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Updated: May 27, 2026

Examining BCL-2 Family Function with Large Unilamellar Vesicles
Published on: October 5, 2012
Membrane binding by tBid initiates an ordered series of events culminating in membrane permeabilization by Bax
Jonathan F Lovell1, Lieven P Billen, Scott Bindner
1Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario L8N 3Z5, Canada.
Abstract:
In normal circumstances, the Bcl-2 family dutifully governs when cells die. However, the rules of engagement between the pro- and antiapoptotic family members are still contested, and how Bax is transformed from a cytosolic monomer to an outer mitochondrial membrane-permeabilizing oligomer is unclear. With fluorescence techniques and an in vitro system, the combination of tBid and Bax produced dramatic membrane permeabilization. The membrane is not a passive partner in this process beause membranes are required for the protein-protein interactions to occur. Simultaneous measurements of these interactions revealed an ordered series of steps required for outer membrane permeabilization: (1) tBid rapidly binds to membranes, where (2) tBid interacts with Bax, causing (3) Bax insertion into membranes and (4) oligomerization, culminating in (5) membrane permeabilization. Bcl-XL prevents membrane-bound tBid from binding Bax. Bad releases tBid from Bcl-XL, restoring both tBid binding to Bax and membrane permeabilization.
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