Bischoff Lukas, Berninghausen Otto, Beckmann Roland
Gene Center and Center for integrated Protein Science Munich, Department of Biochemistry, Feodor-Lynen-Strasse 25, University of Munich, 81377 Munich, Germany.
Gene Center and Center for integrated Protein Science Munich, Department of Biochemistry, Feodor-Lynen-Strasse 25, University of Munich, 81377 Munich, Germany.
Cell Rep. 2014 Oct 23;9(2):469-75. doi: 10.1016/j.celrep.2014.09.011. Epub 2014 Oct 9.
Elevated levels of the free amino acid L-tryptophan (L-Trp) trigger expression of the tryptophanase tnaCAB operon in E. coli. Activation depends on tryptophan-dependent ribosomal stalling during translation of the upstream TnaC peptide. Here, we present a cryoelectron microscopy (cryo-EM) reconstruction at 3.8 Å resolution of a ribosome stalled by the TnaC peptide. Unexpectedly, we observe two L-Trp molecules in the ribosomal exit tunnel coordinated within composite hydrophobic pockets formed by the nascent TnaC peptide and the tunnel wall. As a result, the peptidyl transferase center (PTC) adopts a distinct conformation that precludes productive accommodation of release factor 2 (RF2), thereby inducing translational stalling. Collectively, our results demonstrate how the translating ribosome can act as a small molecule sensor for gene regulation.
游离氨基酸L-色氨酸（L-Trp）水平升高会触发大肠杆菌中色氨酸酶tnaCAB操纵子的表达。激活取决于上游TnaC肽翻译过程中色氨酸依赖性核糖体停滞。在此，我们展示了一个由TnaC肽停滞的核糖体在3.8埃分辨率下的冷冻电子显微镜（cryo-EM）重建。出乎意料的是，我们在核糖体出口通道中观察到两个L-Trp分子，它们在由新生TnaC肽和通道壁形成的复合疏水口袋内协调排列。结果，肽基转移酶中心（PTC）采用了一种独特的构象，这种构象排除了释放因子2（RF2）的有效容纳，从而诱导翻译停滞。总体而言，我们的结果证明了正在翻译的核糖体如何作为基因调控的小分子传感器。
