Inhibition of Oligomeric BAX by an Anti-Apoptotic Dimer

BAX is a pro-apoptotic BCL-2 protein that resides in the cytosol as a monomer until triggered by cellular stress to transform into an oligomer that permeabilizes the mitochondria and induces apoptosis. We previously reported the generation of a full-length BAX oligomer (BAXO) that recapitulates pro-apoptotic functionality. Here, we find that full-length BCL-w can be induced to form a symmetric dimer (BCL-wD) that dissociates BAXO, inhibits its mitochondrial translocation, induces its retrotranslocation, and thereby blocks its membrane-porating activity. Structure-function analyses revealed discrete conformational changes upon BCL-w dimerization and reciprocal structural impacts upon BCL-wD and BAXO interaction. SAXS analysis demonstrated that BAXO forms pores by inducing negative Gaussian membrane curvature, which is reversed by positive Gaussian curvature exerted by BCL-wD. Our studies reveal an additional mechanism of apoptotic regulation mediated by the protein and membrane interactions of higher-order BCL-2 family multimers, redefining the “point of no return” for BAX-mediated apoptosis.BAX是一种促凋亡BCL-2蛋白（BCL-2 protein），以单体形式驻留于细胞质中，直至受到细胞应激触发，转变为可诱导线粒体膜通透并引发细胞凋亡的寡聚体。本团队此前已成功构建可重现促凋亡功能的全长BAX寡聚体（BAXO）。本研究发现，全长BCL-w可被诱导形成对称二聚体（BCL-wD），该二聚体能够解离BAXO、抑制其线粒体转位、诱导其逆向转位，进而阻断其膜成孔活性。结构-功能分析揭示了BCL-w二聚化后发生的特异性构象变化，以及BCL-wD与BAXO相互作用时双方产生的相互结构影响。小角X射线散射（SAXS）分析表明，BAXO通过诱导负高斯膜曲率形成孔道，而BCL-wD所施加的正高斯曲率可逆转这一过程。本研究揭示了由高阶BCL-2家族多聚体的蛋白质与膜相互作用所介导的凋亡调控新机制，重新定义了BAX介导的细胞凋亡的"point of no return"。