Abstract IA10: Structure and dynamics of Rag heterodimers in a complex with mTORC1

Eukaryotic cells coordinate growth with the availability of nutrients through the protein kinase complex mTORC1, which is part of a pathway that is often upregulated in cancer. The mTORC1 complex is activated by association with two types of GTPases, Rags and RHEB. The heterodimeric Rag GTPases are key components in the activation of the mTORC1 pathway in response to amino acids. The Rag heterodimer interacts with the RAPTOR subunit of mTORC1 in a manner dependent on the nucleotide-bound states of its constituent GTPases. We used hydrogen/deuterium exchange mass spectrometry (HDX-MS) to map the interface of RAPTOR with an active Rag heterodimer, and we determined X-ray crystal structures of human Rag heterodimers in several nucleotide-bound states. Our high-resolution crystal structure of an oncogenic mutant heterodimer enabled us to interpret the cryo-EM structure of a complex of mTORC1 with the mutant RagA/C heterodimer. The cryo-EM structure shows that the G-domains from both Rags contact helical repeats of the RAPTOR subunit of mTORC1, but the GTP-bound RagA G domain forms almost all of the interface. The structure suggests how the nucleotide state of RagA is coordinated with the nucleotide state of RagC. The conformation of mTORC1 in a complex with the Rags is nearly identical to the apo mTORC1 complex, suggesting that the primary role of Rag binding is to recruit the mTORC1 complex to the lysosomal surface in the presence of the Ragulator complex. Citation Format: Madhan Anandapadamanaban, Olga Perisic, Alex Berndt, Glenn R Masson, Jonathan Kaufman, Stephen H. McLaughlin, Chris M. Johnson, David M. Sabatini, Roger L. Williams. Structure and dynamics of Rag heterodimers in a complex with mTORC1 [abstract]. In: Proceedings of the AACR Special Conference on Targeting PI3K/mTOR Signaling; 2018 Nov 30-Dec 8; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(10_Suppl):Abstract nr IA10.