Two distinct mechanisms drive protein translocation across the mitochondrial outer membrane in the late step of the cytochrome b2 import pathway
Two distinct mechanisms drive protein translocation across the mitochondrial outer membrane in the late step of the cytochrome b2 import pathway
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DOI：
10.1073/pnas.96.21.11770
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发表时间：
1999-10-12
影响因子：
11.1
通讯作者：
Endo, T
中科院分区：
文献类型：
--
作者：
Esaki, M;Kanamori, T;Endo, T
细胞色素B（2）进入线粒体由两个步骤组成，前序列的第一部分穿过内膜的移位与紧密折叠的血红素结合结构域穿过外膜的移位相耦合，并且需要膜电位Δ Psi和基质中的线粒体HSP 70（mHSP 70）的功能。一旦血红素结合结构域穿过外膜，多肽链的其余部分穿过外膜的移位变得不依赖于Δ Psi和mHsp 70。在此，我们分析了细胞色素bz融合蛋白转运到膜间空间（IMS）中的晚期Delta Psi-和mHsp 70-独立步骤。含有由间隔片段连接的两个蛋白结构域的细胞色素B（2）融合蛋白进入线粒体的过程在一个阶段被阻止，在该阶段，一个结构域在外膜的每一侧折叠，沿着与停止转移模型一致的途径。成熟大小的易位中间体可以在两个方向上穿过外膜，IMS中蛋白质结构域的稳定促进了正向易位。另一方面，中间大小形式的易位中间体，它保留锚定到内膜，被转运到IMS中的IMS中的蛋白质结构域的稳定性无关。这些结果表明，两种不同的机制，布朗棘轮和锚扩散机制，可以操作的成熟大小的形式和中间大小的形式，分别为细胞色素bz物种的跨膜运动。
The import of cytochrome b(2) into mitochondria consists of two steps, The translocation of the first part of the presequence across the inner membrane is coupled with the translocation of the tightly folded heme-binding domain across the outer membrane and requires a membrane potential Delta Psi and the functions of mitochondrial Hsp70 (mHsp70) in the matrix, Once the heme-binding domain has passed the outer membrane, the translocation of the rest of the polypeptide chain across the outer membrane becomes independent of Delta Psi and mHsp70. Here we analyzed the late Delta Psi- and mHsp70-independent step in the transport of cytochrome bz fusion proteins into the intermembrane space (IMS), The import of the cytochrome b(2) fusion proteins containing two protein domains linked by a spacer segment into mitochondria was arrested at a stage at which one domain folded on each side of the outer membrane, along the pathway that is consistent with the stop-transfer model. The mature-size form of the translocation intermediate could move across the outer membrane in both directions, and the stabilization of the protein domain in the IMS promoted the forward translocation. On the other hand, the intermediate-size form of the translocation intermediate, which retains the anchorage to the inner membrane, was transported into the IMS independently of the stability of the protein domain in the IMS. These results suggest that two distinct mechanisms, the Brownian ratchet and the anchor diffusion mechanisms, can operate for the transmembrane movement of the mature-size form and the intermediate-size form, respectively, of cytochrome bz species.