Structural basis for growth factor and nutrient signal integration on the lysosomal membrane by mTORC1.

Mechanistic target of rapamycin complex 1 (mTORC1), which consists of mTOR, Raptor, and mLST8, receives signaling inputs from growth factor signals and nutrients. These signals are mediated by the Rheb and Rag small GTPases, respectively, which activate mTORC1 on the cytosolic face of the lysosome membrane. We biochemically reconstituted the activation of mTORC1 on membranes by physiological submicromolar concentrations of Rheb, Rags, and Ragulator. We determined the cryo-EM structure and found that Raptor and mTOR directly interact with the membrane at anchor points separated by up to 230 Å across the membrane surface. Full engagement of the membrane anchors is required for maximal activation, which is brought about by alignment of the catalytic residues in the mTOR kinase active site. The observations show at the molecular and atomic scale how converging signals from growth factors and nutrients drive mTORC1 recruitment to and activation on the lysosomal membrane in a three-step process, consisting of (1) Rag-Ragulator-driven recruitment to within ~100 Å of the lysosomal membrane, (2) Rheb-driven recruitment to within ~40 Å, and finally (3) direct engagement of mTOR and Raptor with the membrane. The combination of Rheb and membrane engagement leads to full catalytic activation, providing a structural explanation for growth factor and nutrient signal integration at the lysosome.