Pohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang, Kyungbuk 790-784, Korea.
J Biol Chem. 2012 Aug 24;287(35):29648-53. doi: 10.1074/jbc.C112.384420. Epub 2012 Jul 17.
The heterodimeric Rag GTPases consisting of RagA (or RagB) and RagC (or RagD) are the key regulator activating the target of rapamycin complex 1 (TORC1) in response to the level of amino acids. The heterodimer between GTP-loaded RagA/B and GDP-loaded RagC/D is the most active form that binds Raptor and leads to the activation of TORC1. Here, we present the crystal structure of Gtr1p(GTP)-Gtr2p(GDP), the active yeast Rag GTPase heterodimer. The structure reveals that GTP-to-GDP conversion on Gtr2p results in a large conformational transition of this subunit, including a large scale rearrangement of a long segment whose corresponding region in RagA is involved in binding to Raptor. In addition, the two GTPase domains of the heterodimer are brought to contact with each other, but without causing any conformational change of the Gtr1p subunit. These features explain how the nucleotide-bound statuses of the two GTPases subunits switch the Raptor binding affinity on and off.
由 RagA（或 RagB）和 RagC（或 RagD）组成的异二聚 Rag GTPases 是响应氨基酸水平激活雷帕霉素靶蛋白复合物 1（TORC1）的关键调节剂。与 GDP 结合的 RagC/D 负载的 GTP-RagA/B 异二聚体是最活跃的形式，它与 Raptor 结合并导致 TORC1 的激活。在这里，我们展示了 Gtr1p(GTP)-Gtr2p(GDP)，即活性酵母 Rag GTPase 异二聚体的晶体结构。该结构表明，Gtr2p 上的 GTP 到 GDP 的转换导致该亚基发生大的构象转变，包括长片段的大规模重排，该片段在 RagA 中涉及与 Raptor 的结合。此外，异二聚体的两个 GTPase 结构域相互接触，但不会引起 Gtr1p 亚基的任何构象变化。这些特征解释了两个 GTPase 亚基的核苷酸结合状态如何开启和关闭 Raptor 结合亲和力。
