Institute of Molecular Biology and Biophysics, ETH, Zurich, Switzerland.
Laboratory of Biomolecular Research, Division of Biology and Chemistry, Paul Scherrer Institute, Villigen, Switzerland.
Nat Commun. 2022 Feb 24;13(1):1045. doi: 10.1038/s41467-022-28685-y.
Adenylyl cyclase 9 (AC9) is a membrane-bound enzyme that converts ATP into cAMP. The enzyme is weakly activated by forskolin, fully activated by the G protein Gαs subunit and is autoinhibited by the AC9 C-terminus. Although our recent structural studies of the AC9-Gαs complex provided the framework for understanding AC9 autoinhibition, the conformational changes that AC9 undergoes in response to activator binding remains poorly understood. Here, we present the cryo-EM structures of AC9 in several distinct states: (i) AC9 bound to a nucleotide inhibitor MANT-GTP, (ii) bound to an artificial activator (DARPin C4) and MANT-GTP, (iii) bound to DARPin C4 and a nucleotide analogue ATPαS, (iv) bound to Gαs and MANT-GTP. The artificial activator DARPin C4 partially activates AC9 by binding at a site that overlaps with the Gαs binding site. Together with the previously observed occluded and forskolin-bound conformations, structural comparisons of AC9 in the four conformations described here show that secondary structure rearrangements in the region surrounding the forskolin binding site are essential for AC9 activation.
腺苷酸环化酶 9（AC9）是一种膜结合酶，可将 ATP 转化为 cAMP。该酶被 forskolin 弱激活，被 G 蛋白 Gαs 亚基完全激活，并被 AC9 C 端自身抑制。尽管我们最近对 AC9-Gαs 复合物的结构研究为理解 AC9 自身抑制提供了框架，但 AC9 对激活剂结合的构象变化仍知之甚少。在这里，我们展示了 AC9 在几种不同状态下的低温电子显微镜结构：（i）与核苷酸抑制剂 MANT-GTP 结合的 AC9，（ii）与人工激活剂（DARPin C4）和 MANT-GTP 结合的 AC9，（iii）与 DARPin C4 和核苷酸类似物 ATPαS 结合的 AC9，（iv）与 Gαs 和 MANT-GTP 结合的 AC9。人工激活剂 DARPin C4 通过与 Gαs 结合位点重叠的位点结合，部分激活 AC9。与之前观察到的封闭和 forskolin 结合构象一起，对这里描述的 AC9 的四种构象进行的结构比较表明，围绕 forskolin 结合位点的二级结构重排对于 AC9 的激活至关重要。
