Stabilization of G domain conformations in the tRNA-modifying MnmE-GidA complex observed with double electron electron resonance spectroscopy.

MnmE is a GTP-binding protein conserved between bacteria and eukarya. It is a dimeric three-domain protein where the two G domains have to approach each other for activation of the potassium-stimulated GTPase reaction. Together with GidA, in a heterotetrameric alpha(2)beta(2) complex, it is involved in the modification of the wobble uridine base U34 of the first anticodon position of particular tRNAs. Here we show, using various spin-labeled MnmE mutants and EPR spectroscopy, that GidA binding induces large conformational and dynamic changes in MnmE. It stimulates the GTPase reaction by stabilizing the GTP-bound conformation in a potassium-independent manner. Surprisingly, GidA binding influences not only the GTP- but also the GDP-bound conformation. Thus GidA is a new type of regulator for a G protein activated by dimerization.

用双电子电子共振光谱法观察tRNA修饰的MnmE-GidA复合物中G结构域构象的稳定性。

MnmE是细菌和真核生物之间保守的GTP结合蛋白。它是一种二聚体三结构域蛋白质，其中两个G结构域必须相互靠近以激活钾刺激的GTP酶反应。在异四聚α(2)β(2)复合物中，它与GidA一起参与特定tRNAs第一个反密码子位置的摆动尿苷碱基U34的修饰。在这里，我们使用各种自旋标记的MnmE突变体和电子顺磁共振波谱显示，GidA结合诱导MnmE大的构象和动态变化。它通过以不依赖钾的方式稳定GTP结合构象来刺激GTP酶反应。令人惊讶的是，GidA结合不仅影响GTP，而且影响GDP结合构象。因此GidA是一种新型的由二聚化激活的G蛋白调节剂。