Bacterial Origin of a Mitochondrial Outer Membrane Protein Translocase NEW PERSPECTIVES FROM COMPARATIVE SINGLE CHANNEL ELECTROPHYSIOLOGY
Bacterial Origin of a Mitochondrial Outer Membrane Protein Translocase NEW PERSPECTIVES FROM COMPARATIVE SINGLE CHANNEL ELECTROPHYSIOLOGY
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DOI：
10.1074/jbc.m112.392118
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发表时间：
2012-09-07
影响因子：
4.8
通讯作者：
Wagner, Richard
中科院分区：
文献类型：
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作者：
Harsman, Anke;Niemann, Moritz;Wagner, Richard
线粒体是细菌的祖先，必须从细胞质中输入大部分蛋白质。这一过程由Tom 40介导，Tom 40是一种在线粒体外膜中形成蛋白质转运孔的必需蛋白。Tom 40在几乎所有的真核生物中都是保守的，但其进化起源尚不清楚，因为到目前为止还没有鉴定出细菌的直系同源物。最近，它表明，寄生原生动物布氏锥虫缺乏一个传统的Tom 40，而是采用古老的易位酶的外线粒体膜（ATOM），一种蛋白质，显示出相似性的真核Tom 40和细菌蛋白易位酶的Omp 85家族。在这里，我们提出的电生理单通道数据显示，原子形成一个亲水性孔的大电导和高开放概率。此外，ATOM通道表现出对阳离子分子通过的偏好，这与它可以易位由带正电荷的N-末端前序列靶向的未折叠蛋白质的想法一致。这进一步得到以下事实的支持：添加前序列肽诱导瞬时孔闭合。这些单通道特性与其他蛋白质易位酶的深入比较表明，ATOM非常类似于细菌型蛋白质出口通道，而不是真核Tom 40。我们的研究结果支持这样的想法，ATOM代表细菌Omp 85样蛋白质出口机器和传统的Tom 40，发现在其他真核生物的线粒体之间的进化中间体。
Mitochondria are of bacterial ancestry and have to import most of their proteins from the cytosol. This process is mediated by Tom40, an essential protein that forms the protein-translocating pore in the outer mitochondrial membrane. Tom40 is conserved in virtually all eukaryotes, but its evolutionary origin is unclear because bacterial orthologues have not been identified so far. Recently, it was shown that the parasitic protozoon Trypanosoma brucei lacks a conventional Tom40 and instead employs the archaic translocase of the outer mitochondrial membrane (ATOM), a protein that shows similarities to both eukaryotic Tom40 and bacterial protein translocases of the Omp85 family. Here we present electrophysiological single channel data showing that ATOM forms a hydrophilic pore of large conductance and high open probability. Moreover, ATOM channels exhibit a preference for the passage of cationic molecules consistent with the idea that it may translocate unfolded proteins targeted by positively charged N-terminal presequences. This is further supported by the fact that the addition of a presequence peptide induces transient pore closure. An in-depth comparison of these single channel properties with those of other protein translocases reveals that ATOM closely resembles bacterial-type protein export channels rather than eukaryotic Tom40. Our results support the idea that ATOM represents an evolutionary intermediate between a bacterial Omp85-like protein export machinery and the conventional Tom40 that is found in mitochondria of other eukaryotes.