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ABCG5/G8 Crystallization in a Lipidic Bicelle Environment for X-Ray Crystallography
Published on: August 25, 2023
Water diffusion in bicelles and the mixed bicelle model
Ronald Soong1, Peter M Macdonald
1Department of Chemistry, University of Toronto, Ontario, Canada L5L 1C6.
Langmuir : the ACS Journal of Surfaces and Colloids
|January 1, 2009
Summary
This study confirms the mixed bicelle model by measuring water diffusion using nuclear magnetic resonance (NMR). Water diffusion across bicelles depends on lipid composition, supporting DHPC miscibility within DMPC.
Area of Science:
- Biophysics
- Materials Science
- Physical Chemistry
Background:
- Bicelles are model membrane systems used to study lipid behavior.
- The mixed bicelle model proposes specific arrangements and dynamics of lipids within these structures.
- Understanding lipid miscibility and water diffusion is crucial for membrane biophysics.
Purpose of the Study:
- To validate the mixed bicelle model by examining water diffusion dynamics.
- To investigate the relationship between lipid composition and water transport across bicellar lamellae.
- To determine the structural implications of lipid miscibility within bicelles.
Main Methods:
- Stimulated echo (STE) pulsed field gradient (PFG) proton (1H) nuclear magnetic resonance (NMR) spectroscopy.
- (31)P NMR spectroscopy to analyze lipid exchange and populations.
- Magnetic alignment of bicelles (positively and negatively) composed of DHPC and DMPC mixtures.
- Variable temperature and varying DHPC proportion experiments.
Main Results:
- Water diffusion across bicellar lamellae scales with the fraction of edge vs. planar phospholipid (q*), not just the overall lipid ratio (q).
- Geometric modeling suggests DHPC-rich toroidal perforations have an upper size limit of 400 Å.
- (31)P NMR confirmed fast exchange of DHPC between curved and planar regions, supporting the mixed bicelle model.
Conclusions:
- The findings provide independent confirmation of the mixed bicelle model.
- DHPC exhibits finite miscibility with DMPC within the bicelle lamellae, rather than being confined to edges.
- Water diffusion is directly influenced by the specific arrangement and accessibility of lipids at the bicelle edges.
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