Figure 3.

Bax activation and oligomerization. (A) Asymmetric autoactivation of Bax. Membrane-embedded tBid interacts through its BH3 domain with Bax at its rear pocket (Step 1). This results not only in the exposure of the Bax carboxy-terminal helix, but also in the exposure of the BH3 domain of Bax (Step 2). According to the asymmetric autoactivation model, the exposed BH3 domain of Bax can recruit further Bax molecules to the OMM (Step 3) and activate them (Step 4). (B) Symmetric dimer formation causes Bax oligomerization. Activated Bax, which exposes its BH3 domain, forms symmetric dimers by a reciprocal interaction of one molecule’s BH3 domain with the hydrophobic groove of another, and vice versa (Step 1). Bax dimers can then form higher-order oligomers through another symmetric interaction involving the α-helices 6 at the surface opposite from the BH3–groove interaction (Step 2).