Structural basis for the assembly of the Ragulator-Rag GTPase complex

Area of Science:

• Cell Biology
• Molecular Biology
• Structural Biology

Background:

• The mechanistic target of rapamycin complex 1 (mTORC1) regulates cell growth and metabolism.
• mTORC1 activity is controlled by Rag GTPases, which localize to lysosomes via the Ragulator complex.
• Ragulator is a pentameric complex including p18/LAMTOR1 and roadblock heterodimers.

Purpose of the Study:

• To elucidate the molecular basis of Rag GTPase regulation by determining the structure of Ragulator.
• To understand the role of p18 in assembling the Ragulator-Rag GTPase complex on lysosomes.
• To investigate the mechanism of amino acid-dependent mTORC1 activation.

Main Methods:

• X-ray crystallography to determine the structure of Ragulator in complex with Rag GTPase roadblock domains.
• Cellular assays to assess the requirement of p18 for complex assembly and mTORC1 activation.
• In vitro biochemical analyses to confirm functional roles.

Main Results:

• The crystal structure reveals how p18 organizes roadblock heterodimers to assemble onto lysosomes.
• p18 acts as a scaffold, wrapping around and tandemly assembling roadblock heterodimers.
• p18 is essential for Ragulator-Rag GTPase complex formation and nutrient-dependent mTORC1 activation.

Conclusions:

• p18 is a critical organizing scaffold for the Ragulator-Rag GTPase complex on lysosomes.
• This complex serves as a platform for nutrient sensing, regulating mTORC1.
• The findings provide molecular insights into nutrient-mediated regulation of cell growth.