Some (dis)assembly required: partial unfolding in the Par-6 allosteric switch

Area of Science:

• Molecular Biology
• Structural Biology
• Protein Dynamics

Background:

• Allostery describes functional connections between distant protein sites, crucial for regulating biological processes.
• Par-6 is a scaffold protein essential for establishing and maintaining cell polarity through protein complex organization.
• PDZ domains are versatile protein modules involved in various signaling pathways and protein-protein interactions.

Purpose of the Study:

• To review the conformational dynamics underlying allosteric regulation in the Par-6 PDZ domain.
• To elucidate the role of protein unfolding intermediates in the allosteric switching mechanism of Par-6.
• To explore evolutionary implications of allosteric regulation at domain interfaces and thermodynamic stability.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy to probe protein dynamics and conformational states.
• Thermodynamic and kinetic studies to analyze the energetics and rates of protein conformational changes.
• Analysis of protein structure and evolutionary conservation of key residues and interfaces.

Main Results:

• The Par-6 PDZ domain samples a conserved unfolding intermediate, enabling loop rearrangements that modulate ligand binding.
• Cdc42 binding to Par-6 induces a novel interface with the CRIB motif, stabilizing the high-affinity PDZ conformation.
• Partial unfolding of the PDZ domain is identified as a critical component of the Par-6 allosteric switching mechanism.

Conclusions:

• Allosteric regulation can arise from interfaces between adjacent domains within the same protein, as exemplified by the Par-6 CRIB-PDZ module.
• Proteins may evolve to reduce thermodynamic stability, favoring the sampling of unfolding intermediates for conformational switching and function.
• Understanding these dynamics provides insights into protein evolution and the mechanisms of allosteric control in signaling pathways.