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Structures and functions of protein translocator systems

蛋白质易位系统的结构和功能

基本信息

批准号：
14037225
负责人：
ENDO Toshiya
金额：
$ 95.1万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research on Priority Areas
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2006
项目状态：
已结题

项目摘要

The central process in the maintenance of functional integrity of mitochondria is the transport of 500-1000 different mitochondrial precursor proteins to mitochondria. Since mitochondria consist of four compartments, the outer and inner membranes, intermembrane space, and matrix, the flux of mitochondrial proteins from the cytosol should branch off in four different sub-fluxes that are directed for each of the four compartments. In the present study, we aimed at elucidation of the mechanisms for surveillance and control of the mitochondrial protein fluxes in yeast cells. We identified 5 new components, Tom38, Toml3, Tim4O, Timl5, and Tim4l, of the mitochondrial protein translocators. Besides, we determined the NMR structure of Timl5, and found that the ability of Tim15 to maintain solubility of mitochondrial Hsp70 represents one of the essential functions of Tim15 in yeast cell growth.Mitochondrial proteins have to become unfolded to move through the translocator channels. Here we found that the translocation channel of the translocator (Tom40) itself has a chaperone-like activity, thereby promoting unfolding of the substrate proteins to be threaded into the narrow translocator channel. We also analyzed the effects of various stabilization/destabilization mutations in the immunoglobulin-like module of the muscle protein titin on its import from the N-terminus or C-terminus into mitochondria. The effects of mutations on the import of the titin module from the N-terminus correlate well with those on forced mechanical unfolding in atomic force microscopy (AFM) measurements. On the other hand, import of the titin module from the N-terminus is sensitive to mutations in the N-terminal region, but not the ones in the C-terminal region that affect resistance to global unfolding in AFM experiments. We propose that the mitochondrial import system can catalyze precursor unfolding by reducing the stability of unfolding intermediates.

维持线粒体功能完整性的核心过程是将500-1000种不同的线粒体前体蛋白转运到线粒体。由于线粒体由四个区室组成，即外膜和内膜、膜间空间和基质，因此来自细胞质的线粒体蛋白的通量应该分为四个不同的亚通量，分别针对四个区室中的每个区室。在本研究中，我们旨在阐明酵母细胞线粒体蛋白通量的监测和控制机制。我们鉴定出线粒体蛋白易位子的5个新组分：Tom38、Toml3、tim40、tim15和tim41。此外，我们测定了Tim15的NMR结构，发现Tim15维持线粒体Hsp70溶解度的能力是Tim15在酵母细胞生长中的基本功能之一。线粒体蛋白必须展开才能通过转运体通道。在这里，我们发现转运子（Tom40）的易位通道本身具有类似伴侣的活性，从而促进底物蛋白的展开，使其进入狭窄的转运子通道。我们还分析了肌蛋白titin的免疫球蛋白样模块中各种稳定/不稳定突变对其从n端或c端进入线粒体的影响。在原子力显微镜（AFM）测量中，突变对从n端输入titin模块的影响与对强制机械展开的影响密切相关。另一方面，从n端导入titin模块对n端区域的突变敏感，但对影响AFM实验中对全局展开抗性的c端区域的突变不敏感。我们提出线粒体输入系统可以通过降低展开中间体的稳定性来催化前体展开。