Intrinsic Disorder in a Well-Folded Globular Protein

Area of Science:

• Protein folding dynamics
• Biophysics
• Computational biology

Background:

• Monellin is a heterodimeric sweet protein that folds upon binding of its two chains.
• Intrinsically disordered proteins (IDPs) that fold upon binding are of significant interest.
• Understanding the folding mechanisms of such proteins is crucial for protein design.

Purpose of the Study:

• To investigate the folding mechanism of a single-chain variant of monellin (scMn).
• To elucidate the role of interchain interactions in the folding process.
• To explore strategies for designing IDPs that fold upon binding.

Main Methods:

• Simulations using an all heavy-atom structure-based model.
• Analysis of folding pathways and transition-state ensembles.
• Computational mutagenesis to study the effect of interchain interactions.

Main Results:

• scMn exhibits cooperative folding, consistent with experimental observations.
• Structure formation is localized to a β2-β3 hairpin at the transition state.
• Early formation of the interchain interface (β2-β3) is energetically favored.
• Disordered states are maintained when the interchain interface is disrupted.

Conclusions:

• The folding of monellin is driven by the early formation of an interchain interface.
• This mechanism allows the individual chains to remain disordered until binding.
• Designing proteins by cleaving globular proteins within their folding nucleus may yield IDPs that fold upon binding.