Molecular Basis of the Rapamycin Insensitivity of Target Of Rapamycin Complex 2

Abstract

Target of Rapamycin (TOR) plays central roles in the regulation of eukaryote growth as the hub of two essential multiprotein complexes: TORC1, which is rapamycin-sensitive, and the lesser characterized TORC2, which is not. TORC2 is a key regulator of lipid biosynthesis and Akt-mediated survival signaling. In spite of its importance, its structure and the molecular basis of its rapamycin insensitivity are unknown. Using crosslinking-mass spectrometry and electron microscopy, we determined the architecture of TORC2. TORC2 displays a rhomboid shape with pseudo-2-fold symmetry and a prominent central cavity. Our data indicate that the C-terminal part of Avo3, a subunit unique to TORC2, is close to the FKBP12-rapamycin-binding domain of Tor2. Removal of this sequence generated a FKBP12-rapamycin-sensitive TORC2 variant, which provides a powerful tool for deciphering TORC2 function in vivo. Using this variant, we demonstrate a role for TORC2 in G2/M cell-cycle progression.

mTOR in health and in sickness

“…Low-resolution 3D cryo-EM structures of mTORC1 and TORC2 in yeast have also been reported [21,22]. These structures confirm that both complexes are dimers and show that they form a rhomboid shape with a central cavity.…”

TOR Signaling in Budding Yeast

“…TORC2 contains Tor2, in which the FRB domain exists; however, this TOR complex is not sensitive to rapamycin. This issue was resolved using crosslinking-mass spectrometric and electron microscopic analyses, that is, the C-terminal part of Avo3 was close to the FRB domain, which rendered the Fpr1-rapamycin complex incapable of accessing the FRB domain, resulting in TORC2 insensitivity to rapamycin [25].…”

“…The CRIM (conserved region in the middle) domain exists in proximity to the N-terminal side of RBD and has been implicated in binding to the substrates of TORC2 [73,74]. Avo1 binds to the kinase domain of Tor2 via Lst8 [25].…”

“…Although Bit61 binds to TORC2 through Avo1 and Avo3, it is not an essential subunit for the assembly of TORC2 [25,75]. The specific functions of Bit61 have not yet been elucidated; however, mammalian orthologs of Bit61 and Bit2 exist (PRR5 also known as Protor-1, and PRR5L also known as Protor-2) and possess an HbrB domain that was found in a fungal Aspergillus nidulans protein required for filamentous growth [77].…”

Sıçanlarda Rapamisinin Maternal Agresyon Üzerine Etkisi

“…mTOR consists two multi-protein complexes defined as distinct protein binding partners with Rapamycin (Sirolimus). The first complex is mTORC1, which is known mTOR's rapamycin sensitive complex, and the other one is mTORC2, which is largely insensitive to rapamycin [6] . In studies about the mTOR's effect on the nervous system by using the mTOR inhibitors like rapamycin, it has been shown that mTOR is very important for the development of the central nervous system's cell survival, differentiation, axonal development, synaptogenesis; in adult synaptic plasticity, such as long-term potentiation which plays an important role in the process of learning and memory in hippocampus [7][8][9][10] .…”