Unraveling C‑Peptide's Role in MIDY: A Structural Perspective.

Area of Science:

• Biochemistry
• Molecular Biology
• Computational Biology

Background:

• Proinsulin folding is crucial for proper insulin production.
• Mutations in the INS gene cause Wolfram syndrome (MIDY), a form of diabetes.
• The C-peptide plays a dynamic role in guiding proinsulin folding.

Purpose of the Study:

• To map the free-energy landscapes of wild-type (WT) proinsulin and seven MIDY variants.
• To understand how single-residue substitutions affect proinsulin folding dynamics.
• To link specific mutations to altered folding pathways and aggregation risk.

Main Methods:

• Metadynamics and molecular dynamics simulations were used to analyze conformational free-energy landscapes.
• Structural analyses were performed to examine protein-protein interactions and secondary structures.
• Per-residue energy decomposition identified key interactions and energy hotspots.

Main Results:

• Wild-type proinsulin exhibits stable, compact conformations.
• MIDY mutants showed a spectrum of destabilization, from near-WT stability to significant population of misfolded states.
• Mutations disrupted native A-C chain docking, forming non-native B-C interactions and rigidifying the C-peptide.

Conclusions:

• A continuum of destabilization exists for MIDY mutants, linking mutations to altered folding landscapes.
• The C-peptide acts as a dynamic linchpin in proinsulin folding.
• Restoring flexible C-peptide docking may offer a therapeutic strategy for MIDY.