An isoleucine zipper peptide forms a native-like triple stranded coiled coil in solution

Area of Science:

• Biochemistry
• Structural Biology
• Protein Engineering

Background:

• De novo protein design aims to create novel proteins with specific structures and functions.
• Achieving native-like structural uniqueness is a key challenge in designing self-assembling protein structures.
• Coiled coils are common protein structural motifs formed by alpha-helices.

Purpose of the Study:

• To design and characterize an isoleucine zipper peptide that forms a parallel triple-stranded coiled coil.
• To investigate the role of beta-branched isoleucine residues in achieving native-like structural uniqueness.
• To confirm the stability and structural integrity of the designed coiled coil.

Main Methods:

• Peptide design incorporating beta-branched isoleucine residues at the hydrophobic interface.
• Circular dichroism (CD) spectroscopy to assess secondary structure and stability.
• Sedimentation equilibrium ultracentrifugation to determine molecular weight and assembly state.
• Fluorescence quenching assays with acridine to probe peptide orientation.
• Proton-deuterium amide hydrogen exchange and hydrophobic dye binding assays to evaluate structural uniqueness.

Main Results:

• The designed isoleucine zipper peptide successfully formed a stable triple-stranded coiled coil.
• Circular dichroism and sedimentation equilibrium confirmed the formation of a stable, triple-stranded structure.
• Fluorescence quenching indicated a parallel orientation of the peptides within the coiled coil.
• Proton-deuterium exchange rates were significantly slower than expected for global unfolding, suggesting a well-protected structure.
• Hydrophobic dye binding assays showed no significant binding, consistent with a tightly packed hydrophobic core.

Conclusions:

• Beta-branched isoleucine residues in the hydrophobic interface enhance side chain packing in designed coiled coils.
• The designed peptide adopts a stable, triple-stranded coiled coil structure with native-like structural uniqueness.
• This study demonstrates a strategy for creating de novo protein structures that mimic the stability and packing of natural proteins.