tBid forms a pore in the liposome membrane

Area of Science:

• Biochemistry
• Membrane Biophysics
• Cell Biology

Background:

• The truncated form of Bid (tBid) is a key apoptotic protein.
• Understanding tBid's membrane interaction is crucial for apoptosis research.

Purpose of the Study:

• To investigate tBid's ability to permeabilize liposomes.
• To determine how phospholipid composition affects tBid-induced leakage.
• To elucidate the mechanism of tBid-mediated membrane disruption.

Main Methods:

• Large unilamellar vesicles (LUVs) were used to model cell membranes.
• Fluorescent marker molecules (FITC-dextrans) of various sizes were encapsulated in LUVs.
• Lipid composition effects on tBid-induced leakage were assessed using phospholipid monolayer assays and fluorescence quenching.

Main Results:

• tBid efficiently induced leakage of FITC-dextrans from LUVs.
• Leakage was most efficient in LUVs composed of cardiolipin and dioleoylphosphatidylcholine (DOPC).
• Increasing amounts of dioleoylphosphatidylethanolamine or dielaidoylphosphatidylethanolamine reduced leakage efficiency.
• tBid was found to insert deeply into the hydrophobic acyl chains of acidic phospholipids.

Conclusions:

• tBid permeabilizes liposomes in a lipid-composition-dependent manner.
• tBid's deep insertion into acidic phospholipids suggests a pore-forming mechanism.
• tBid likely penetrates the hydrophobic core of membranes, causing content leakage.