Compressed microfibril models of the native collagen fibril

Area of Science:

• Biophysics
• Structural Biology
• Biochemistry

Background:

• A recent three-dimensional crystal model for collagen type I packing in native fibrils by Hulmes and Miller explains X-ray diffraction patterns and fibril density.
• Independent evidence from electron microscopy, in vitro assembly, crosslinking, and sequence analysis suggests a well-defined microfibrillar substructure absent in the Hulmes and Miller model.

Purpose of the Study:

• To reconcile the conflict between existing crystal packing models and evidence for microfibrillar substructure in collagen type I fibrils.
• To propose new models that incorporate both crystal lattice features and microfibrillar organization.

Main Methods:

• Development of two new models for collagen type I fibril structure.
• These models feature five-stranded microfibrils compressed onto a pseudohexagonal lattice.
• Comparison of proposed unit cells with the Hulmes and Miller model.

Main Results:

• The proposed models contain five-stranded microfibrils with collagen molecules arranged on a pseudohexagonal lattice.
• The unit cells of the new models are equivalent or related to the Hulmes and Miller cell.
• The models allow for both straight-tilted molecules/microfibrils and supercoiled molecules within straight microfibrils, with noncrystallographic data favoring supercoiling.

Conclusions:

• The proposed models successfully integrate the microfibrillar substructure with the overall fibril packing.
• Collagen type I fibrils may contain five-stranded microfibrils, potentially with supercoiled molecules.
• These findings offer a more comprehensive understanding of collagen fibril assembly and structure.