Detergent-activated BAX protein is a monomer.

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• BAX, a pro-apoptotic protein in the BCL-2 family, is crucial for initiating programmed cell death.
• BAX activation involves translocation to the outer mitochondrial membrane and pore formation, a process with debated mechanisms.
• In vitro studies suggest BAX oligomerizes during detergent activation, contrasting with in vivo findings of monomeric insertion.

Purpose of the Study:

• To investigate the molecular mechanism of BAX activation by detergents.
• To determine the oligomeric state of BAX during detergent interaction.
• To reconcile conflicting in vitro and in vivo models of BAX activation.

Main Methods:

• Utilized single-molecule sensitivity techniques: fluorescence correlation spectroscopy (FCS) and fluorescence-intensity distribution analysis (FIDA).
• Examined BAX interaction with various detergents: n-octyl glucoside, dodecyl maltoside, Triton X-100, Tween 20, CHAPS, and cholic acid.
• Simultaneously measured molecular weight and protein stoichiometry within BAX-detergent complexes.

Main Results:

• BAX consistently exists as a monomer before, during, and after interaction with detergent micelles.
• Observed no evidence of BAX oligomerization during detergent-mediated activation across tested detergents.
• Demonstrated that detergent activation does not involve BAX oligomerization.

Conclusions:

• Detergent activation of BAX does not lead to oligomerization, contrary to previous hypotheses.
• BAX can adopt two distinct, stable monomeric conformations under physiologic conditions: an inactive and an active state.
• The findings suggest a revised model for BAX activation, emphasizing monomeric conformational changes over oligomerization during detergent interaction.