Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
Howard Hughes Medical Institute and Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Annu Rev Physiol. 2018 Feb 10;80:413-429. doi: 10.1146/annurev-physiol-021317-121303.
AAA+ proteolytic machines use energy from ATP hydrolysis to degrade damaged, misfolded, or unneeded proteins. Protein degradation occurs within a barrel-shaped self-compartmentalized peptidase. Before protein substrates can enter this peptidase, they must be unfolded and then translocated through the axial pore of an AAA+ ring hexamer. An unstructured region of the protein substrate is initially engaged in the axial pore, and conformational changes in the ring, powered by ATP hydrolysis, generate a mechanical force that pulls on and denatures the substrate. The same conformational changes in the hexameric ring then mediate mechanical translocation of the unfolded polypeptide into the peptidase chamber. For the bacterial ClpXP and ClpAP AAA+ proteases, the mechanical activities of protein unfolding and translocation have been directly visualized by single-molecule optical trapping. These studies in combination with structural and biochemical experiments illuminate many principles that underlie this universal mechanism of ATP-fueled protein unfolding and subsequent destruction.
AAA+ 蛋白酶体利用 ATP 水解产生的能量来降解受损、错误折叠或不需要的蛋白质。蛋白质降解发生在一个桶形的自我分隔的肽酶中。在蛋白质底物进入这个肽酶之前，它们必须先展开，然后穿过 AAA+ 环六聚体的轴向孔进行转运。蛋白质底物的无结构区域最初与轴向孔结合，然后由 ATP 水解驱动的环的构象变化产生机械力，拉动并使底物变性。六聚体环的相同构象变化随后介导未折叠多肽机械性转运到肽酶腔中。对于细菌 ClpXP 和 ClpAP AAA+ 蛋白酶，通过单分子光学捕获直接观察到蛋白质展开和转运的机械活性。这些研究与结构和生化实验相结合，阐明了该普遍的 ATP 驱动蛋白质展开和随后破坏的机制的许多原理。
