Structural and functional analysis of the role of the chaperonin CCT in mTOR complex assembly
Three views of the 3D reconstruction of the CCT:mLST8 complex obtained by cryoelectron microscopy. Left, sive view. Center, a sliced view with the client protein, the WD40 protein mLST8 (in red) bound to the central part of the CCT two-ring structure. Right, and end-on view of the complex
Cuellar J, Ludlam WG, Tensmeyer NC, Aoba T, Dhavale M, Santiago C, Bueno-Carrasco MT, Mann MJ, Plimpton RL, Makaju A, Franklin S, Willardson BM, Valpuesta JM.
Nat Commun 2019 Jun; 10: 2865.
The mechanistic target of rapamycin (mTOR) kinase forms two multi-protein signaling complexes, mTORC1 and mTORC2, which are master regulators of cell growth, metabolism, survival and autophagy. Two of the subunits of these complexes are mLST8 and Raptor, beta-propeller proteins that stabilize the mTOR kinase and recruit substrates, respectively. Here we report that the eukaryotic chaperonin CCT plays a key role in mTORC assembly and signaling by folding both mLST8 and Raptor. A high resolution (4.0 A) cryo-EM structure of the human mLST8-CCT intermediate isolated directly from cells shows mLST8 in a near-native state bound to CCT deep within the folding chamber between the two CCT rings, and interacting mainly with the disordered N- and C-termini of specific CCT subunits of both rings. These findings describe a unique function of CCT in mTORC assembly and a distinct binding site in CCT for mLST8, far from those found for similar beta-propeller proteins.
PubMed: 31253771. Doi: 10.1038/s41467-019-10781-1. OPEN Free PMC
