Chen-Levy Z, Cleary M L
Department of Pathology, Stanford University School of Medicine, California 94305.
J Biol Chem. 1990 Mar 25;265(9):4929-33.
The Bcl-2 oncogenic protein was synthesized in vitro and shown to post-translationally integrate asymmetrically into microsomal membranes with no requirement for an amino-terminal signal sequence. Instead, a carboxyl-terminal hydrophobic domain of Bcl-2 served as an insertion sequence essential for membrane assembly since a Bcl-2 mutant lacking this domain completely lost its ability to associate with microsomal membranes. The data demonstrate that Bcl-2 is tightly associated with the lipid bilayer with the nature of an integral membrane protein. The membrane orientation of Bcl-2 was determined using a protease protection assay, which showed that it is predominantly localized to the cytoplasmic face of membranes. A similar type of membrane processing has been shown for cytochrome b5 and also suggested for the viral oncogenic protein polyoma middle-T antigen.
Bcl-2致癌蛋白在体外合成，并显示其在翻译后不对称地整合到微粒体膜中，且不需要氨基末端信号序列。相反，Bcl-2的羧基末端疏水结构域作为膜组装所必需的插入序列，因为缺乏该结构域的Bcl-2突变体完全丧失了与微粒体膜结合的能力。数据表明，Bcl-2以整合膜蛋白的性质与脂质双层紧密结合。使用蛋白酶保护试验确定了Bcl-2的膜取向，结果表明它主要定位于膜的细胞质面。细胞色素b5也显示出类似类型的膜加工过程，病毒致癌蛋白多瘤中T抗原也有类似的情况。
