The mechanistic target of rapamycin complex 1 (mTORC1) plays a central role in integrating environmental cues to regulate cellular processes including growth, metabolism, and autophagy. It phosphorylates canonical substrates such as S6K and 4EBP1 in response to amino acids and growth factors, as well as non-canonical substrates like TFEB in response to amino acids alone. Our previous cryo-EM work showed that TFEB recruitment by mTORC1 requires an additional Rag-Ragulator complex, strictly dependent on RagC-GDP. Building on this, we have now combined a reconstituted membrane system with cryo-EM to uncover that mTORC1 activation for 4EBP1 phosphorylation depends on synergistic interactions among Rheb, Rag-Ragulator, and membrane engagement, mediated by specific residues in mTOR and Raptor. Structural analysis further revealed distinct conformations of the mTOR-Rheb-mLST8 subcomplex and additional Rag-Ragulator binding sites, offering new insights into the molecular architecture and activation mechanism of mTORC1 on membranes for canonical substrates.
Cui et al. (Sun,) studied this question.