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Correlation between lipid plane curvature and lipid chain order
M Lafleur1, M Bloom, E F Eikenberry
1Département de chimie, Université de Montréal, Québec, Canada. lafleur@ere.umontreal.ca
Biophysical Journal
|June 1, 1996
Summary
Investigating lipid phases with x-ray diffraction and NMR, this study reveals how temperature and composition affect membrane structure. A model correlates lipid chain order and headgroup area to predict phase behavior.
Area of Science:
- Membrane Biophysics and Lipid Self-Assembly
- Soft Matter Physics
- Structural Biology
Background:
- Phospholipids form diverse structures, including the inverted hexagonal (HII) phase, crucial for biological processes.
- Understanding the factors governing lipid phase transitions and structural parameters is essential for deciphering membrane function.
- The interplay between lipid composition, temperature, and additives like alkanes significantly influences lipid phase behavior.
Purpose of the Study:
- To investigate the structural and orientational properties of the 1-palmitoyl-2-oleoyl-phosphatidylethanolamine: 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPE:POPC) system in the HII phase.
- To elucidate the effects of dodecane, temperature, and POPE:POPC ratio on intercylinder spacing and acyl chain order.
- To develop and validate a geometrical model correlating lipid chain order and headgroup area with HII phase curvature.
Main Methods:
- X-ray diffraction was employed to measure intercylinder spacings in the HII phase.
- 2H nuclear magnetic resonance (NMR) spectroscopy was used to determine the orientational order of lipid acyl chains.
- A geometrical model was developed to predict HII phase intercylinder spacings based on experimental parameters.
Main Results:
- Dodecane addition induced the HII phase for POPE:POPC mixtures (0-39 mol% POPC) and slightly decreased chain order.
- Increased temperature or POPE proportion reduced intercylinder spacing, primarily by decreasing the water core radius.
- Temperature decreased acyl chain order, while POPE proportion had minimal effect; a correlation between curvature and chain order was observed.
Conclusions:
- A proposed geometrical model accurately predicts intercylinder spacings in the HII phase based on temperature and lipid composition.
- Temperature primarily influences HII phase curvature through hydrophobic core disorder, while POPC content affects the headgroup interface.
- Lipid chain order in the Lα phase reflects curvature frustration, with increased order correlating with pronounced curling tendencies.