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The vacuolar protein Pib2 acts as a direct glutamine sensor to activate TORC1 (target of rapamycin complex 1) in yeast. This discovery reveals a novel, Gtr-independent mechanism for nutrient sensing and metabolic control in cells.

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Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • TOR complex 1 (TORC1) regulates cell growth and metabolism in response to nutrients, especially amino acids.
  • While mammalian TORC1 activation involves Rag GTPases and specific sensors, these are not conserved in organisms like yeast.
  • Previous work suggested glutamine activates yeast TORC1 via a Gtr-independent pathway involving vacuolar protein Pib2, but the sensor and mechanism were unknown.

Purpose of the Study:

  • To identify the glutamine sensor and elucidate the mechanism of TORC1 activation in yeast.
  • To investigate the role of vacuolar protein Pib2 in sensing glutamine and activating TORC1.

Main Methods:

  • In vitro reconstitution of glutamine-responsive TORC1 activation using purified Pib2 and TORC1.
  • Analysis of glutamine-induced changes in Pib2 folding state.

Main Results:

  • Glutamine-responsive TORC1 activation was successfully reconstituted in vitro with purified Pib2 and TORC1.
  • Glutamine was found to specifically induce a conformational change in the folding state of Pib2.
  • These results identify Pib2 as a direct glutamine sensor.

Conclusions:

  • Pib2 functions as a direct glutamine sensor that activates TORC1 in yeast.
  • This study establishes a novel Gtr-independent mechanism for amino acid sensing and TORC1 regulation.
  • The findings provide a new model for understanding metabolic control in yeast and other organisms.