Bcl-2的胞浆结构域在酸性pH的诱导下可与脂质体的膜相结合并在脂质体膜上形成孔径较小的孔(英文)

The Cytosolic Domain of Bcl-2 Forms Small Pores in Model Mitochondrial Outer Membrane After Acidic pH-induced Membrane Association

线粒体外膜的通透性是通过膜蛋白Bcl-2家族间的相互作用调节的。其中,促凋亡蛋白Bax被BH3-on-ly蛋白激活后,可以增加线粒体外膜的通透性,释放细胞色素C。而抗凋亡蛋白Bcl-2则可以保护线粒体外膜。以往的研究表明:两种蛋白都可以在膜上成孔,而且凋亡蛋白Bax成孔与线粒体外膜的通透性密切相关,但有关抗凋亡蛋白Bcl-2的成孔却少有报道。为此,我们利用含有线粒体脂质的脂质体膜研究了无C-末端跨膜序列的重组抗凋亡蛋白(Bcl-2ΔTM)的成孔特性。我们的研究结果显示:Bcl-2ΔTM只能在酸性pH(<5.0)的条件下成孔;酸性pH可诱导Bcl-2ΔTM与脂质体的结合;与Bax可以在膜上形成大孔以释放分子量最大可达2 000 KDa的大分子不同,Bcl-2ΔTM成孔的孔径明显较小,仅仅能让几个KDa的小分子通过。这些结果表明促凋亡蛋白Bax和抗凋亡蛋白Bcl-2可能通过在线粒体外膜上形成孔径不同的孔来参与凋亡的调节:Bax可以在膜上形成大孔释放细胞色素C以促进凋亡,而Bcl-2则在膜上形成小孔参与维持线粒体外膜的正常通透性。另外,我们还发现Bcl-2ΔTM的孔径大小与其浓度有关,提示Bcl-2的成孔与其低聚反应有关。

The permeability of mitochondrial outer membrane （MOM） is regulated by the proteins of the Bcl-2 family via their interactions at the membrane. While pro-apoptotic Bax protein promotes MOM permeabilization （MOMP） releasing cytochrome e after activation by BH3-only protein, anti-apoptotic Bcl-2 protein protects MOM. However both Bax and Bcl-2 can form pores in model membranes. Unlike Bax pore that has been extensively studied and reported to be directly linked to MOMP, Bcl-2 pore is much less known; thus we investigated the pore-forming property of recombinant Bcl-2 lacking the C-terminal transmembrane sequence （Bcl-2△TM） in liposomal membranes of MOM lipids. We found that： （1） Bcl-2 formed pores at acidic pH that induced the association of Bcl-2 with Iipo- some; （2） Bcl-2 pore size was dependent on Bcl-2 concentration, suggesting that oligomerization is involved in Bcl-2 pore formation; （3） Unlike Bax pore that could release large molecules up to 2 mega-Da, Bcl-2 pore was smaller and could only release the molecules of a few kilo-Da. Therefore, Bcl-2 and Bax may form different size pores in MOM, and while the large pore formed by Bax may release cytochrome e during apoptosis, the small pore formed by Bcl-2 may maintain the normal MOM permeability.