Institute for Biophysical Chemistry, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany.
Institute for Virology, Hannover Medical School, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany.
Structure. 2015 May 5;23(5):851-862. doi: 10.1016/j.str.2015.03.012. Epub 2015 Apr 16.
2'-5'-Oligoadenylate synthetases (OASs) produce the second messenger 2'-5'-oligoadenylate, which activates RNase L to induce an intrinsic antiviral state. We report on the crystal structures of catalytic intermediates of OAS1 including the OAS1·dsRNA complex without substrates, with a donor substrate, and with both donor and acceptor substrates. Combined with kinetic studies of point mutants and the previously published structure of the apo form of OAS1, the new data suggest a sequential mechanism of OAS activation and show the individual roles of each component. They reveal a dsRNA-mediated push-pull effect responsible for large conformational changes in OAS1, the catalytic role of the active site Mg(2+), and the structural basis for the 2'-specificity of product formation. Our data reveal similarities and differences in the activation mechanisms of members of the OAS/cyclic GMP-AMP synthase family of innate immune sensors. In particular, they show how helix 3103-α5 blocks the synthesis of cyclic dinucleotides by OAS1.
2'-5'-寡聚腺苷酸合成酶（OASs）产生第二信使 2'-5'-寡聚腺苷酸，激活 RNase L 诱导内在抗病毒状态。我们报告了 OAS1 的催化中间体的晶体结构，包括无底物、有供体底物和有供体和受体底物的 OAS1·dsRNA 复合物。结合点突变的动力学研究和之前报道的 OAS1 的apo 形式的结构，新数据表明 OAS 的激活是一个顺序机制，并显示了每个组件的单独作用。它们揭示了 dsRNA 介导的推拉效应，负责 OAS1 的大构象变化，活性位点 Mg（2+）的催化作用，以及产物形成的 2'-特异性的结构基础。我们的数据揭示了先天免疫传感器的 OAS/cyclic GMP-AMP 合酶家族成员的激活机制的相似和不同之处。特别是，它们展示了如何通过 OAS1 的螺旋 3103-α5 阻断环二核苷酸的合成。
