Tim23p contains separate and distinct signals for targeting to mitochondria and insertion into the inner membrane
Tim23p contains separate and distinct signals for targeting to mitochondria and insertion into the inner membrane
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DOI：
10.1091/mbc.9.9.2577
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发表时间：
1998-09-01
影响因子：
3.3
通讯作者：
Jensen, RE
中科院分区：
文献类型：
--
作者：
Davis, AJ;Ryan, KR;Jensen, RE
Tim23蛋白是酵母线粒体蛋白输入途径中重要的内膜成分。Tim23p不携带氨基末端序列；因此，靶向信息存在于成熟蛋白中。Tim23p通过四个跨膜片段锚定在IM中，并具有两个面向基质的正电荷环。为了确定Tim23p的输入信号，我们构建了几个Tim23蛋白的改变版本，并研究了它们在酵母细胞中的功能和输入，以及它们在分离线粒体中的输入。我们用丙氨酸残基替换了一个或两个环中的带正电荷的氨基酸，发现进入线粒体不需要正电荷，但至少需要一个带正电荷的环才能插入IM。此外，我们发现将Tim23p靶向线粒体的信号至少在两个疏水跨膜片段中携带。我们的研究结果表明，Tim23p包含单独的输入信号：将Tim23p靶向到线粒体的疏水片段，以及插入到IM的带正电环。因此，我们认为Tim23p至少通过两个不同的步骤被导入线粒体。
The Tim23 protein is an essential inner membrane (IM) component of the yeast mitochondrial protein import pathway. Tim23p does not carry an amino-terminal presequence; therefore, the targeting information resides within the mature protein. Tim23p is anchored in the IM via four transmembrane segments and has two positively charged loops facing the matrix. To identify the import signal for Tim23p, we have constructed several altered versions of the Tim23 protein and examined their function and import in yeast cells, as well as their import into isolated mitochondria. We replaced the positively charged amino acids in one or both loops with alanine residues and found that the positive charges are not required for import into mitochondria, but at least one positively charged loop is required for insertion into the IM. Furthermore, we find that the signal to target Tim23p to mitochondria is carried in at least two of the hydrophobic transmembrane segments. Our results suggest that Tim23p contains separate import signals: hydrophobic segments for targeting Tim23p to mitochondria, and positively charged loops for insertion into the IM. We therefore propose that Tim23p is imported into mitochondria in at least two distinct steps.