Probing DMPG vesicle surface with a cationic aqueous soluble spin label

Area of Science:

• Lipid bilayer biophysics
• Physical chemistry of membranes
• Spin labeling techniques

Background:

• Phase transitions in lipid bilayers are critical for membrane function.
• Previous studies suggested surface potential alterations accompany these transitions.
• Direct measurement of vesicle surface potential changes has been challenging.

Purpose of the Study:

• To directly monitor the surface potential of DMPG (dimyristoylphosphatidylglycerol) vesicles.
• To test the hypothesis that surface potential changes correlate with lipid phase transitions.
• To quantify DMPG surface potentials using a novel spin label.

Main Methods:

• Utilized a deuterated, cationic spin label (dCAT1) for direct surface monitoring.
• Analyzed temperature-dependent partitioning of dCAT1 between vesicle surface and aqueous phase.
• Estimated surface potentials using a two-site electrostatic model and ESR spectra.
• Compared experimental results with Gouy-Chapman-Stern model predictions.

Main Results:

• dCAT1 partitioning indicated an increased surface potential at the DMPG gel to liquid-crystal transition.
• Results support the hypothesis linking surface potential alterations to phase transitions.
• Surface potentials estimated from dCAT1 partition ratios aligned with Gouy-Chapman-Stern predictions.
• Observed phenomena at a higher temperature phase transition were less conclusive.

Conclusions:

• The study provides direct evidence for surface potential increases during DMPG lipid phase transitions.
• The deuterated cationic spin label (dCAT1) is effective for monitoring charged lipid vesicle surfaces.
• The findings support the role of electrostatic interactions in lipid membrane phase behavior.
• Further investigation is needed for less definitive phase transition observations.