Quasi-hexagonal molecular packing in collagen fibrils

Area of Science:

• Biophysics
• Structural Biology
• Materials Science

Background:

• Collagen fibrils, essential for connective tissues, are traditionally modeled as rope-like microfibrils.
• Previous models proposed various microfibril strand numbers (2- to 8-stranded) based on X-ray diffraction data.
• These models suggested tetragonal packing within the fibril's crystalline lattice.

Purpose of the Study:

• To re-interpret medium-angle X-ray diffraction data of native collagen fibrils.
• To propose an alternative structural model for the crystalline regions of collagen fibrils.
• To challenge the microfibrillar hypothesis of collagen assembly.

Main Methods:

• Analysis of medium-angle X-ray diffraction patterns from native tendon fibers.
• Re-interpretation of Bragg reflections to infer molecular arrangement.
• Development of a new structural model for collagen fibril crystalline regions.

Main Results:

• The re-interpreted X-ray data supports a model of quasi-hexagonal molecular packing.
• This new model refutes the existence of discrete microfibrillar substructures within collagen fibrils.
• Collagen fibrils are proposed to be molecular crystals rather than aggregates of microfibrils.

Conclusions:

• The microfibrillar model of collagen assembly is likely incorrect.
• Collagen fibrils exhibit a crystalline structure based on quasi-hexagonal packing.
• This finding necessitates a revision of our understanding of collagen fibril organization and biogenesis.