在酸性pH值下Bcl-2的胞浆结构域通过低聚反应在脂质体膜上成孔

The Cytosolic Domain of Bcl-2 Oligomerizes to Form Pores in Model Mitochondrial Outer Membrane at Acidic pH

促凋亡蛋白Bax和抗凋亡蛋白Bcl-2的三维结构与白喉毒素和大肠杆菌成孔结构域极其相似。与结构相似性一致的是,现有的研究表明Bax和Bcl-2均具有成孔特性。但具有成孔特性的多种蛋白,其成孔的机制却不尽相同。Bax和白喉毒素是通过形成寡聚体成孔,而大肠菌素A却通过形成单体成孔。虽然现有的研究发现Bcl-2可以在正常细胞和凋亡细胞的线粒体形成寡聚体,但对低聚反应是否参与成孔却知道甚少。为了探讨Bcl-2的成孔机制,本文利用Bcl-2的纯化蛋白和脂质体膜研究了其成孔过程。结果发现:Bcl-2的孔径大小与其浓度有关;在一定的浓度下,脂质体包埋的小分子物质比大分子物质可以更快地从脂质体释放;预形成的Bcl-2寡聚体引起的从脂质体的物质释放明显快于Bcl-2单体。因此,研究结果提示:Bcl-2的成孔与其低聚反应有关。

The three dimensional structures of both pro-apoptotic Bax and anti-apoptotic Bcl-2 are strikingly similar to that of pore-forming domains of diphtheria toxin and E. coli colicins. Consistent with the structural similarity, both Bax and Bcl-2 have been shown to possess pore-forming property in the membrane. However, these pore-forming proteins form pores via different mechanisms. While Bax and diphtheria toxin form pores via oligomerization, the colicin pore is formed only by colicin monomers. Although the oligomers of Bcl-2 proteins have been found in the mitochondria of both healthy and apoptotic cells, it is unknown whether or not oligomerization is involved in the pore formation. To determine the mechanism of Bel-2 pore formation, we reconstituted the pore-forming process of Bcl-2 using purified proteins and liposomes. We found that Bel-2 pore size depended on Bcl-2 concentration, and the release of smaller entrapped molecules was faster than that of larger ones from liposomes at a given Bcl-2 concentration. Moreover, the rate of dye release mediated by pre-formed wild-type Bcl-2 oligomers or by the mutant Bcl-Z monomers with a higher homo-association affinity was much higher than that by wild-type Bcl-2 monomers. Together, it is suggested that oligomerization is likely involved in Bcl-2 pore formation.