Nativelike structure in designed four alpha-helix bundles driven by buried polar interactions

Area of Science:

• Protein engineering
• Structural biology
• Biochemistry

Background:

• Helical bundle proteins rely on specific packing for their structure.
• Traditional protein design often focuses on hydrophobic complementarity ("knobs in holes").

Purpose of the Study:

• To investigate if polar interactions can drive structural specificity in helical bundle proteins.
• To demonstrate ligand-induced control over protein structure.
• To explore simplified protein design strategies.

Main Methods:

• Designing helical bundle proteins with specific polar interactions.
• Utilizing histidine-binding cofactors of varying shapes to probe the protein core.
• Inducing structural changes by ligating cofactors that bind one or two histidine ligands.

Main Results:

• A single internal polar interaction per helix is sufficient to confer structural specificity.
• Structural specificity is independent of traditional "knobs in holes" packing.
• Protein structure can be reversibly switched on and off by cofactor ligation.
• Proteins were designed without computational modeling, simplifying the design process.

Conclusions:

• Polar interactions are a key determinant of structural specificity in helical bundles.
• Ligand binding offers extensive control over protein architecture.
• Protein design can be achieved through simpler, polar-interaction-based strategies, bypassing complex hydrophobic packing requirements.
• This work has implications for self-assembled molecular systems and protein engineering.