Single-molecule probes of lipid membrane structure

Area of Science:

• Biophysics
• Materials Science
• Molecular Biology

Background:

• Biological membranes exhibit heterogeneity crucial for organizing and modifying membrane constituents.
• Understanding membrane structure and organization is key to linking structural metrics with function.
• Single-molecule fluorescence microscopy offers a powerful tool for probing membrane structure at the molecular level.

Purpose of the Study:

• To measure membrane structure at the molecular level using single-molecule fluorescence studies.
• To investigate the orientation of fluorescent lipid analogs in lipid films.
• To correlate lipid orientation with changes in membrane packing and the effects of cholesterol.

Main Methods:

• Utilized polarized total internal reflection fluorescence microscopy with p-polarized excitation and spherical aberrations.
• Measured the orientation of BODIPY-PC and DiIC18 fluorescent lipid analogs in DPPC and arachidic acid Langmuir-Blodgett films.
• Analyzed the sensitivity of lipid orientation to surface pressure and the impact of cholesterol on DPPC monolayers.

Main Results:

• BODIPY-PC tailgroup orientation showed significant sensitivity to surface pressure in DPPC films, transitioning from in-plane to surface-normal orientation.
• DiIC18 headgroup orientation remained insensitive to surface pressure, consistent with its location.
• Single-molecule measurements revealed cholesterol-induced ordering in DPPC monolayers.

Conclusions:

• Single-molecule orientation measurements provide detailed insights into lipid packing and membrane heterogeneity.
• The location of the fluorophore significantly influences its sensitivity to changes in membrane packing.
• This technique is valuable for understanding how molecular-level structural changes impact biological membrane function.