Transition states for protein folding have native topologies despite high structural variability

Area of Science:

• Structural biology
• Protein folding dynamics
• Biophysics

Background:

• Understanding protein folding is crucial for deciphering biological function and disease mechanisms.
• SH3 domains are model systems for studying protein folding due to their compact structure.
• Transition states represent a critical, yet elusive, stage in the folding pathway.

Purpose of the Study:

• To structurally characterize the folding transition states of three SH3 domains.
• To elucidate the role of secondary structure formation and solvent exclusion in the transition state.
• To investigate the mechanism by which native topology is achieved during folding.

Main Methods:

• Computational structural analysis of folding pathways.
• Comparison of transition state ensemble structures with a database of native protein folds.
• Analysis of residue interactions within the transition state ensemble.

Main Results:

• Transition states exhibit incomplete secondary structure formation.
• Solvent is only partially excluded from the protein interior during the transition state.
• Despite local variability, all analyzed transition state structures possess the characteristic SH3 domain topology.
• A network of hydrophobic interactions appears to guide the generation of native topology.

Conclusions:

• Protein folding likely proceeds through a mechanism where hydrophobic interactions establish the native topology early in the folding process.
• This mechanism allows for high-fidelity folding with reduced reliance on extensive specific interactions during conformational search.
• The findings provide insights into the fundamental principles governing protein structure formation.