UC Berkeley

The mechanistic target of rapamycin complex 1 (mTORC1) regulates cell growth andcatabolism by phosphorylating key substrates in response to nutrient fluctuations. Recruitment of mTORC1 to the lysosomal membrane by the Rag-Ragulator complex is important for activation of its kinase activity and interaction with select substrates. The Rag-Ragulator complex is comprised of two small GTPases, Rag A/B and Rag C/D, and the pentameric scaffold protein complex Ragulator. The Rags GTPases exist predominately in an active (RagAGTP:RagCGDP) or inactive (RagAGDP:RagCGTP) state, with mTORC1 binding to the active state. The Rag GTPase's nucleotide state and activity are modulated by two GAPs, FLCN and GATOR1, transitioning the complex between active and inactive forms. Additional protein complexes (KICSTOR, GATOR2) and nutrient sensors (SLC38A9, Castor1, Sestrin2 and Samtor) regulate the activity of these GAPs in response to nutrient levels ultimately regulating the activity of mTORC1. In this work, structural analysis and in vitro reconstitution were used to elucidate the mechanisms of FLCN and GATOR1 regulation. The network of GATOR1 regulation was dissected to understand how the KICSTOR complex regulates GATOR1 and how nutrient sensors Castor1 and Sestrin2 relay information to the GATOR2 complex.