Rinnerthaler Mark, Jarolim Stefanie, Heeren Gino, Palle Elfriede, Perju Simona, Klinger Harald, Bogengruber Edith, Madeo Frank, Braun Ralf J, Breitenbach-Koller Lore, Breitenbach Michael, Laun Peter
Department of Cell Biology, Division of Genetics, University of Salzburg, Austria.
Biochim Biophys Acta. 2006 May-Jun;1757(5-6):631-8. doi: 10.1016/j.bbabio.2006.05.022. Epub 2006 May 20.
The yeast orthologue of mammalian TCTP is here proposed to be named Mmi1p (microtubule and mitochondria interacting protein). This protein displays about 50% amino acid sequence identity with its most distantly related orthologs in higher organisms and therefore probably belongs to a small class of yeast proteins which have housekeeping but so far incompletely known functions needed for every eukaryotic cell. Previous investigations of the protein in both higher cells and yeast revealed that it is highly expressed during active growth, but transcriptionally down-regulated in several kinds of stress situations including starvation stress. In human cells, TCTP presumably has anti-apoptotic functions as it binds to Bcl-XL in vivo. TCTP of higher cells was also shown to interact with the translational machinery. It has acquired an additional function in the mammalian immune system, as it is identical with the histamine releasing factor. Here, we show that in S. cerevisiae induction of apoptosis by mild oxidative stress, replicative ageing or mutation of cdc48 leads to translocation of Mmi1p from the cytoplasm to the mitochondria. Mmi1p is stably but reversibly attached to the outer surface of the mitochondria and can be removed by digestion with proteinase K. Glutathionylation of Mmi1p, which is also induced by oxidants, is not a prerequisite or signal for translocation as shown by replacing the only cysteine of Mmi1p by serine. Mmi1p probably interacts with yeast microtubules as deletion of the gene confers sensitivity to benomyl. Conversely, the deletion mutant displays resistance to hydrogen peroxide stress and shows a small but significant elongation of the mother cell-specific lifespan. Our results so far indicate that Mmi1p is one of the few proteins establishing a functional link between microtubules and mitochondria which may be needed for correct localization of mitochondria during cell division.
哺乳动物TCTP的酵母同源物在此被提议命名为Mmi1p（微管与线粒体相互作用蛋白）。该蛋白与其在高等生物中关系最远的同源物显示出约50%的氨基酸序列同一性，因此可能属于一小类酵母蛋白，这类蛋白具有维持细胞基本功能的作用，但迄今为止其功能在每个真核细胞中尚不完全清楚。先前对高等细胞和酵母中该蛋白的研究表明，它在活跃生长期间高度表达，但在包括饥饿应激在内的几种应激情况下转录下调。在人类细胞中，TCTP可能具有抗凋亡功能，因为它在体内与Bcl-XL结合。高等细胞的TCTP也被证明与翻译机制相互作用。它在哺乳动物免疫系统中获得了额外功能，因为它与组胺释放因子相同。在此，我们表明在酿酒酵母中，轻度氧化应激、复制性衰老或cdc48突变诱导的凋亡会导致Mmi1p从细胞质转移到线粒体。Mmi1p稳定但可逆地附着在线粒体的外表面，并且可以通过蛋白酶K消化去除。如将Mmi1p唯一的半胱氨酸替换为丝氨酸所示，氧化剂诱导的Mmi1p谷胱甘肽化不是转移的先决条件或信号。Mmi1p可能与酵母微管相互作用，因为该基因的缺失赋予了对苯菌灵的敏感性。相反，缺失突变体对过氧化氢应激具有抗性，并且母细胞特异性寿命略有但显著延长。我们目前的结果表明，Mmi1p是在微管和线粒体之间建立功能联系的少数蛋白质之一，这可能是细胞分裂期间线粒体正确定位所必需的。
