Early assembly pathways of type I collagen

Area of Science:

• Biophysics
• Materials Science
• Polymer Physics

Background:

• Type I collagen self-assembly is crucial for tissue structure.
• Understanding collagen aggregation pathways is key to biomaterial design.
• Existing models do not fully capture collagen's complex assembly dynamics.

Purpose of the Study:

• To develop a computational method for calculating the free energy of collagen aggregates.
• To investigate the preferred molecular alignments during collagen assembly.
• To identify key intermediate species in collagen fibrillogenesis.

Main Methods:

• Adapted the Matheson and Flory treatment for rigid rod polymer phase equilibria.
• Incorporated polymer-solvent interactions based on near-neighbor transfer energies.
• Assigned distinct interaction energies to helical and extrahelical collagen domains.

Main Results:

• The D-staggered (670 Å) molecular alignment is thermodynamically preferred over nematic alignment.
• One-dimensional (1D) staggered oligomers are predicted as early assembly intermediates.
• Four-dimensional (4D) dimers and 4D-8D trimers are generally not major intermediates, contradicting prior hypotheses.
• Inclusion of activation energies introduced uncertainty, identifying conditions where 4D dimers/trimers could be early species.

Conclusions:

• The developed method provides insights into collagen free energy and assembly.
• Thermodynamic favorability points to 1D staggered oligomers as initial assembly products.
• The role of 4D dimers and trimers as early intermediates is context-dependent, influenced by activation energies.