Research Article

Structural basis for the docking of mTORC1 on the lysosomal surface

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Science  25 Oct 2019:
Vol. 366, Issue 6464, pp. 468-475
DOI: 10.1126/science.aay0166

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Complex regulation

The protein kinase mTORC1 controls cellular growth in response to external signals. In the presence of nutrients, it localizes on the surface of the lysosome, where it is activated. The Raptor domain of mTORC1 binds to a complex comprising the protein Ragulator and a heterodimer of the Rag guanosine triphosphatase, which can adopt four different nucleotide conformations depending on nutrient availability. Rogala et al. determined the structure of the Raptor-Rag-Ragulator complex at 3.2-angstrom resolution by cryo–electron microscopy. The structure shows why Raptor binds only to a specific nucleotide conformation of the Rag heterodimer and suggests a model for how mTORC1 would dock onto the lysosomal surface, which is a key step in its activation.

Science, this issue p. 468

Abstract

The mTORC1 (mechanistic target of rapamycin complex 1) protein kinase regulates growth in response to nutrients and growth factors. Nutrients promote its translocation to the lysosomal surface, where its Raptor subunit interacts with the Rag guanosine triphosphatase (GTPase)–Ragulator complex. Nutrients switch the heterodimeric Rag GTPases among four different nucleotide-binding states, only one of which (RagA/B•GTP–RagC/D•GDP) permits mTORC1 association. We used cryo–electron microscopy to determine the structure of the supercomplex of Raptor with Rag-Ragulator at a resolution of 3.2 angstroms. Our findings indicate that the Raptor α-solenoid directly detects the nucleotide state of RagA while the Raptor “claw” threads between the GTPase domains to detect that of RagC. Mutations that disrupted Rag-Raptor binding inhibited mTORC1 lysosomal localization and signaling. By comparison with a structure of mTORC1 bound to its activator Rheb, we developed a model of active mTORC1 docked on the lysosome.

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