Annis Matthew G, Soucie Erinn L, Dlugosz Paulina J, Cruz-Aguado Jorge A, Penn Linda Z, Leber Brian, Andrews David W
Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario, Canada.
EMBO J. 2005 Jun 15;24(12):2096-103. doi: 10.1038/sj.emboj.7600675. Epub 2005 May 26.
Bax promotes cell death by permeabilizing mitochondrial outer membranes by an unresolved mechanism. However, in cells lacking the gene c-myc, membrane permeabilization by Bax is blocked by changes in the mitochondria that prevent Bax oligomerization. Drug-treated c-myc null cells and cells expressing Myc were used to map the topology of Bax in membranes prior to and after mitochondrial permeabilization. Chemical labeling of single cysteine mutants of Bax using a membrane bilayer impermeant cysteine-specific modifying agent revealed that Bax inserted both the 'pore domain' (helices alpha5-alpha6), and the tail-anchor (helix alpha9) into membranes prior to oligomerization and membrane permeabilization. Additional topology changes for Bax were not required in Myc-expressing cells to promote oligomerization and cytochrome c release. Our results suggest that unlike most pore-forming proteins, Bax membrane permeabilization results from oligomerization of transmembrane monomers rather than concerted insertion of the pore domains of a preformed oligomer.
Bax通过一种尚未明确的机制使线粒体外膜通透化，从而促进细胞死亡。然而，在缺乏c-myc基因的细胞中，Bax引起的膜通透化被线粒体的变化所阻断，这些变化阻止了Bax的寡聚化。使用药物处理的c-myc缺失细胞和表达Myc的细胞来绘制线粒体通透化前后Bax在膜中的拓扑结构。使用一种膜双层非渗透性半胱氨酸特异性修饰剂对Bax的单个半胱氨酸突变体进行化学标记，结果显示，在寡聚化和膜通透化之前，Bax将“孔结构域”（α5-α6螺旋）和尾锚（α9螺旋）都插入到膜中。在表达Myc的细胞中，促进寡聚化和细胞色素c释放不需要Bax有额外的拓扑结构变化。我们的结果表明，与大多数成孔蛋白不同，Bax的膜通透化是由跨膜单体的寡聚化导致的，而不是由预先形成的寡聚体的孔结构域协同插入导致的。
