Structural basis for leucine sensing by the Sestrin2-mTORC1 pathway

Area of Science:

• Molecular Biology
• Cellular Biology
• Structural Biology

Background:

• The mechanistic target of rapamycin complex 1 (mTORC1) regulates eukaryotic cell growth in response to nutrient availability.
• Leucine is a critical amino acid that activates mTORC1 signaling through the Rag GTPases, GATOR1, and GATOR2.
• Sestrin2 functions as a leucine sensor by interacting with GATOR2.

Purpose of the Study:

• To determine the crystal structure of Sestrin2 in complex with leucine.
• To elucidate the structural basis of leucine recognition and binding by Sestrin2.
• To understand the mechanism by which Sestrin2 senses leucine for mTORC1 pathway activation.

Main Methods:

• X-ray crystallography to determine the 2.7 angstrom structure of Sestrin2-leucine complex.
• Site-directed mutagenesis to generate structure-guided mutants of Sestrin2.
• Cellular assays to assess the impact of mutations on leucine-induced mTORC1 activation.

Main Results:

• The crystal structure reveals a single binding pocket in Sestrin2 that accommodates leucine, coordinating its charged groups and hydrophobic side chain.
• A flexible loop forms a lid-latch mechanism essential for leucine binding.
• A structure-guided mutation reducing Sestrin2's leucine affinity increased the cellular leucine concentration required for mTORC1 activation.

Conclusions:

• Sestrin2 binds leucine via a specific pocket employing a lid-latch mechanism.
• This structural insight provides a mechanistic understanding of amino acid sensing in the mTORC1 pathway.
• The findings link Sestrin2 structure to cellular nutrient-sensing and growth regulation.