and lipid membranes has been performed in dilute solution, and no study has focused on the effect of an external crowding medium on the phase transition of the lipid membrane induced by FAs. In this paper, the effect of various molecular weights and concentrations of polyethylene glycol (PEG) on the phase transition of 1, 2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) vesicles mixed with FA was systematically investigated by differential scanning calorimetry (DSC). The results show that the effect of PEG on the phase transition of pure DMPC vesicles is both molecular weight and concentration dependent. The presence of PEG significantly changes the phase transition of FA/DMPC vesicles. Phase transition temperature (T_m) of FA/DMPC vesicles increased in PEG for most of the considered concentrations and molecular weights. The original T_m of DMPC induced by short-chain saturated FA or unsaturated FA increased in the presence of PEG. Further investigation revealed that in most cases a collaborative effect of molecular crowding existed and the effect of PEG on T_m was both molecular weight and concentration dependent. Moreover, the cooperative unit (CU) of pure DMPC vesicles and most FA/DMPC systems decreased with increasing PEG concentration, indicating that the crowded medium contributes to the heterogeneity of the bilayers and that fewer molecules cooperatively participate in the phase transition. The results suggest that crowded media might repair disturbed membranes, which should not be ignored in the FA-modulating membrane related area.

Key words: Macromolecular crowding, Phospholipid vesicle, Fatty acid, Phase transition, Differential scanning calorimetry