Mechanisms of mTORC1 activation by RHEB and inhibition by PRAS40

Nature. 2017 Dec 21;552(7685):368-373. doi: 10.1038/nature25023. Epub 2017 Dec 13.


The mechanistic target of rapamycin complex 1 (mTORC1) controls cell growth and metabolism in response to nutrients, energy levels, and growth factors. It contains the atypical kinase mTOR and the RAPTOR subunit that binds to the Tor signalling sequence (TOS) motif of substrates and regulators. mTORC1 is activated by the small GTPase RHEB (Ras homologue enriched in brain) and inhibited by PRAS40. Here we present the 3.0 ångström cryo-electron microscopy structure of mTORC1 and the 3.4 ångström structure of activated RHEB-mTORC1. RHEB binds to mTOR distally from the kinase active site, yet causes a global conformational change that allosterically realigns active-site residues, accelerating catalysis. Cancer-associated hyperactivating mutations map to structural elements that maintain the inactive state, and we provide biochemical evidence that they mimic RHEB relieving auto-inhibition. We also present crystal structures of RAPTOR-TOS motif complexes that define the determinants of TOS recognition, of an mTOR FKBP12-rapamycin-binding (FRB) domain-substrate complex that establishes a second substrate-recruitment mechanism, and of a truncated mTOR-PRAS40 complex that reveals PRAS40 inhibits both substrate-recruitment sites. These findings help explain how mTORC1 selects its substrates, how its kinase activity is controlled, and how it is activated by cancer-associated mutations.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / chemistry
  • Adaptor Proteins, Signal Transducing / metabolism*
  • Amino Acid Motifs
  • Binding Sites
  • Biocatalysis
  • Catalytic Domain
  • Cryoelectron Microscopy*
  • Crystallography, X-Ray
  • Enzyme Activation
  • Humans
  • Mechanistic Target of Rapamycin Complex 1 / agonists
  • Mechanistic Target of Rapamycin Complex 1 / antagonists & inhibitors
  • Mechanistic Target of Rapamycin Complex 1 / chemistry*
  • Mechanistic Target of Rapamycin Complex 1 / ultrastructure*
  • Models, Molecular
  • Mutation
  • Neoplasms / genetics
  • Protein Binding
  • Protein Domains
  • Ras Homolog Enriched in Brain Protein / chemistry
  • Ras Homolog Enriched in Brain Protein / metabolism*
  • Ras Homolog Enriched in Brain Protein / ultrastructure
  • Regulatory-Associated Protein of mTOR / chemistry
  • Regulatory-Associated Protein of mTOR / metabolism
  • Ribosomal Protein S6 Kinases, 70-kDa / metabolism
  • Signal Transduction
  • Sirolimus / metabolism
  • Substrate Specificity
  • Tacrolimus Binding Protein 1A / metabolism


  • AKT1S1 protein, human
  • Adaptor Proteins, Signal Transducing
  • RHEB protein, human
  • RPTOR protein, human
  • Ras Homolog Enriched in Brain Protein
  • Regulatory-Associated Protein of mTOR
  • Mechanistic Target of Rapamycin Complex 1
  • Ribosomal Protein S6 Kinases, 70-kDa
  • ribosomal protein S6 kinase, 70kD, polypeptide 1
  • Tacrolimus Binding Protein 1A
  • Sirolimus