Structure of the Human mTOR Complex I and Its Implications for Rapamycin Inhibition

Abstract

Summary The mammalian Target of Rapamycin Complex 1 (mTORC1) regulates cell growth in response to the nutrient and energy status of the cell, and its deregulation is common in human cancers. Little is known about the overall architecture and subunit organization of this essential signaling complex. We have determined the three-dimensional (3D) structure of the fully assembled human mTORC1 by cryo-electron microscopy (cryo-EM). Our analyses reveal that mTORC1 is an obligate dimer with an overall rhomboid shape and a central cavity. The dimeric interfaces are formed by interlocking interactions between the mTOR and raptor subunits. Extended incubation with FKBP12-rapamycin compromises the structural integrity of mTORC1 in a stepwise manner, leading us to propose a model in which rapamycin inhibits mTORC1-mediated phosphorylation of 4E-BP1 and S6K1 through different mechanisms.

Structural insights of mTOR complex 1

“…To complement the reconstruction of mTORC1, the authors also resolved the structure of the fungus Chaetomium thermophilum Raptor (CtRaptor), which exhibits 44% sequence identity to human Raptor. The overall shape of the reconstruction agrees with that observed by low-resolution cyro-EM [4]; however, it appears that the handedness of the previous reconstruction was not assigned correctly. Generally, mTORC1 adopts a cage-like, dimeric architecture and appears in a hollow lozenge shape, in which Raptor and mLST8 contribute peripheral parts of the complex and make up the pinnacles of the longer and shorter axes of the lozenge, respectively.…”

“…Cryo-electron microscopy (cryo-EM) studies have shown that mTOR forms an obligate dimer with an overall rhomboid shape and a central cavity [4]. However, the reliability of the handedness of the reconstruction and the position of individual subunits was significantly compromised due to the low-resolution (26 Å) reconstruction.…”

mTOR-Dependent Cell Survival Mechanisms

“…Regulatory-associated protein of mTOR (RAPTOR) and 40-kDa pro-rich Akt-substrate (PRAS40) are unique to mTORC1, whereas rapamycin-insensitive companion of mTOR (RICTOR), mammalian stressed-activated map-kinase interacting protein 1 (mSIN1), and protein observed with RICTOR (PROTOR) are specific to mTORC2. Recent work is beginning to reveal insight into the structure of mTORC1 (Yip et al 2010). A cryo-EM structure of mTORC1 at 26 Å indicates that the complex is a dimer with interlocking mTOR-RAPTOR interactions and where PRAS40 acts as a competitive inhibitor for the binding of mTORC1 substrates to RAPTOR (Wang et al 2008;Yip et al 2010).…”

“…Recent work is beginning to reveal insight into the structure of mTORC1 (Yip et al 2010). A cryo-EM structure of mTORC1 at 26 Å indicates that the complex is a dimer with interlocking mTOR-RAPTOR interactions and where PRAS40 acts as a competitive inhibitor for the binding of mTORC1 substrates to RAPTOR (Wang et al 2008;Yip et al 2010). mLST8 associates with the mTOR kinase domain, located in the carboxyl terminus (Kim et al 2003).…”

“…mLST8 associates with the mTOR kinase domain, located in the carboxyl terminus (Kim et al 2003). In the presence of rapamycin, the mTOR-mLST8 interaction is stable, whereas the drug weakens the mTOR-RAPTOR interaction (Kim and Sabatini 2004;Yip et al 2010). The structure of mTORC2 remains a mystery.…”