Electron microscopic visualization of collagen aggregates without chemical staining

Area of Science:

• Biophysics
• Materials Science
• Biochemistry

Background:

• Collagen is a crucial structural protein with a complex molecular arrangement.
• Understanding collagen's ultrastructure is key to deciphering its biological functions.
• Electron microscopy is a primary tool for visualizing biomolecular structures.

Purpose of the Study:

• To investigate the structural basis of the banding pattern in unstained collagen segment-long-spacing crystallites (SLS).
• To correlate the observed banding pattern with the molecular properties of collagen.
• To determine the role of adenosine triphosphate (ATP) in collagen aggregation and structure.

Main Methods:

• Preparation of uni-directional collagen SLS aggregates by dialysis against acetic acid with ATP.
• Examination of unstained SLS aggregates using transmission electron microscopy (TEM).
• Comparison of TEM banding patterns with the distribution of amino acid residues and molecular weight along the collagen molecule.

Main Results:

• At least 20 distinct cross-striations were observed in unstained SLS aggregates.
• The banding pattern strongly correlated with the distribution of basic amino acid residues.
• ATP binding to basic residues significantly improved the correlation between the local density profile and the observed banding pattern.

Conclusions:

• The electron microscopic banding pattern of unstained collagen SLS is primarily determined by the local density profile along the molecule.
• Adenosine triphosphate (ATP) enhances this banding pattern by binding to positively charged basic residues.
• This study validates the fundamental principle that electron density in TEM correlates with material amount in biological samples.