Parallel and Sequential Pathways of Molecular Recognition of a Tandem-Repeat Protein and Its Intrinsically Disordered...

Area of Science:

• Molecular Biology
• Biochemistry

Background:

• The Wnt signaling pathway regulates crucial cellular processes like proliferation and differentiation.
• Beta-catenin is a key signal transducer in the Wnt pathway, interacting with transcription factors.
• TCF7L2 is an intrinsically disordered transcription factor involved in Wnt signaling.

Purpose of the Study:

• To investigate the interaction kinetics between beta-catenin and TCF7L2.
• To elucidate the binding mechanism and conformational dynamics of the TCF7L2-beta-catenin complex.
• To understand how TCF7L2's disordered nature influences its interaction with beta-catenin.

Main Methods:

• Engineered a fluorescence reporter system to measure association and dissociation rate constants.
• Utilized site-directed mutagenesis to probe specific regions of TCF7L2.
• Analyzed kinetic data to determine binding mechanisms and conformational effects.

Main Results:

• TCF7L2 and beta-catenin exhibit rapid association and slow, biphasic dissociation kinetics.
• Mutations in fixed TCF7L2 subdomains significantly affected dissociation, while mutations in the labile linker had minimal impact.
• A two-site avidity binding mechanism involving a "fuzzy" complex was proposed.
• Specific mutations revealed alternative dissociation pathways for TCF7L2.

Conclusions:

• The interaction between intrinsically disordered TCF7L2 and beta-catenin is governed by a complex kinetic mechanism.
• Binding involves transient contacts and conformational flexibility, particularly in the TCF7L2 linker region.
• This study provides insights into molecular recognition involving disordered proteins and extended protein surfaces.