| Co-Investigator(Kenkyū-buntansha) |
YOSHIHISA Tohru Nagoya University, RCMS, Associate Professor, 物質科学国際研究センター, 助教授 (60212312)
NISHIKAWA Shuh-ichi Nagoya University, Grad. Sch. of Science, Ass. Prof., 大学院・理学研究科, 助教授 (10252222)
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| Research Abstract |
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,Tom13,Tim40,Tim15,and Tim41,of the mitochondrial protein translocators. In the course of our efforts to assign roles in mitochondrial protein import to these new components, it has become evident that the pathways of mitochondrial protein transport are much more complex than previously envisaged and the processes of translocation across and assembly into mitochondrial membranes are
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controlled in a highly sophisticated manner by cooperation of the mitochondrial translocator complexes. Besides, it is important for the mitochondrial translocator systems to recognize destination signals of substrate proteins, at the branching points in the mitochondrial protein fluxes, and sort them to correct destination routes. In this connection, we found that the general import receptor, Tom20, in the outer membrane, plays important roles in increasing targeting specificity as well as import efficiency, that Tim50 in the inner membrane functions as a presequence receptor, and that substrate proteins for the TIM22 pathway in the inner membrane possess cryptic targeting signals for the TIM23 pathway. One of the important, but still unresolved questions is what drives the protein flux for mitochondria. Here we found that the translocation channel of the translocator itself has a chaperone-like activity, thereby promoting unfolding of the substrate proteins to be threaded into the narrow translocator channel. Less
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