Electron microscopy shows periodic structure in collagen fibril cross sections

Area of Science:

• Biophysics
• Materials Science
• Structural Biology

Background:

• Collagen fibrils are essential structural proteins.
• Preserving their crystalline order during electron microscopy is challenging.
• Understanding collagen's 3D structure is vital for tissue engineering and disease research.

Purpose of the Study:

• To assess the impact of electron microscopy preparation techniques on collagen fibril crystalline order.
• To develop and validate a method for preserving this order.
• To correlate X-ray diffraction data with electron microscopy observations.

Main Methods:

• X-ray diffraction was used to analyze rat tail tendon collagen.
• Electron microscopy fixation, staining, and embedding procedures were evaluated.
• Optical diffraction of electron micrographs was performed.
• Comparison with native X-ray diffraction data.

Main Results:

• A procedure was established to preserve the 3.8-nm lateral spacing in collagen fibrils.
• This preserved spacing showed increased contrast in diffraction patterns.
• The 3.8-nm spacing correlated with observed density lines in ultrathin cross-sections.
• Optical diffraction indicated concentric crystalline domains within fibrils.

Conclusions:

• The described procedure effectively preserves collagen fibril crystalline order for electron microscopy.
• The findings support a model of collagen fibrils composed of concentric crystalline domains.
• This work advances the understanding of collagen's three-dimensional structure.