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Structural and functional analysis of the role of the chaperonin CCT in mTOR complex assembly

Jorge Cuéllar1, W Grant Ludlam2, Nicole C Tensmeyer2

  • 1Centro Nacional de Biotecnología, Campus de la Universidad Autónoma de Madrid, 28049, Madrid, Spain.

Nature Communications
|June 30, 2019
PubMed

Insights

The eukaryotic chaperonin CCT folds key proteins mLST8 and Raptor, crucial for mechanistic target of rapamycin (mTOR) complex assembly and signaling. This reveals a novel role for CCT in regulating cell growth and metabolism pathways.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Structural Biology

Background:

  • The mechanistic target of rapamycin (mTOR) kinase is central to cell growth, metabolism, survival, and autophagy.
  • mTOR functions via two complexes, mTORC1 and mTORC2.
  • mLST8 and Raptor are key subunits stabilizing mTOR and recruiting substrates.

Purpose of the Study:

  • To investigate the role of the eukaryotic chaperonin CCT in mTORC assembly and signaling.
  • To elucidate the structural basis of CCT's interaction with mTOR subunits.

Main Methods:

  • Cryo-electron microscopy (cryo-EM) at 4.0 Å resolution.
  • Isolation of human mLST8-CCT intermediate directly from cells.

Main Results:

  • Chaperonin CCT plays a critical role in folding both mLST8 and Raptor, essential for mTORC assembly.
  • Cryo-EM revealed mLST8 bound within the CCT folding chamber, interacting with CCT subunit termini.
  • A novel binding site for mLST8 on CCT was identified, distinct from those for other β-propeller proteins.

Conclusions:

  • CCT is a key regulator of mTORC assembly and signaling through its chaperoning of mLST8 and Raptor.
  • The findings uncover a unique function of CCT and a specific mLST8-binding site within the chaperonin.
  • This work provides structural insights into the regulation of fundamental cellular processes controlled by mTOR.

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