How leucine and arginine reach the mTORC1 switch
mTORC1 is a protein-kinase complex that integrates nutrient and growth signals to decide whether a cell builds proteins and grows. Among its inputs are specific amino acids. Leucine is sensed by Sestrin2 and arginine by CASTOR1; when these amino acids are present, the sensors release their inhibition of the GATOR2 complex. That relieves GATOR1's suppression of the Rag GTPases.
Active Rag GTPases then recruit mTORC1 to the surface of the lysosome, the cellular compartment where it can be switched on by the small GTPase Rheb. Anchoring at the lysosome is the step that physically positions mTORC1 for activation.
Why this pathway draws so much research interest
Because mTORC1 governs protein synthesis, autophagy, and cell growth, the amino-acid sensing arm is studied in contexts ranging from muscle building to aging and cancer biology. Much of the detailed sensor mechanism comes from cell and animal models, and how cleanly it maps onto everyday human nutrition is still an active question.
This describes a molecular signaling pathway for educational purposes and is not a basis for any supplement or treatment decision; consult a qualified professional for those.