Abstract by Blake Nordblad
Chemistry and Biochemistry
Isolation of the mLST8-CCT Intermediate in the Assembly of mTOR Complexes
The mechanistic target of rapamycin (mTOR) kinase plays a key role in regulating cell growth and metabolism. mTOR complexes with other protein subunits to form two distinct complexes, mTORC1 and mTORC2. The mTOR complexes have been studies extensively; however, little is known about the assembly of the subunits into the mTOR complex. We have found that the chaperonin containing TCP-1 (CCT) is integral to the folding and assembly of one of the mTORC subunits mLST8 (mammalian lethal with SEC13 protein 8). To understand how CCT folds mLST8, we have isolated an mLST8 folding intermediate bound to CCT and solved the structure of the complex using cryo-electron microscopy (cryo-EM) to 4.4 Å resolution. The structure shows mLST8 in a near-native conformation sitting between the two CCT octameric rings and interacting with the N- and C-termini of the CCT subunits. A CCT folding substrate has never been observed between the rings, which suggests a novel mechanism for CCT to bind and fold mLST8.