Elucidating quantitative stability/flexibility relationships within thioredoxin and its fragments using a distance...

Area of Science:

• Protein Folding Dynamics
• Computational Biophysics
• Molecular Recognition

Background:

• Understanding protein stability and flexibility is crucial for elucidating biological function.
• Escherichia coli thioredoxin (Trx) is a key protein involved in redox homeostasis.
• Previous studies have explored Trx structure-function relationships, but detailed folding pathways remain elusive.

Purpose of the Study:

• To quantitatively determine stability/flexibility relationships in Escherichia coli thioredoxin (Trx) and its fragments.
• To elucidate the folding and unfolding pathways of Trx using computational modeling.
• To investigate the role of molecular cooperativity and intermediate states in Trx function.

Main Methods:

• Utilized a minimal distance constraint model (DCM) for quantitative analysis.
• Employed an exhaustive computational procedure to break hydrogen bonds and simulate fragment dissociation.
• Generated one-dimensional free energy landscapes as a function of global flexibility.

Main Results:

• Trx exhibits a low-barrier, two-state folding process with a voluminous transition state.
• A stable core structure (residues 22-90) was identified as a potential kinetic trap.
• Computational predictions for Trx fragments align with experimental observations of disorder and reconstitution.

Conclusions:

• The study reveals a hierarchical unfolding pathway for Trx, leading to a metastable molten globule intermediate.
• Native state cooperativity analysis highlights flexible regions crucial for catalytic activity.
• Findings support the identification of a 'slow intermediate state' in Trx folding kinetics and suggest Trx can function in partially unfolded states.