The relationship between a molecular chaperone and protease : The discovery of NDP kinase like activity of a chaperone, and degeneration diseases.

泛素-蛋白酶体系统中的伴侣功能&细胞蛋白水解酶和分子伴侣在细胞内蛋白质分解代谢中起着重要作用。泛素-蛋白酶体系统(UPS)是选择性降解蛋白质的质量控制机制的核心组成部分。其中，分子伴侣通过重塑蛋白质底物的构象来激活蛋白酶体的降解。在此之前，我们发现20S蛋白酶体除了具有蛋白水解性外，还具有ATP/ADP交换活性。在这里，我们表明，20S蛋白酶体保护了几个热变性蛋白质的不可逆聚集，导致底物保持在未折叠状态，以便随后降解。此外，我们发现VCP在UPS的功能调节中起着重要作用，它在蛋白酶体底物被降解之前与其相互作用。Hsp7O的ATP/ADP交换活性及其反应机理我们以前报道过，在生理浓度的ATP和ADP存在的情况下，Hsp7O催化了ATP/ADP交换反应。在本研究中，我们通过定点突变鉴定了第二个金属结合基序和Hsp70ATPase结构域与结合的ATP(蛋白质数据库编码为Hsp70 ATPase结构域，1HJO)的晶体结构，发现第二个金属结合位点包括一个由His227、Glu231和Asp232配位的环，与第一个金属结合位点合作参与了ATP/ADP交换反应。另一方面，与Hsp70结合的ADP显著抑制Hsp70的伴侣功能。这些结果可能为更好地理解Hsp70重复底物结合/释放的ATP/ADP交换反应提供重要线索。

<The chaperone functions in the ubiquitin-proteasome system>Cellular proteases and molecular chaperones play important roles in the intracellular protein catabolism. The ubiqitin-proteasome system (UPS) is a central component of the quality control mechanism that selectively degrades proteins. Among this pathway, it has been assumed that molecular chaperones activate proteasomal degradation by remodeling the conformation of protein substrate. Previously, we found that the 20S proteasome exhibits an ATP/ADP exchange activity other than proteolytic activities. Here we show that the 20S proteasome protects several heat-denatured proteins as to irreversible aggregation, leading to a maintenance of substrates in an unfolded state for subsequent degradation. Further, we found that VCP plays an important role in mediating the function of the UPS, by interacting with proteasome substrates before they are degraded. <The ATP/ADP exchange activity of Hsp7O and its reaction mechanism>We have previously reported that, in the presence of physiological concentrations of ATP and ADP, Hsp7O catalyses an ATP/ADP exchange reaction. In this study, we characterized the second metal-binding motif by site-directed mutagenesis and the crystal structure of the Hsp7O ATPase domain with bound ATP (Protein Data Bank code for Hsp70 ATPase domain, 1hjo), and found that the second metal-binding site, comprising a loop co-ordinated by His227, Glu231 and Asp232, participates in an ATP/ADP exchange reaction, in co-operation with the first metal-biding site. On the other hand, ADP bound to Hsp70 significantly inhibited the chaperone functionof Hsp70. These results may give an important clue for a better understanding of the ATP/ADP exchange reaction for repeated cycles of substrate binding/release by Hsp70.