Lipid Structure and Composition Control Consequences of Interleaflet Coupling in Asymmetric Vesicles

Area of Science:

• Membrane biophysics
• Lipid self-assembly
• Physical chemistry

Background:

• Cell membranes exhibit lateral heterogeneity, with ordered domains (rafts) influencing protein function.
• Understanding lipid interactions in asymmetric bilayers is crucial for mimicking cellular membrane complexity.

Purpose of the Study:

• To investigate how inner leaflet composition affects outer leaflet lipid ordering in asymmetric vesicles.
• To determine the role of high-melting-temperature (high-Tm) phosphatidylcholine acyl-chain length and sphingomyelin content in modulating domain formation.

Main Methods:

• Förster resonance energy transfer (FRET) was used to assess liquid-ordered domain formation.
• Asymmetric vesicles with varying outer leaflet high-Tm lipids (saturated PCs or sphingomyelin) and inner leaflets (DOPC and cholesterol) were studied.
• Comparisons were made with symmetric vesicles of identical outer leaflet composition.

Main Results:

• Outer leaflet domain formation in asymmetric vesicles was sensitive to the acyl-chain length of high-Tm phosphatidylcholines.
• Short acyl-chain lipids (e.g., diC14:0PC) in the inner leaflet significantly inhibited outer leaflet domain formation, unlike in symmetric vesicles.
• Longer acyl-chain lipids (e.g., diC18:0PC) in the outer leaflet allowed domain formation independent of the inner leaflet.
• Decreasing sphingomyelin content in asymmetric vesicles led to greater inhibition of domain stability compared to symmetric vesicles.

Conclusions:

• Inner leaflet physical properties can dominate outer leaflet behavior in asymmetric lipid bilayers.
• The extent of this dominance is inversely related to the intrinsic ordering propensity of the outer leaflet lipids.
• These findings provide insights into the regulation of lipid domain formation in biological membranes.