The 3.2-Å resolution structure of human mTORC2

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• The mammalian target of rapamycin (mTOR) pathway is crucial for regulating cell growth and is implicated in diseases like cancer and diabetes.
• mTOR functions through two complexes: mTORC1 and mTORC2, with mTORC2's precise mechanisms remaining less understood.
• Understanding mTORC2 structure is vital for deciphering its role in cellular processes and disease.

Purpose of the Study:

• To determine the high-resolution structure of mTORC2 using cryo-electron microscopy (cryo-EM).
• To elucidate the structural basis for mTORC2's rapamycin insensitivity and regulatory mechanisms.
• To identify novel small-molecule binding sites within the mTORC2 complex.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to achieve a 3.2-Å resolution reconstruction of mTORC2.
• Structural analysis to visualize subunit interactions and identify binding pockets.
• Biochemical assays to investigate the functional implications of identified binding sites.

Main Results:

• The cryo-EM reconstruction revealed detailed folds of Rictor and SIN1 subunits within mTORC2.
• The carboxyl-terminal domain of Rictor was identified as responsible for mTORC2's resistance to rapamycin.
• Two novel binding sites were visualized: an inositol hexakisphosphate (InsP6) pocket in mTOR and an mTORC2-specific nucleotide binding site in Rictor.
• Structural and biochemical data suggest these sites are involved in folding or ternary interactions rather than direct activity regulation.

Conclusions:

• The determined structure provides unprecedented insights into mTORC2 assembly and regulation.
• The identification of Rictor's role in rapamycin insensitivity offers a key distinction from mTORC1.
• The novel binding sites present potential targets for future development of mTORC2-specific inhibitors.
• This work lays a foundation for further research into mTORC2 signaling pathways and therapeutic strategies.