Rosenzweig Rina, Sekhar Ashok, Nagesh Jayashree, Kay Lewis E
Department of Molecular Genetics, The University of Toronto, Toronto, Canada.
Department of Biochemistry, The University of Toronto, Toronto, Canada.
Elife. 2017 Jul 14;6:e28030. doi: 10.7554/eLife.28030.
The Hsp70 chaperone system is integrated into a myriad of biochemical processes that are critical for cellular proteostasis. Although detailed pictures of Hsp70 bound with peptides have emerged, correspondingly detailed structural information on complexes with folding-competent substrates remains lacking. Here we report a methyl-TROSY based solution NMR study showing that the version of Hsp70, DnaK, binds to as many as four distinct sites on a small 53-residue client protein, hTRF1. A fraction of hTRF1 chains are also bound to two DnaK molecules simultaneously, resulting in a mixture of DnaK-substrate sub-ensembles that are structurally heterogeneous. The interactions of Hsp70 with a client protein at different sites results in a fuzzy chaperone-substrate ensemble and suggests a mechanism for Hsp70 function whereby the structural heterogeneity of released substrate molecules enables them to circumvent kinetic traps in their conformational free energy landscape and fold efficiently to the native state.
热休克蛋白70（Hsp70）伴侣系统整合到众多对细胞蛋白质稳态至关重要的生化过程中。尽管已出现Hsp70与肽结合的详细图像，但关于与具有折叠能力的底物形成的复合物的相应详细结构信息仍然缺乏。在此，我们报告一项基于甲基横向弛豫优化谱（methyl-TROSY）的溶液核磁共振（NMR）研究，结果表明Hsp70的DnaK变体可与一个由53个残基组成的小客户蛋白hTRF1上多达四个不同位点结合。一部分hTRF1链还同时与两个DnaK分子结合，导致形成结构异质的DnaK-底物亚集合混合物。Hsp70与客户蛋白在不同位点的相互作用导致形成模糊的伴侣-底物集合，并提示了一种Hsp70功能机制，即释放的底物分子的结构异质性使它们能够避开其构象自由能景观中的动力学陷阱并有效折叠成天然状态。
