Micron-sized domains in quasi single-component giant vesicles

Area of Science:

• Membrane biophysics
• Cell biology
• Lipid self-assembly

Background:

• Giant unilamellar vesicles (GUVs) are crucial model membranes for studying membrane biophysics and cell biology.
• Investigating lipid phase transitions and domain formation in GUVs often involves standard preparation protocols using sugar solutions.
• These standard methods may inadvertently introduce artifacts affecting membrane behavior.

Purpose of the Study:

• To investigate the impact of standard giant unilamellar vesicle preparation protocols on membrane heterogeneity.
• To identify the source and mechanism of artifactual domain formation in GUVs.
• To develop strategies for mitigating these preparation-induced artifacts.

Main Methods:

• Preparation of giant unilamellar vesicles (GUVs) from single phospholipids using standard sugar solutions.
• Visualization of membrane heterogeneity using a fluorescent lipid dye (0.1 mol%).
• Observation of GUVs under varying temperatures, particularly around the main phase transition temperature (T_M).
• Testing the effect of supplementing sugar solutions with nanometer-sized liposomes.

Main Results:

• Standard GUV preparation with glucose led to the abnormal formation of micron-sized, dye-depleted domains in single-component lipid vesicles.
• These domains nucleated approximately 10 K above the lipid main phase transition temperature (T_M).
• Stripe-like, dye-enriched structures were observed near T_M, while dye-depleted domains appeared to originate from glucose impurities.
• Supplementing glucose with liposomes suppressed the formation of these artifactual domains.

Conclusions:

• Traces of impurities in sugar solutions, particularly glucose, can induce micron-sized domains in GUVs, mimicking true phase separation.
• These impurities can significantly alter perceived lipid phase diagrams, leading to discrepancies in research findings.
• Using liposomes during GUV preparation can effectively sequester impurities and prevent artifactual domain formation.