mTORC2 can associate with ribosomes to promote cotranslational phosphorylation and stability of nascent Akt polypeptide.
The mechanisms that couple translation and protein processing are poorly understood in higher eukaryotes. Although mammalian target of rapamycin (mTOR) complex 1 (mTORC1) controls translation initiation, the function of mTORC2 in protein synthesis remains to be defined. In this study, we find that mTORC2 can colocalize with actively translating ribosomes and can stably interact with rpL23a, a large ribosomal subunit protein present at the tunnel exit. Exclusively during translation of Akt, mTORC2 mediates phosphorylation of the nascent polypeptide at the turn motif (TM) site, Thr450, to avoid cotranslational Akt ubiquitination. Constitutive TM phosphorylation occurs because the TM site is accessible, whereas the hydrophobic motif (Ser473) site is concealed in the ribosomal tunnel. Thus, mTORC2 can function cotranslationally by phosphorylating residues in nascent chains that are critical to attain proper conformation. Our findings reveal that mTOR links protein production with quality control.
Department of Physiology and Biophysics, UMDNJ-Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA.
Won Jun
WJ
Oh
Chang-chih
CC
Wu
Sung Jin
SJ
Kim
Valeria
V
Facchinetti
Louis-André
LA
Julien
Monica
M
Finlan
Philippe P
PP
Roux
Bing
B
Su
Estela
E
Jacinto
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000378:metabolism; D010766:Phosphorylation; D014176:Protein Biosynthesis; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D012269:Ribosomal Proteins / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D054875:Ubiquitination
D046912:Multiprotein Complexes; D012269:Ribosomal Proteins; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases