Structural basis of the Axin-adenomatous polyposis coli interaction

Area of Science:

• Molecular Biology
• Cell Signaling
• Structural Biology

Background:

• Axin and adenomatous polyposis coli (APC) are key regulators in the Wnt/Wingless signaling pathway.
• They form a complex with beta-catenin and GSK3beta to control cytoplasmic beta-catenin levels in the absence of Wnt signal.
• Defects in APC, particularly loss of the Axin-binding site, are linked to human cancers.

Purpose of the Study:

• To elucidate the structural basis of the interaction between Axin and APC.
• To understand how this interaction contributes to beta-catenin regulation.
• To provide insights into the evolutionary conservation of Axin and APC.

Main Methods:

• Protease-resistant domain of Axin and an Axin-binding sequence from APC were used.
• Crystal structures of the Axin domain alone and in complex with the APC sequence were determined.

Main Results:

• The Axin-APC interaction occurs at a conserved groove on the Axin protein.
• This binding site is distinct from the G-protein interface found in classical RGS proteins.
• The observed molecular interactions explain the evolutionary conservation of both Axin and APC.

Conclusions:

• The structural analysis reveals the specific interface for Axin-APC complex formation.
• This interaction is crucial for the regulation of beta-catenin, a proto-oncogene.
• The findings offer a molecular explanation for the conservation of these critical proteins in signaling pathways.