Mañas Adriana, Wang Sheng, Nelson Adam, Li Jiajun, Zhao Yu, Zhang Huaiyuan, Davis Aislinn, Xie Bingqing, Maltsev Natalia, Xiang Jialing
Department of Biology, Illinois Institute of Technology, Chicago, IL 60616, USA.
Human Genetics Department, Computation Institute, University of Chicago, Chicago, IL 60637, USA.
Exp Cell Res. 2017 Oct 15;359(2):342-355. doi: 10.1016/j.yexcr.2017.08.016. Epub 2017 Aug 12.
Bax∆2 is a functional pro-apoptotic Bax isoform having alterations in its N-terminus, but sharing the rest of its sequence with Baxα. Bax∆2 is unable to target mitochondria due to the loss of helix α1. Instead, it forms cytosolic aggregates and activates caspase 8. However, the functional domain(s) responsible for BaxΔ2 behavior have remained elusive. Here we show that disruption of helix α1 makes Baxα mimic the behavior of Bax∆2. However, the other alterations in the Bax∆2 N-terminus have no significant impact on aggregation or cell death. We found that the hallmark BH3 domain is necessary but not sufficient for aggregation-mediated cell death. We also noted that the core region shared by Baxα and Bax∆2 is required for the formation of large aggregates, which is essential for BaxΔ2 cytotoxicity. However, aggregation by itself is unable to trigger cell death without the C-terminus. Interestingly, the C-terminal helical conformation, not its primary sequence, appears to be critical for caspase 8 recruitment and activation. As Bax∆2 shares core and C-terminal sequences with most Bax isoforms, our results not only reveal a structural basis for Bax∆2-induced cell death, but also imply an intrinsic potential for aggregate-mediated caspase 8-dependent cell death in other Bax family members.
Bax∆2是一种具有促凋亡功能的Bax亚型，其N端存在改变，但其余序列与Baxα相同。由于α1螺旋的缺失，Bax∆2无法靶向线粒体。相反，它形成胞质聚集体并激活半胱天冬酶8。然而，负责BaxΔ2行为的功能域仍不清楚。在此我们表明，α1螺旋的破坏使Baxα模仿Bax∆2的行为。然而，Bax∆2 N端的其他改变对聚集或细胞死亡没有显著影响。我们发现标志性的BH3结构域对于聚集介导的细胞死亡是必要的，但并不充分。我们还注意到，Baxα和Bax∆2共有的核心区域对于形成大聚集体是必需的，这对于BaxΔ2的细胞毒性至关重要。然而，聚集体本身在没有C端的情况下无法触发细胞死亡。有趣的是，C端螺旋构象而非其一级序列，似乎对招募和激活半胱天冬酶8至关重要。由于Bax∆2与大多数Bax亚型共享核心和C端序列，我们的结果不仅揭示了Bax∆2诱导细胞死亡的结构基础，还暗示了其他Bax家族成员中存在聚集体介导的半胱天冬酶8依赖性细胞死亡的内在潜力。
