Architecture of the Tuberous Sclerosis Protein Complex

Area of Science:

• Structural biology
• Cellular signaling
• Molecular mechanisms

Background:

• The Tuberous Sclerosis Complex (TSC) protein complex (TSCC), comprising TSC1, TSC2, and TBC1D7, integrates cell growth and stress signals upstream of mTORC1.
• TSCC functions as a GTPase-activating protein (GAP) for Rheb, negatively regulating mTORC1 activity.
• Mutations in TSC1 and TSC2 are linked to the genetic disorder tuberous sclerosis.

Purpose of the Study:

• To determine the high-resolution structure and organization of the complete human TSCC.
• To elucidate the molecular architecture and understand the functional implications of TSCC assembly.

Main Methods:

• Single-particle cryo-electron microscopy (cryo-EM) was employed to visualize the human TSCC.
• Detailed structural analysis was performed to dissect the complex's architecture and subunit interactions.

Main Results:

• The human TSCC adopts an elongated, scorpion-like structure with distinct 'body', 'pincer', and 'tail' regions.
• The structure reveals the flexible TSC2 HEAT repeat dimer forming the body, with the TSC1 coiled-coil backbone breaking its symmetry.
• The TSC2 GAP domains are positioned to bind Rheb, suggesting a mechanism for mTORC1 inhibition.

Conclusions:

• The cryo-EM structure provides unprecedented insight into the TSCC's molecular organization and Rheb recruitment mechanism.
• The findings illuminate how TSCC regulates mTORC1 signaling and offer a structural basis for understanding tuberous sclerosis pathogenesis.
• The study hints at higher-order oligomerization, potentially crucial for Rheb-signaling suppression.