Apoptosis is a central process in development, homeostasis, and tumor suppression, initiated by mitochondrial outer membrane permeabilization driven by the pore-forming protein Bax. While the pore-forming activity of Bax is well established, the molecular events that control its recruitment and activation at mitochondria remain incompletely understood. The mitochondrial porin VDAC2 has been proposed to mediate Bax translocation, but its role has not been defined at the molecular level. Here, we elucidate the molecular basis of Bax-VDAC2 interactions using an integrative strategy combining single-channel electrophysiology, purification of the complex, biophysical and structural characterization, and molecular dynamics simulations. We show that Bax binds specifically to VDAC2, but not to VDAC1, providing the first unequivocal evidence of VDAC isoform specificity. VDAC2 and Bax form a stable complex that induces long-lived channel blockages with reduced conductance. This interaction is mediated by insertion of the Bax C-terminal α9 helix into the β-barrel wall of VDAC2. Based on these data, we propose and validate a structural model of Bax-VDAC2 interaction that explains conformational activation of Bax at the mitochondrial membrane. Together, these findings establish VDAC2 as a dedicated Bax recruitment platform that promotes conformational activation and membrane insertion of Bax. By providing the first direct structural and functional characterization of the Bax-VDAC2 complex, this work improves our understanding of VDAC’s role in apoptosis regulation and opens new avenues for therapeutic strategies targeting Bax-dependent cell death in cancer and degenerative diseases.
Ravishankar et al. (2026) studied this question.