Coiled-coil assembly by peptides with non-heptad sequence motifs

Area of Science:

• Structural biology
• Protein biochemistry

Background:

• The seven-residue heptad repeat is the hallmark of coiled coils.
• Extended filamentous proteins exhibit disruptions in heptad patterns called 'skips' and 'stammers', with unclear structural roles.

Purpose of the Study:

• To investigate the structural consequences and roles of sequence variations in extended coiled coils.
• To explore the role of eleven-residue units (hendecads) in protein structure and function.

Main Methods:

• Analysis of a cytoskeleton protein sequence from Giardia lamblia.
• Synthesis and solution-based folding studies of peptides based on a 7-11-7 motif.
• Comparison of experimental data with the coiled-coil model.

Main Results:

• A 7-11-7 motif, featuring heptads flanking hendecads, was identified in a Giardia lamblia cytoskeleton protein.
• Synthetic peptides corresponding to this motif formed stable, fully helical, parallel dimers in solution.
• The observed sequence pattern and experimental folding are consistent with an expanded coiled-coil model, accommodating hendecad insertions.

Conclusions:

• The established heptad model for coiled coils needs to be expanded to incorporate hendecads.
• Combinations of heptads and hendecads create diverse sequence motifs, potentially facilitating specific protein-protein interactions during coiled-coil folding.
• Hendecad insertions offer a mechanism to reconcile breaks in extended coiled-coil sequences.