Mechanisms of mTORC1 activation by RHEB and inhibition by PRAS40

Haijuan Yang, Xiaolu Jiang, Buren Li, Hyo J. Yang, Meredith Miller, Angela Yang, Ankita Dhar and Nikola P. Pavletich ()
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Haijuan Yang: Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York
Xiaolu Jiang: Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York
Buren Li: Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York
Hyo J. Yang: Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York
Meredith Miller: Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York
Angela Yang: Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York
Ankita Dhar: Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York
Nikola P. Pavletich: Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York

Nature, 2017, vol. 552, issue 7685, 368-373

Abstract: Abstract 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.

Date: 2017
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DOI: 10.1038/nature25023

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