Structure of TOR and Its Complex with KOG1

Abstract

The target of rapamycin (TOR) is a large (281 kDa) conserved Ser/Thr protein kinase that functions as a central controller of cell growth. TOR assembles into two distinct multiprotein complexes: TORC1 and TORC2. A defining feature of TORC1 is the interaction of TOR with KOG1 (Raptor in mammals) and its sensitivity to a rapamycin-FKBP12 complex. Here, we have reconstructed in three dimensions the 25 A resolution structures of endogenous budding yeast TOR1 and a TOR-KOG1 complex, using electron microscopy. TOR features distinctive N-terminal HEAT repeats that form a curved tubular-shaped domain that associates with the C-terminal WD40 repeat domain of KOG1. The N terminus of KOG1 is in proximity to the TOR kinase domain, likely functioning to bring substrates into the vicinity of the catalytic region. A model is proposed for the molecular architecture of the TOR-KOG1 complex explaining its sensitivity to rapamycin.

Not all substrates are treated equally: Implications for mTOR, rapamycin-resistance, and cancer therapy

“…First, KOG1's C-terminal WD40 domain interacts with TOR's N-terminal domain, and second, KOG1's N-terminal RNC domain interacts with TOR's kinase domain. 20 Interestingly, the N-terminal region of Raptor is necessary for Raptor-S6K1 interaction via the TOS motif, suggesting that Raptor may bring substrates near mTOR's kinase domain for phosphorylation. 17 Whether the TOS motif directly interacts with the N-terminus of Raptor remains to be determined.…”

Mammalian Target of Rapamycin Complex 1 (mTORC1) Activity Is Associated with Phosphorylation of Raptor by mTOR

“…All these sites are located in the region between the N-terminal conserved region and the C-terminal seven WD repeats. The raptor C terminus tightly interacts with mTOR (8,26), and the N-terminal conserved region is suggested to bind to the TOS motif in substrates such as S6K1 and 4E-BP1 (27). Mutation of raptor at Ser 863 did not change raptor binding to 4E-BP1 as measured by interaction with 4E-BP1 recombinant protein-coupled beads.…”

Rheb in neuronal degeneration, regeneration, and connectivity

“…mTOR (frequently quoted as 'mechanistic' target of rapamycin), is an evolutionarily conserved checkpoint protein kinase that has emerged as a major effector of cell growth and proliferation. The mTOR pathway regulates protein synthesis, autophagy and metabolism in response to secreted growth factors, cellular levels of amino acids, glucose, energy levels, and oxygen levels Hay and Sonenberg, 2004;Adami et al, 2007;Swiech et al, 2008;Laplante and Sabatini, 2012). The mTOR forms two distinct complexes, mTORC1 and mTORC2, which are functionally different (Loewith et al, 2002).…”

“…The mTOR forms two distinct complexes, mTORC1 and mTORC2, which are functionally different (Loewith et al, 2002). mTORC1 consists of mTOR, regulatory-associated protein of mTOR (Raptor); and mammalian lethal with SEC13 protein 8 (mLST8), along with two endogenous inhibitors of the complex, 40 kDa Proline-rich Akt substrate (PRAS40), and DEP domain-containing mTOR-interacting protein (DEPTOR) (Loewith et al, 2002;Hay and Sonenberg, 2004;Long et al, 2005;Yang et al, 2006;Adami et al, 2007). Downstream of activated mTORC1, protein translation is promoted by phosphorylation of 70 kDa ribosomal S6 kinase (S6K) and eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) and autophagy is suppressed via Ulk1/Atg13 (Burnett et al, 1998;Hay and Sonenberg, 2004;Ganley et al, 2009;Hosokawa et al, 2009;Jung et al, 2009;Wang et al, 2009;Sciarretta et al, 2012) (see Figure 1).…”

“…The FKBP12-rapamycin complex then acts on mTOR to inhibit mTORC1 function and thereby inhibit cell growth Loewith et al, 2002;Hay and Sonenberg, 2004;Adami et al, 2007;Gkogkas et al, 2010). mTORC2, in addition to mTOR and mLST8, contains the essential polypeptides: rapamycininsensitive companion of mTOR (rictor) and mammalian stress-activated map kinase-interacting protein 1 (mSin1) (Loewith et al, 2002;Sarbassov et al, 2004;Adami et al, 2007;Avruch and Long, 2009). mTORC2 may signal to the actin cytoskeleton through Rho and Rac (Jacinto et al, 2004;Sarbassov et al, 2004).…”