The "two-state folder" MerP forms partially unfolded structures that show temperature dependent hydrogen exchange

Area of Science:

• Protein folding dynamics
• Biophysical chemistry
• Structural biology

Background:

• The protein MerP, a 72 amino acid protein, is typically studied using fluorescence and circular dichroism (CD), which suggest a two-state folding model.
• Understanding protein folding pathways is crucial for comprehending protein function and dysfunction.

Purpose of the Study:

• To investigate the folding energy landscape of the MerP protein.
• To determine the thermodynamic parameters (DeltaG, DeltaH, DeltaC(p)) governing MerP's conformational changes.
• To reconcile discrepancies between traditional probes and hydrogen exchange data.

Main Methods:

• Native state hydrogen exchange monitored across a temperature range of 7-55°C.
• Analysis of temperature dependence of hydrogen exchange to derive thermodynamic values.
• Comparison with data from traditional biophysical probes like fluorescence and CD.

Main Results:

• Hydrogen exchange analysis reveals a complex energy landscape for MerP, deviating from a simple two-state model.
• Evidence suggests the presence of an ensemble of partially unfolded intermediate structures.
• Thermodynamic parameters (DeltaG, DeltaH, DeltaC(p)) were determined for hydrogen exchange processes.
• Amino acid-level stability analysis indicates a broad distribution throughout the protein.

Conclusions:

• MerP's folding pathway is more intricate than previously assumed, involving multiple intermediate states.
• Partially unfolded structures identified through hydrogen exchange likely contribute to MerP's slow folding rate.
• Hydrogen exchange is a powerful technique for uncovering complex protein folding dynamics.