Janiak F, Leber B, Andrews D W
Department of Biochemistry, McMaster University, Hamilton, Ontario, Canada.
J Biol Chem. 1994 Apr 1;269(13):9842-9.
Bcl-2 is thought to associate spontaneously with membranes via a carboxyl-terminal hydrophobic domain by a mechanism analogous to that of cytochrome b5. We have examined the association of Bcl-2 with a variety of highly purified intracellular membranes in vitro. Fusion proteins were used to assess directly the role of the carboxyl-terminal hydrophobic domain of Bcl-2 in membrane association. Although this domain of Bcl-2 was sufficient to promote the association of a normally cytosolic polypeptide with either microsomal or mitochondrial membranes additional nonhydrophobic amino-terminal residues were required for membrane integration. Furthermore, direct comparison of membrane binding of Bcl-2 and cytochrome b5 revealed that similar to cytochrome b5, membrane targeting of Bcl-2 was not dependent on protease-sensitive components of the recipient membranes. In competition experiments, cytochrome b5 demonstrated the expected preference for integration into endoplasmic reticulum membranes. In contrast, the data presented here suggest that Bcl-2 is targeted to the cytoplasmic surface of multiple intracellular membranes, both in vitro and in human leukemic cells.
Bcl-2被认为通过类似于细胞色素b5的机制，经由羧基末端疏水结构域自发地与膜结合。我们已经在体外研究了Bcl-2与多种高度纯化的细胞内膜的结合情况。利用融合蛋白直接评估Bcl-2羧基末端疏水结构域在膜结合中的作用。尽管Bcl-2的这一结构域足以促进正常胞质多肽与微粒体膜或线粒体膜的结合，但膜整合还需要额外的非疏水氨基末端残基。此外，对Bcl-2和细胞色素b5膜结合的直接比较表明，与细胞色素b5类似，Bcl-2的膜靶向不依赖于受体膜中蛋白酶敏感成分。在竞争实验中，细胞色素b5表现出预期的整合到内质网膜中的偏好。相比之下，此处给出的数据表明，无论是在体外还是在人白血病细胞中，Bcl-2都靶向多种细胞内膜的细胞质表面。
