Mechanistic target of rapamycin (mTOR) complex 2 (mTORC2) plays an essential role in regulating cell proliferation through phosphorylating AGC protein kinase family members, including AKT, PKC and SGK1. The functional core complex consists of mTOR, mLST8, and two mTORC2-specific components, Rictor and mSinl. Here we investigated the intermolecular interactions within mTORC2 complex and determined its cryo-electron microscopy structure at 4.9 A resolution. The structure reveals a hollow rhombohedral fold with a 2-fold symmetry. The dimerized mTOR serves as a scaffold for the complex assembly. The N-terminal half of Rictor is composed of helical repeat clusters and binds to mTOR through multiple contacts. mSinl is located close to the FRB domain and catalytic cavity of mTOR. Rictor and mSinl together generate steric hindrance to inhibit binding of FKBP12-rapamycin to mTOR, revealing the mechanism for rapamycin insensitivity of mTORC2. The mTOR dimer in mTORC2 shows more compact conformation than that of mTORC1 (rapamycin sensitive), which might result from the interaction between mTOR and Rictor-mSinl. Structural comparison shows that binding of Rictor and Raptor (mTORC1-specific component) to mTOR is mutually exclusive. Our study provides a basis for understanding the assembly of mTORC2 and a framework to further characterize the regulatory mechanism of mTORC2 pathway.
28
We thank Center of Cryo-Electron Microscopy, Zhejiang University School of Medicine, Center for Biological Imaging of Institute of Biophysics lBP of Chinese Academy of Sciences;National Center for Protein Science Shanghai NCPSS for the support on cryo-EM data collection and analyses. We thank the staff members at Biomedical Core Facility, Fudan University and NCPSS for their help with mass spectrometry analyses. This work was supported by the Ministry of Science and Tech2016YFA0500700, 2016YFA0501100;the National Natural Science Foundation of China31770781, U1432242, 31425008, 91419301;the National Program for support of Top-Notch Young Professionals;the Strategic Priority Research Program of CASXDB08000000
