Apoptosis is regulated by BCL-2 family proteins. Anti-apoptotic members suppress cell death by deploying a surface groove to capture the critical BH3 α-helix of pro-apoptotic members. Cancer cells hijack this mechanism by overexpressing anti-apoptotic BCL-2 family proteins to enforce cellular immortality. We previously identified and harnessed a unique cysteine (C55) in the groove of anti-apoptotic BFL-1 to selectively neutralize its oncogenic activity using a covalent stapled-peptide inhibitor. Here, we find that disulfide bonding between a native cysteine pair at the groove (C55) and C-terminal α9 helix (C175) of BFL-1 operates as a redox switch to control the accessibility of the anti-apoptotic pocket. Reducing the C55–C175 disulfide triggers α9 release, which promotes mitochondrial translocation, groove exposure for BH3 interaction and inhibition of mitochondrial permeabilization by pro-apoptotic BAX. C55–C175 disulfide formation in an oxidative cellular environment abrogates the ability of BFL-1 to bind BH3 domains. Thus, we identify a mechanism of conformational control of BFL-1 by an intramolecular redox switch.

细胞凋亡受 BCL-2 家族蛋白的调节。抗凋亡成员通过部署表面凹槽来捕获促凋亡成员的关键 BH3 α-螺旋来抑制细胞死亡。癌细胞通过过度表达抗凋亡 BCL-2 家族蛋白来劫持这种机制，以强制细胞永生。我们之前在抗凋亡 BFL-1 的凹槽中鉴定并利用了一种独特的半胱氨酸 (C55)，以使用共价钉肽抑制剂选择性地中和其致癌活性。在这里，我们发现凹槽 (C55) 处的天然半胱氨酸对与 BFL-1 的 C 末端 α9 螺旋 (C175) 之间的二硫键作为氧化还原开关来控制抗凋亡口袋的可及性。减少 C55–C175 二硫键会触发 α9 释放，从而促进线粒体易位，BH3相互作用的凹槽暴露和促凋亡BAX对线粒体通透性的抑制。在氧化细胞环境中形成 C55–C175 二硫键消除了 BFL-1 结合 BH3 结构域的能力。因此，我们通过分子内氧化还原开关确定了 BFL-1 构象控制的机制。