Anionic lipid domains: correlation with functional topography in a mammalian cell membrane

Area of Science:

• Cell Biology
• Biochemistry
• Membrane Biophysics

Background:

• Anionic phospholipids are crucial for cell membrane structure and function.
• Understanding their distribution in sperm plasma membranes is vital for reproductive biology.
• Polymyxin B is a known antibiotic that interacts with anionic lipids.

Purpose of the Study:

• To investigate the distribution of anionic phospholipids in sperm plasma membranes using Polymyxin B.
• To examine the effects of Polymyxin B on various cell membrane models and sperm cells.
• To correlate membrane disruption patterns with specific functional domains in sperm.

Main Methods:

• Electron microscopy of freeze-fracture replicas to visualize membrane structures.
• Liposome assays with phosphatidylcholine and phosphatidylethanolamine to assess Polymyxin B interaction.
• Fluorescence microscopy using a dansylated Polymyxin B derivative for lipid binding detection.
• Application of Polymyxin B to Drosophila larval cell membranes and guinea pig sperm cells.

Main Results:

• Polymyxin B did not perturb phosphatidylcholine liposomes but disrupted phosphatidylethanolamine-containing liposomes.
• Both Drosophila larval cell membranes and guinea pig sperm membranes were disrupted by Polymyxin B.
• Specific sperm membrane domains exhibited distinct responses: fusional domains showed protrusions, flagellum membrane showed bubbling, while particle arrays and postacrosomal segments remained smooth.
• Heterogeneous binding of the dansylated Polymyxin B derivative was observed via fluorescence microscopy.

Conclusions:

• Polymyxin B effectively probes the distribution of anionic phospholipids in sperm plasma membranes.
• The heterogeneous distribution of anionic lipids correlates with functional specialization of sperm membrane domains.
• Polymyxin B serves as a valuable tool for studying membrane lipid organization and its functional implications.