Lipid Interactions and Organization in Complex Bilayer Membranes.

Area of Science:

• Membrane biophysics
• Lipid self-assembly
• Materials science

Background:

• Bilayer lipid properties significantly influence membrane lateral structure, though these relationships are not fully understood.
• Model membrane studies indicate potential segregation of phospholipids (PLs) with varying melting points, especially when cholesterol is present.
• The impact of different phospholipid headgroups on bilayer lateral structure remains unclear.

Purpose of the Study:

• To investigate the formation of lateral heterogeneity in increasingly complex multilamellar bilayers, up to five components.
• To elucidate the role of phospholipid headgroup structure and cholesterol in modulating membrane lateral organization.
• To determine how acyl chain order and thermostability are affected by lipid composition and temperature.

Main Methods:

• Utilized time-resolved fluorescence spectroscopy with domain-selective fluorescent probes (PL-conjugated trans-parinaric acid).
• Employed (2)H Nuclear Magnetic Resonance (NMR) spectroscopy with site- or perdeuterated PLs.
• Measured changes in bilayer order as a function of temperature and lipid composition.

Main Results:

• In ternary bilayers, phospholipid headgroup structure (phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine) did not significantly alter acyl chain order or thermostability in sphingomyelin-rich domains.
• In complex five-component bilayers, no major differences were observed among monounsaturated PLs regarding cholesterol-induced ordering.
• Cholesterol demonstrated a preferential interaction with N-palmitoyl sphingomyelin compared to other deuterated PLs.

Conclusions:

• Complex five-component membranes exhibit lateral heterogeneity, particularly at lower temperatures.
• Cholesterol's influence on membrane structure is selective, favoring sphingomyelin.
• Phospholipid headgroup structure plays a minor role in acyl chain order within sphingomyelin-rich domains in these complex systems.