Mechanism of Selective Degradation of Proteins

为了分析细胞内蛋白质选择性降解的机制，主要研究了细胞内两种主要的蛋白酶系统，蛋白酶体和钙蛋白酶。Suzuki成功地在2.3Å上分析了calpain的晶体结构，发现calpain是一种无活性的前酶，需要钙诱导大的构象变化才能变得活跃。功能未知的结构域III负责钙诱导的构象变化和生物膜的易位。Maki鉴定了4个由选择性剪接产生的calpastatin新种。Tanaka鉴定出26S蛋白酶体多泛素受体的5种选择性剪接变体，它们在不同组织中表达不同，从而表现出不同的功能。发现了一种具有不同于26S蛋白酶体的催化和调控亚基的内源性抗原加工的新蛋白酶体，并命名为免疫蛋白酶体。进一步，帕金森病的基因产物被鉴定为泛素连接酶，提示泛素连接酶靶蛋白的沉积可能是帕金森病的病因。Yamao发现了一种新的裂变酵母降解含有E2的M期细胞周期蛋白的蛋白水解体系。村上阐明了蛋白酶体结合和降解鸟氨酸脱羧酶的分子机制以及抗酶和ATP在这一过程中的作用。Kido分析了流感病毒感染宿主细胞的分子基础，这种感染需要宿主细胞胰蛋白酶clara特异性降解病毒膜蛋白。此外，还发现了一种特异性的克拉拉胰蛋白酶抑制蛋白。

To analyze mechanisms for selective intracellular protein degradation, two major protease systems in cells, proteasome and calpain, were mainly studied. Suzuki succeeded to analyze the crystal structure of calpain at 2.3Å and found that calpain exists as an inactive proenzyme which requires Ca-induced large conformational changes to become active. Domain III of unknown function is responsible for the Ca-induced conformational changes and translocation to biological membrane. Maki identified 4 novel calpastatin species produced by alternative splicing. Tanaka identified 5 alternative splicing variants of poly-ubiquitin receptor of 26S proteasome differently expressed in various tissues and thus showed distinct functions. A novel proteasome species responsible for endogenous antigen processing containing catalytic and regulatory subunits distinct from 26S proteasome was discovered and named immune proteasome. Further, the gene product for Parkinsonism was identified to be ubiquitin ligase suggesting that the deposition of its target protein of the ligase would be the cause of the disease. Yamao identified a novel proteolytic system of fission yeast for degradation of M phase cyclin containing novel E2. Murakami clarified the molecular mechanism for binding and degradation of ornithine decarboxylase by proteasome and the function of antizyme and ATP in the process. Kido analyzed molecular basis for influenza virus infection to host cells that requires specific degradation of virus membrane proteins by host cell tryptase clara. A specific inhibitor protein for clara tryptase was also fund.