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Updated: Aug 6, 2026

Characterization at the Molecular Level using Robust Biochemical Approaches of a New Kinase Protein
Published on: June 30, 2019
mSin1 is necessary for Akt/PKB phosphorylation, and its isoforms define three distinct mTORC2s
Maria A Frias1, Carson C Thoreen, Jacob D Jaffe
1Whitehead Institute for Biomedical Research and Department of Biology, Massachusetts Institute of Technology, Nine Cambridge Center, Cambridge, Massachusetts 02142, USA.
Abstract:
The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that participates in at least two distinct multiprotein complexes, mTORC1 and mTORC2 . These complexes play important roles in the regulation of cell growth, proliferation, survival, and metabolism. mTORC2 is a hydrophobic motif kinase for the cell-survival protein Akt/PKB and, here, we identify mSin1 as a component of mTORC2 but not mTORC1. mSin1 is necessary for the assembly of mTORC2 and for its capacity to phosphorylate Akt/PKB. Alternative splicing generates at least five isoforms of the mSin1 protein , three of which assemble into mTORC2 to generate three distinct mTORC2s. Even though all mTORC2s can phosphorylate Akt/PKB in vitro, insulin regulates the activity of only two of them. Thus, we propose that cells contain several mTORC2 flavors that may phosphorylate Akt/PKB in response to different signals.
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