Structures and functions of protein translocator systems

维持线粒体功能完整性的中心过程是将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、膜间隙和基质，因此来自胞质溶胶的线粒体蛋白质的通量应该分支为四个不同的子通量，分别针对四个区室中的每一个。在本研究中，我们的目的是阐明机制的监督和控制的线粒体蛋白质通量在酵母细胞。我们鉴定了5个新的线粒体蛋白质转运子元件，Tom 38，Tom 13，Tim 40，Tim 15和Tim 41。此外，我们还对Tim 15的NMR结构进行了测定，发现Tim 15维持线粒体Hsp 70溶解性的能力是其在酵母细胞生长中的重要功能之一，线粒体蛋白必须展开才能通过转运蛋白通道。在这里，我们发现易位蛋白（Tom 40）本身的易位通道具有分子伴侣样活性，从而促进底物蛋白的解折叠，从而进入狭窄的易位蛋白通道。我们还分析了肌肉蛋白肌联蛋白的免疫球蛋白样模块中的各种稳定/不稳定突变对其从N-末端或C-末端进入线粒体的影响。从N-末端的肌联蛋白模块的进口上的突变的影响相关以及与那些在原子力显微镜（AFM）测量中的强制机械展开。另一方面，进口的肌联蛋白模块从N-末端是敏感的N-末端区域的突变，但不是那些在C-末端区域，在AFM实验中影响抵抗全球展开。我们提出线粒体输入系统可以通过降低解折叠中间体的稳定性来催化前体解折叠。

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.