Crystal structure of a Tankyrase-Axin complex and its implications for Axin turnover and Tankyrase substrate...

Area of Science:

• Biochemistry
• Structural Biology
• Cancer Biology

Background:

• Axin acts as a tumor suppressor by negatively regulating the Wnt/β-catenin pathway.
• Tankyrase (TNKS) controls Axin levels via poly-ADP-ribosylation, necessitating Axin-TNKS interaction.
• This interaction is a potential therapeutic target for cancers and other diseases involving β-catenin.

Purpose of the Study:

• To determine the crystal structure of a mouse TNKS1 fragment (ARC2-3) complexed with the Axin1 binding domain.
• To elucidate the structural basis of the TNKS-Axin interaction and its role in Axin regulation.

Main Methods:

• X-ray crystallography of mouse TNKS1 ARC2-3 and Axin1 binding domain complex.
• Site-directed mutagenesis of TNKS and Axin1 to assess binding and functional consequences.
• Cellular assays to evaluate Axin stabilization upon mutation.

Main Results:

• The crystal structure revealed Axin binds TNKS via two distinct segments simultaneously to the TNKS ARC2-3 homodimer.
• A conserved glycine residue in each Axin segment forms a critical 'glycine-selection gate' with TNKS tyrosine residues.
• Mutations in the gate or Axin glycine residues abolished binding and led to Axin stabilization in cells, indicating bivalent binding is essential for Axin turnover.

Conclusions:

• The study reveals a novel bivalent binding mode of Axin to TNKS through a glycine-selection gate.
• This structural insight clarifies TNKS substrate recruitment and provides a basis for developing specific Wnt/β-catenin signaling inhibitors.
• Understanding the TNKS-Axin interaction mechanism is key for therapeutic strategies targeting related diseases.