Doonan S, Marra E, Passarella S, Saccone C, Quagliariello E
Int Rev Cytol. 1984;91:141-86. doi: 10.1016/s0074-7696(08)61316-9.
There is still much that is obscure concerning the transport of proteins into or through the mitochondrial membrane systems. In addition, as pointed out previously, it is unlikely that the details of the process are the same for proteins destined for different compartments of the organelle. A brief summary of the process for matrix proteins might be as follows: The proteins are synthesized on free polysomes as precursors of higher molecular weight than the native forms. These precursors are liberated into the cell cytosol and subsequently translocated into the mitochondria. This timing might be different in yeast under some circumstances, synthesis being completed in association with the mitochondria. The precursors interact with a receptor in the outer mitochondrial membrane interaction being mediated by the presequences of the precursors. The presequences therefore act as addressing signals as well as possibly playing a role in one or all of (a) solubilization of precursors, (b) prevention of premature assembly into multimeric structures, or (c) maintenance of nonnative configurations required for transport. Interaction occurs with a second receptor, this time in the inner membrane of the mitochondria, interaction being with multiple sites in the polypeptide chain. Transport across the inner membrane then occurs, this transport depending on a transmembrane electrochemical gradient of which the proton component is the essential part. Transport is accompanied or followed by proteolysis of the prepiece, and formation of the native structure. While steps 1 and 2 of this sequence can be considered well established, the remaining steps are still poorly understood or purely hypothetical. Nevertheless, this sequence of events is consistent with known facts about the process and provides a framework for future investigations.
关于蛋白质进入线粒体膜系统或穿过该系统的过程，仍有许多不明之处。此外，如前所述，对于运往该细胞器不同区室的蛋白质，该过程的细节不太可能相同。线粒体基质蛋白的过程简要总结如下：蛋白质在游离多聚核糖体上作为比天然形式分子量更高的前体进行合成。这些前体被释放到细胞质中，随后转运到线粒体中。在某些情况下，酵母中的这个时间安排可能不同，合成会在线粒体的参与下完成。前体与线粒体外膜上的受体相互作用，这种相互作用由前体的前导序列介导。因此，前导序列既作为寻址信号，也可能在以下一个或所有方面发挥作用：(a) 前体的溶解，(b) 防止过早组装成多聚体结构，或 (c) 维持转运所需的非天然构象。接着与第二个受体相互作用，这次是在线粒体内膜上，与多肽链中的多个位点相互作用。然后发生跨内膜的转运，这种转运取决于跨膜电化学梯度，其中质子成分是关键部分。转运过程伴随着或紧接着前肽的蛋白水解以及天然结构的形成。虽然这个序列的步骤1和2可以被认为是确定的，但其余步骤仍知之甚少或纯粹是假设的。然而，这一系列事件与关于该过程的已知事实相符，并为未来的研究提供了一个框架。
