Cells have internal “growth switches” that respond to nutrient availability—especially amino acids. When food is plentiful, cells accelerate protein synthesis and metabolism; when it is scarce, they slow down. A team from KAIST and Yonsei University reports a molecular explanation for how amino acid signals are converted into mTORC1-dependent growth signaling, offering a potential blueprint for more targeted anticancer strategies.
The central node in this pathway is mTORC1, a protein complex long known to act as the cell’s growth switch. Although direct mTORC1 inhibitors can suppress tumor growth, they may also disrupt normal cellular functions because mTORC1 is required for healthy metabolism. The new work therefore focuses on the earlier steps that sense nutrients and trigger mTORC1, aiming to intervene upstream.
Researchers examined the multi-tRNA synthetase complex (MSC), a large assembly best known for charging tRNAs with amino acids during translation. Using experiments that track MSC behavior after amino acid stimulation, they found that the MSC releases a protein called LARS1. This release provides a mechanistic link between nutrient cues and activation of mTORC1.
LARS1 (leucyl-tRNA synthetase 1) turned out to be more than a translation enzyme: it also functions as an intracellular leucine sensor. Upon nutrient sufficiency, LARS1 undergoes phosphorylation, a chemical modification that changes how proteins interact. Phosphorylation weakens LARS1’s grip on IARS1, the MSC subunit that anchors it.
A “switch model” emerges. In nutrient-poor conditions, LARS1 remains bound within the MSC and the growth signal stays off. When nutrients rise, phosphorylation acts like a deployment signal, causing LARS1 to dissociate from IARS1. Freed LARS1 then activates mTORC1, turning growth back on.
To define this mechanism structurally, the team used cryo-electron microscopy (cryo-EM), generating a near-atomic view of the LARS1:IARS1 complex. The structure revealed how LARS1 and IARS1 normally assemble tightly, and how phosphorylation would disrupt their interface to enable dissociation.
Finally, the researchers engineered phosphomimetic LARS1 variants designed to imitate the phosphorylated state. These mutants significantly boosted mTORC1 activity, supporting the conclusion that LARS1 phosphorylation is the key molecular switch translating amino acid signals into growth signaling.
The study, published online in Nature Communications on June 11, advances a detailed molecular map of nutrient sensing by the MSC. By identifying the steps upstream of mTORC1 activation, it also highlights a route to therapies that may suppress abnormal tumor growth signals without directly shutting down mTORC1 itself.
Subject of Research: Amino acid–responsive nutrient sensing mechanism linking the MSC to mTORC1 via LARS1 phosphorylation.
Article Title: Cryo-EM structure of the LARS1:IARS1 complex reveals a nutrient-responsive switch controlling mTORC1 signaling
News Publication Date: 11-Jun-2026
Web References: http://dx.doi.org/10.1038/s41467-026-74085-x
References: Nature Communications (published online June 11, 2026). DOI: 10.1038/s41467-026-74085-x.
Image Credits: Credit: KAIST
