| Co-Investigator(Kenkyū-buntansha) |
TANAKA Keiji Department Enzyme Pathology, The University of Tokushima, Assistant Professor, 酵素科学研究センター, 助手 (10108871)
YOSHIMURA Tetsuro Department of Enzyme Regulation, The University of Tokushima, Associate Professo, 酵素科学研究センター, 助教授 (30035472)
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| Research Abstract |
(1) Structural Analysis of Proteasomes at the Molecular Level : We demonstrated that proteasomes are found as two isoforms in cells. One is the ATP-independent 20S form and the other is an ATP-dependent 26S form. Various physical analyzes showed that molecular masses of these two forms are determined to be approximately 750 kDa and 2000 kDa, respectively. The primary structures of 7 alpha-type and 9 beta-type subunits of the 20S proteasome complex in human, rat and yeast were determined by their cDNA cloning. Based on the homology analysis, we proposed the novel term "the proteasome gene family" for these highly homologous gene groups. Furthermore, we have prepared the large crystals of the bovine 20S proteasome and carried out its preliminary X-ray analysis. By electron microscopy, we proposed the "caterpillar-shape" model for the 26S proteasome, consisting of approximately 50 non-identical subunits. The 26S proteasome was found to be the unusually large supra-molecular complex.
(2) Molecular Functions of Proteasomes : The 26S proteasome was demonstrated to be an ATP-dependent protease catalyzing selective degradation of target proteins conjugated with multiple ubiquitins as the degradation signal. Moreover, we found for the first time that ornithine decarboxylase, a most short-lived enzyme in cells responsible for biosynthesis of polyamines, was degraded ATP-dependently by the 26S proteasome without ubiquitination.
(3) Physiological Functions of Proteasomes : The 26S proteasome degraded various nuclear oncoproteins, such as Mos, Fos and Myc, closely related with cell cycle progression in an ATP-, ubiquitin-dependent fashion, suggesting possible involvement of the proteasome in cell cycle regulation. In addition, we found that gamma-interferon induced proteasomes with different subunit organizations for acquirement of the functional diversity and suggested that proteasoms play an essential role for the MHC class-I restricted antigen processing pathway.
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