Reconciling Differences between Lipid Transfer in Free-Standing and Solid Supported Membranes: A Time-Resolved...

Area of Science:

• Membrane biophysics
• Lipid dynamics
• Cellular energetics

Background:

• Maintaining lipid gradients across cell membranes is vital for biological functions.
• Lipid transport rates in membranes exhibit significant variability, necessitating identification of experimental biases.
• Intramembrane transport rates of dimyristoylphosphatidylcholine (DMPC) differ between supported and free-standing membranes.

Purpose of the Study:

• To investigate the factors contributing to differing intramembrane transport rates of DMPC.
• To differentiate the effects of membrane curvature versus substrate support on lipid transport.
• To elucidate the mechanism behind fast lipid flip-flop in supported membranes.

Main Methods:

• Utilized DMPC vesicles and DMPC-supported membranes on silica nanoparticles of varying radii.
• Measured and compared lipid exchange and flip-flop rates in different membrane configurations.
• Analyzed activation energies for lipid exchange and melting temperature behavior.

Main Results:

• Membrane curvature (30 nm to 100 nm diameter) had minimal impact on DMPC transport rates.
• Lipid exchange rates in supported membranes were comparable to those in free-standing vesicles.
• DMPC flip-flop rates were significantly higher in supported membranes, even in defect-free systems, driven by surface-induced disorder.

Conclusions:

• The presence of a solid support, not membrane curvature, is the primary factor influencing fast lipid flip-flop rates.
• Surface-induced disorder in supported membranes enhances lipid acyl chain mobility, driving rapid flip-flop.
• Understanding these dynamics is crucial for accurately assessing the energetic costs of maintaining membrane lipid gradients.