The substitution of Proline 168 favors Bax oligomerization and stimulates its interaction with LUVs and mitochondria.

Bax is a major player in the apoptotic process, being at the core of the mitochondria permeabilization events. In spite of the major recent advances in the knowledge of Bax organization within the membrane, the precise behavior of the C-terminal helix α9 remains elusive, since it was absent from the resolved structure of active Bax. The Proline 168 (P168) residue, located in the short loop between α8 and α9, has been the target of site-directed mutagenesis experiments, with conflicting results. We have produced and purified a recombinant mutant Bax-P168A, and we have compared its behavior with that of wild-type Bax in a series of tests on Large Unilamellar Vesicles (LUVs) and isolated mitochondria. We conclude that Bax-P168A had a greater ability to oligomerize and bind to membranes. Bax-P168A was not more efficient than wild-type Bax to permeabilize liposomes to small molecules but was more prone to release cytochrome c from mitochondria.