Abstract by William Ludlam
Chemistry and Biochemistry
Structure of the mLST8-CCT Folding Intermediate
The mechanistic target of rapamycin (mTOR) kinase is a master regulator of eukaryotic cell metabolism, growth and survival. mTOR functions in two distinct complexes, called mTORC1 and mTORC2. While mTORC functions have been studied extensively, little is known about how the individual subunits of these complexes are assembled from their nascent polypeptide chains. Here, we provide evidence that an important chaperone for cytosolic proteins, the chaperonin containing TCP-1 (CCT), is involved in the folding and assembly of the protein mLST8 (mammalian lethal with SEC13 protein 8), a key component of both mTOR complexes. We have isolated an mLST8 folding intermediate bound to CCT and determined the structure of this complex to 4.4 angstrom resolution by single particle cryo-electron microscopy. This structure represents the highest resolution of a folding substrate inside the CCT cavity to date and shows mLST8 in an unexpected position between the two CCT octamer rings in a near-native conformation.