Sterol chemical configuration and conformation influence the thermotropic phase behaviour of dipalmitoylphosphatidylcholine mixtures containing 5β-cholestan-3β- and -3α-ol.
We report here our differential scanning calorimetry measurements investigating the thermotropic phase behaviour of binary dipalmitoylphosphatidylcholine (DPPC)/sterol mixtures containing two saturated sterols with different ring configurations (5β-H and either 3α-OH or 3β-OH). These measurements differ in the proportions of sharp and broad components in the heating endotherms, representing the melting of the sterol-poor and sterol-rich lipid micro-domains of the DPPC bilayer, respectively. Our results suggest that the 5,10-cis ring configuration of both saturated sterols and the ring A conformations have the greatest influence on DPPC bilayer properties, most likely by inducing small increases in the mean area/molecule as compared to cholesterol. However, the C3-OH orientation also influences sterol miscibility, likely due to variations in the strength and number of interfacial H-bonds with changes in molecular area, which in turn probably reflect the depth of the sterol in the DPPC bilayer. This influence of C3-OH orientation is significantly greater than was observed in our earlier study of cholesterol/- and epicholesterol/DPPC mixtures. Overall, our results show that both saturated and unsaturated 3α-ols are less miscible than the corresponding 3β-ols, but that the presence of a Δ(5) double bond can improve the sterol miscibility in the DPPC bilayer at high sterol concentrations.
Department of Biochemistry, School of Molecular and Systems Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, Alberta, T6G 2H7, Canada.
Matthew G K
MG
Benesch
David A
DA
Mannock
Ronald N
RN
McElhaney
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D004083:Cholestanol / Q000737:chemistry*; D007536:Isomerism; D008051:Lipid Bilayers / Q000737:chemistry*; D008968:Molecular Conformation; D044367:Phase Transition; D013696:Temperature; D013816:Thermodynamics
D008051:Lipid Bilayers; D015060:1,2-Dipalmitoylphosphatidylcholine; D004083:Cholestanol