A Collagen Triple Helix without the Superhelical Twist.

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biophysics

Background:

• Collagens are crucial structural proteins in the extracellular matrix and immune system.
• The packing of collagen triple helices into larger assemblies is not well understood.
• The C1q collagen-like region serves as a model for studying collagen assembly.

Purpose of the Study:

• To investigate the structural basis of collagen triple helix packing.
• To design and characterize novel collagenous assemblies using a peptide self-assembly system.
• To explore the conformational diversity of collagen assemblies.

Main Methods:

• Peptide self-assembly was used to create collagenous structures.
• Cryo-electron microscopy (cryo-EM) determined the structure of an assembly to 3.5 Å resolution.
• Atomic modeling and site-directed mutagenesis were employed to analyze interactions.

Main Results:

• A novel triple helix conformation with no superhelical twist was identified.
• This nontwisting region facilitates unique hydroxyproline stacking and forms hydrophobic cavities.
• Designed assemblies with substituted amino acids confirmed the atomic model's predictions.

Conclusions:

• Collagen and collagen-like assemblies exhibit greater conformational diversity than previously thought.
• Unusual packing arrangements may occur at helix termini and sequence discontinuities.
• Findings have implications for understanding collagen-associated diseases.