Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139.
Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139.
Protein Sci. 2019 Apr;28(4):756-765. doi: 10.1002/pro.3590. Epub 2019 Mar 4.
IGF-motif loops project from the hexameric ring of ClpX and are required for docking with the self-compartmentalized ClpP peptidase, which consists of heptameric rings stacked back-to-back. Here, we show that ATP or ATPγS support assembly by changing the conformation of the ClpX ring, bringing the IGF loops closer to each other and allowing efficient multivalent contacts with docking clefts on ClpP. In single-chain ClpX pseudohexamers, deletion of one or two IGF loops modestly slows association with ClpP but strongly accelerates dissociation of ClpXP complexes. We probe how changes in the sequence and length of the IGF loops affect ClpX-ClpP interactions and show that deletion of one or two IGF loops slows ATP-dependent proteolysis by ClpXP. We also find that ClpXP degradation is less processive when two IGF loops are deleted.
IGF 基序环从 ClpX 的六聚体环中突出，并需要与自我包含的 ClpP 肽酶对接，ClpP 由背对背堆叠的七聚体环组成。在这里，我们表明 ATP 或 ATPγS 通过改变 ClpX 环的构象来支持组装，使 IGF 环彼此靠近，并允许与 ClpP 上的对接裂缝进行有效的多价接触。在单链 ClpX 假六聚体中，缺失一个或两个 IGF 环会适度减缓与 ClpP 的结合，但会强烈加速 ClpXP 复合物的解离。我们探究了 IGF 环的序列和长度变化如何影响 ClpX-ClpP 相互作用，并表明缺失一个或两个 IGF 环会减缓 ClpXP 依赖 ATP 的蛋白水解。我们还发现，当缺失两个 IGF 环时，ClpXP 降解的连续性降低。
