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Model Plasma Membrane Exhibits a Microemulsion in Both Leaves Providing a Foundation for "Rafts"
David W Allender1, Ha Giang2, M Schick3
1Department of Physics, University of Washington, Seattle, Washington; Department of Physics, Kent State University, Kent, Ohio.
Biophysical Journal
|February 6, 2020
Summary
The plasma membrane exhibits nanoscale lipid domains with distinct compositions and curvatures, driven by lipid-curvature coupling. This organization arises from membrane properties and cytoskeleton interactions, revealing intrinsic plasma membrane structure.
Area of Science:
- Biophysics
- Cell Biology
- Materials Science
Background:
- Plasma membranes possess complex lipid compositions in their outer and inner leaflets.
- Lipid-protein interactions and membrane curvature influence membrane organization.
- Existing models do not fully explain the intrinsic nanoscale structure of disordered fluid membranes.
Purpose of the Study:
- To model the lipid organization and domain formation in a simplified plasma membrane.
- To investigate the coupling between local lipid composition and membrane curvature.
- To elucidate the origin of nanoscale structure in the plasma membrane.
Main Methods:
- Computational modeling of a two-leaflet lipid membrane.
- Incorporation of experimental lipid compositions for outer (sphingomyelin, phosphatidylcholine, cholesterol) and inner (phosphatidylethanolamine, phosphatidylserine, phosphatidylcholine, cholesterol) leaflets.
- Application of the Leibler-Andelman mechanism to couple composition fluctuations with curvature fluctuations.
Main Results:
- Structure factors revealed peaks at nonzero wavevectors, indicating characteristic nanoscale organization.
- The model predicts two distinct types of lipid domains with differing compositions and curvatures.
- Domain 1: Outer leaflet enriched in cholesterol and sphingomyelin; inner leaflet enriched in phosphatidylserine and phosphatidylcholine.
- Domain 2: Outer leaflet enriched in phosphatidylcholine; inner leaflet enriched in cholesterol and phosphatidylethanolamine.
Conclusions:
- The study provides a theoretical basis for the emergence of nanoscale lipid domains in the plasma membrane.
- Lipid-curvature coupling and membrane properties (bending modulus, surface tension) dictate the observed structure.
- The findings offer insights into the intricate organization of lipids within the plasma membrane.
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