Iosefson Ohad, Nager Andrew R, Baker Tania A, Sauer Robert T
Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
1] Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA. [2] Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
Nat Chem Biol. 2015 Mar;11(3):201-6. doi: 10.1038/nchembio.1732. Epub 2015 Jan 19.
Hexameric ATP-dependent proteases and protein remodeling machines use conserved loops that line the axial pore to apply force to substrates during the mechanical processes of protein unfolding and translocation. Whether loops from multiple subunits act independently or coordinately in these processes is a critical aspect of the mechanism but is currently unknown for any AAA+ machine. By studying covalently linked hexamers of the Escherichia coli ClpX unfoldase bearing different numbers and configurations of wild-type and mutant pore loops, we show that loops function synergistically, and the number of wild-type loops required for efficient degradation is dependent on the stability of the protein substrate. Our results support a mechanism in which a power stroke initiated in one subunit of the ClpX hexamer results in the concurrent movement of all six pore loops, which coordinately grip and apply force to the substrate.
六聚体ATP依赖性蛋白酶和蛋白质重塑机器利用排列在轴向孔道的保守环，在蛋白质解折叠和转运的机械过程中对底物施加力。在这些过程中，多个亚基的环是独立作用还是协同作用，是该机制的一个关键方面，但目前对于任何AAA+机器来说都尚不清楚。通过研究带有不同数量和构型的野生型和突变型孔环的大肠杆菌ClpX解折叠酶的共价连接六聚体，我们发现环协同发挥作用，有效降解所需的野生型环数量取决于蛋白质底物的稳定性。我们的结果支持一种机制，即ClpX六聚体的一个亚基引发的动力冲程导致所有六个孔环同时移动，它们协同抓住底物并对其施加力。
