PROTEASOME (26S PROTEASOME)

这个子项目是许多研究子项目中利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 蛋白酶体是存在于所有真核生物和古生物以及一些细菌中的大型动态蛋白质复合体。蛋白酶体的主要功能是通过以一种依赖于ATP的方式断裂多肽键来降解错误折叠或受损的蛋白质。聚合的泛素链作为一个降解信号，将目标蛋白携带到蛋白酶体，在那里底物被蛋白分解。蛋白酶体是细胞调节特定蛋白质浓度和降解错误折叠蛋白质的主要机制的一部分。降解过程产生大约七到八个氨基酸长的多肽，然后可以进一步降解成氨基酸，用于合成新的蛋白质。泛素-蛋白酶体降解途径在许多细胞过程中都是必不可少的，包括细胞周期调节、DNA修复、细胞凋亡、信号转导和蛋白质质量控制。 我们将用单颗粒低温电子显微镜研究牛26S蛋白酶体的结构。这项建议的具体目的是：1)在亚纳米分辨率下解决和比较单帽26S和双帽30S蛋白酶体的结构；2)用低温EM比较无帽20S的溶液结构和20S的X射线结构；3)通过比较26S和30S的低温EM结构和20S的已知结构(S)，进一步阐明26S蛋白酶体的门打开机制，其中环(S)的门保持关闭，以阻止甚至展开的底物的自由进入。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Proteasomes are large dynamic protein complexes existing inside all eukaryotes and archaea, as well as in some bacteria. The major function of the proteasome is to degrade misfolded or damaged proteins by breaking peptide bonds in an ATP-dependent manner. The polymerized ubiquitin chain acts as a degradation signal that carries the target proteins to the proteasome, where the substrate is proteolytically broken down. Proteasomes are part of a major mechanism by which cells regulate the concentration of particular proteins and degrade misfolded proteins. The degradation process yields peptides of about seven to eight amino acids long, which can then be further degraded into amino acids and used in synthesizing new proteins. The ubiquitin-proteasome degradation pathway is essential for many cellular processes, including cell-cycle regulation, DNA repair, apoptosis, signal transduction, and protein quality control. We are going to examine the structures of Bovine 26S proteasomes by single-particle cryo-EM. The specific aims for this proposal are: 1) to solve and compare the structures of single-capped 26S proteasome and double-capped 30S proteasome at subnanometer resolution; 2) to compare the solution structure of non-capped 20S by cryo-EM with the X-ray structure of 20S; 3) to further elucidate the gate opening mechanism of the 26S proteasome by comparing the cryo-EM structures of 26S and 30S with the known structure(s) of 20S, in which the gate in ¿¿ ring(s) remains closed to block the free entry of even unfolded substrates.